| 1. |
- Malusek, Alexandr, 1968-
(författare)
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Calculation of scatter in cone beam CT : Steps towards a virtual tomograph
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Scattered photons—shortly scatter—are generated by interaction processes when photon beams interact with matter. In diagnostic radiology, they deteriorate image quality since they add an undesirable signal that lowers the contrast in projection radiography and causes cupping and streak artefacts in computed tomography (CT). Scatter is one of the most detrimental factors in cone beam CT owing to irradiation geometries using wide beams. It cannot be fully eliminated, nevertheless its amount can be lowered via scatter reduction techniques (air gaps, antiscatter grids, collimators) and its effect on medical images can be suppressed via scatter correction algorithms.Aim: Develop a tool—a virtual tomograph—that simulates projections and performs image reconstructions similarly to a real CT scanner. Use this tool to evaluate the effect of scatter on projections and reconstructed images in cone beam CT. Propose improvements in CT scanner design and image reconstruction algorithms.Methods: A software toolkit (CTmod) based on the application development framework ROOT was written to simulate primary and scatter projections using analytic and Monte Carlo methods, respectively. It was used to calculate the amount of scatter in cone beam CT for anthropomorphic voxel phantoms and water cylinders. Configurations with and without bowtie filters, antiscatter grids, and beam hardening corrections were investigated. Filtered back-projection was used to reconstruct images. Automatic threshold segmentation of volumetric CT data of anthropomorphic phantoms with known tissue compositions was tested to evaluate its usability in an iterative image reconstruction algorithm capable of performing scatter correction.Results: It was found that computer speed was the limiting factor for the deployment of this method in clinical CT scanners. It took several hours to calculate a single projection depending on the complexity of the geometry, number of simulated detector elements, and statistical precision. Data calculated using the CTmod code confirmed the already known facts that the amount of scatter is almost linearly proportional to the beam width, the scatter-to-primary ratio (SPR) can be larger than 1 for body-size objects, and bowtie filters can decrease the SPR in certain regions of projections. Ideal antiscatter grids significantly lowered the amount of scatter. The beneficial effect of classical antiscatter grids in cone beam CT with flat panel imagers was not confirmed by other researchers nevertheless new grid designs are still being tested. A simple formula estimating the effect of scatter on the quality of reconstructed images was suggested and tested.Conclusions: It was shown that computer simulations could calculate the amount of scatter in diagnostic radiology. The Monte Carlo method was too slow for a routine use in contemporary clinical practice nevertheless it could be used to optimize CT scanner design and, with some enhancements, it could become a part of an image reconstruction algorithm that performs scatter correction.
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| 2. |
- Alm Carlsson, Gudrun, et al.
(författare)
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Monte Carlo metoden : ett verktyg inom strålningsfysiken
- 1995
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Detta kompendium är tänkt att användas som ett propedeutiskt kursmaterial för kursdeltagare i kursen "Monte Carlo simulering av foton- och elektrontransport vid diagnostiska och radioterapeutiska strålkvaliteter". Först följer en kort repetition av den grundläggande statistik som utnyt1jas i beräkningarna. Därefter följer en beskrivning av slumptal. det fundament som metoden bygger på. Vidare beskrivs val ur olika frekvensfunktioner. Valet kan även göras ur så kallade falska fördelningar för att reducera variansen i den skattade storheten. Metoderna belyses i ett avsnitt om problemlösningsmetodik. först i allmänna termer för att sen gå in på ett specifikt problem (Buffons nålproblem) där en analys och strukturering av problemet görs varefter flödesschema och kodning exemplifieras. Så följer två moment där en beskrivning görs av färderna av fotoner respektive elektroner genom materia. För elektronfärderna gör man en indelning i klass 1- och klass II-färder. Vad detta innebär och hur deltapartiklar tas om hand beskrivs i ett kapitel. Till sist kommer en kort introduktion till de tre laborationerna med laborationshandledningar. Speciell vikt har lagts vid att initiera laboranten att fundera på fysiken i de simulerade experimenten. Detta kompendium har tillkommit som examinationsarbete vid en kurs i "Monte Carlo simulering av foton- och elektrontransport vid diagnostiska och radioterapeutiska strålkvaliteter", med andra ord den kurs du själv nu ämnar studera. Författarna önskar dig lycka till med kursen och hoppas att du kommer att få glädje av den. Speciellt hoppas vi att denna skrift ska underlätta för dig att tillgodogöra dig informationen vid föreläsningarna och under laborationerna.
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| 3. |
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| 4. |
- Andersson, Mats, et al.
(författare)
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Adaptiv filtering of 4D-heart CT for image denoising and patient safety
- 2010
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this medical image science project is to increase patient safety in terms of improved image quality and reduced exposure to ionizing radiation in CT. The means to achieve these goals is to develop and evaluate an efficient adaptive filtering (denoising/image enhancement) method that fully explores true 4D image acquisition modes. Four-dimensional (4D) medical image data are captured as a time sequence of image volumes. During 4D image acquisition, a 3D image of the patient is recorded at regular time intervals. The resulting data will consequently have three spatial dimensions and one temporal dimension. Increasing the dimensionality of the data impose a major increase the computational demands. The initial linear filtering which is the cornerstone in all adaptive image enhancement algorithms increase exponentially with the dimensionality. On the other hand the potential gain in Signal to Noise Ratio (SNR) also increase exponentially with the dimensionality. This means that the same gain in noise reduction that can be attained by performing the adaptive filtering in 3D as opposed to 2D can be expected to occur once more by moving from 3D to 4D. The initial tests on on both synthetic and clinical 4D images has resulted in a significant reduction of the noise level and an increased detail compared to 2D and 3D methods. When tuning the parameters for adaptive filtering is extremely important to attain maximal diagnostic value which not necessarily coincide with an an eye pleasing image for a layman. Although this application focus on CT the resulting adaptive filtering methods will be beneficial for a wide range of 3D/4D medical imaging modalities e.g. shorter acquisition time in MRI and improved elimination of noise in 3D or 4D ultrasound datasets.
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| 5. |
- Baranowski, Jacek, et al.
(författare)
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Echo-guided presentation of the aortic valve minimises contrast exposure in transcatheter valve recipients
- 2011
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Ingår i: Catheterization and cardiovascular interventions. - : Wiley. - 1522-1946 .- 1522-726X. ; 77:2, s. 272-275
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: We have developed a method using transthoracic echocardiography in establishing optimal visualization of the aortic root, to reduce the amount of contrast medium used in each patient. BACKGROUND: During transcatheter aortic valve implantation, it is necessary to obtain an optimal fluoroscopic projection for deployment of the valve showing the aortic ostium with the three cusps aligned in the beam direction. This may require repeat aortic root angiograms at this stage of the procedure with a high amount of contrast medium with a risk of detrimental influence on renal function. METHODS: We studied the conventional way and an echo guided way to optimize visualisation of the aortic root. Echocardiography was used initially allowing easier alignment of the image intensifier with the transducer's direction. RESULTS: Contrast volumes, radiation/fluoroscopy exposure times, and postoperative creatinine levels were significantly less in patients having the echo-guided orientation of the optimal fluoroscopic angles compared with patients treated with the conventional approach. CONCLUSION: We present a user-friendly echo-guided method to facilitate fluoroscopy adjustment during transcatheter aortic valve implantation. In our series, the amounts of contrast medium and radiation have been significantly reduced, with a concomitant reduction in detrimental effects on renal function in the early postoperative phase.
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| 6. |
- Borgen, Lars, et al.
(författare)
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Application of adaptive non-linear 2D and 3D postprocessing filters for reduced dose abdominal CT
- 2012
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Ingår i: Acta Radiologica. - : Informa Healthcare / Wiley-Blackwell / Royal Society of Medicine Press. - 0284-1851 .- 1600-0455. ; 53:3, s. 335-342
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Tidskriftsartikel (refereegranskat)abstract
- Background: Abdominal computed tomography (an is a frequently performed imaging procedure, resulting in considerable radiation doses to the patient population. Postprocessing filters are one of several dose reduction measures that might help to reduce radiation doses without loss of image quality. less thanbrgreater than less thanbrgreater thanPurpose: To assess and compare the effect of two- and three-dimensional (2D, 3D) non-linear adaptive filters on reduced dose abdominal CT images. less thanbrgreater than less thanbrgreater thanMaterial and Methods: Two baseline abdominal CT image series with a volume computer tomography dose index (CTDI (vol)) of 12 mGy and 6 mGy were acquired for 12 patients. Reduced dose images were postprocessed with 2D and 3D filters. Six radiologists performed blinded randomized, side-by-side image quality assessments. Objective noise was measured. Data were analyzed using visual grading regression and mixed linear models. less thanbrgreater than less thanbrgreater thanResults: All image quality criteria were rated as superior for 3D filtered images compared to reduced dose baseline and 2D filtered images (P andlt; 0.01). Standard dose images had better image quality than reduced dose 3D filtered images (P andlt; 0.01), but similar image noise. For patients with body mass index (BMI) andlt; 30 kg/m(2) however, 3D filtered images were rated significantly better than normal dose images for two image criteria (P andlt; 0.05), while no significant difference was found for the remaining three image criteria (P andgt; 0.05). There were no significant variations of objective noise between standard dose and 2D or 3D filtered images. less thanbrgreater than less thanbrgreater thanConclusion: The quality of 3D filtered reduced dose abdominal CT images is superior compared to reduced dose unfiltered and 2D filtered images. For patients with BMI andlt; 30 kg/m(2), 3D filtered images are comparable to standard dose images.
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| 7. |
- Dance, D, et al.
(författare)
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Breast dosimetry using high-resolution voxel phantoms
- 2005
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 359-363
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Tidskriftsartikel (refereegranskat)abstract
- A computer model of X-ray mammography has been developed, which uses quasi-realistic high-resolution voxel phantoms to simulate the breast. The phantoms have 400 μm voxels and simulate the three-dimensional distributions of adipose and fibroglandular tissues, Cooper's ligaments, ducts and skin and allow the estimation of dose to individual tissues. Calculations of the incident air kerma to mean glandular dose conversion factor, g, were made using a Mo/Mo spectrum at 28 kV for eight phantoms in the thickness range 40-80 mm and of varying glandularity. The values differed from standard tabulations used for breast dosimetry by up to 43%, because of the different spatial distribution of glandular tissue within the breast. To study this further, additional voxel phantoms were constructed, which gave variations of between 9 and 59% compared with standard values. For accurate breast dosimetry, it is therefore very important to take the distribution of glandular tissues into account. © The Author 2005. Published by Oxford University Press. All rights reserved.
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| 8. |
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| 9. |
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| 10. |
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| 11. |
- Dance, David, et al.
(författare)
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Optimisation of the design of antiscatter grids by computer modelling
- 1995
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Ingår i: Radiation Protection Dosimetry. - 0144-8420 .- 1742-3406. ; 57:1, s. 207-210
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Tidskriftsartikel (refereegranskat)abstract
- A Monte Carlo computer program has been developed to model diagnostic radiological examinations, and has been used to study and optimise the design of antiscatter grids. This is important because the use of an inappropriate or poorly designed grid can lead to increased patient dose. Optimal grid parameters may be different for large and small scattering volumes. The program treats the patient as a rectangular block of tissue and takes account of the grid and image receptor. Image quality is measured in terms of contrast and signal-to-noise ratio and patient risk in terms of mean absorbed dose. Test objects of appropriate size and composition are used in the calculation of these image quality parameters. A new performance comparison and optimisation procedure has been developed, and the program has been used to study grid design in screen-film and digital radiology for small, medium and large scattering volumes.
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| 12. |
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| 13. |
- Dance, David, et al.
(författare)
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The use of carbon fibre material in radiographic cassettes: estimation of the dose and contrast advantages
- 1997
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Ingår i: British Journal of Radiology. - 0007-1285 .- 1748-880X. ; 70, s. 383-390
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Tidskriftsartikel (refereegranskat)abstract
- A Monte Carlo simulation has been used to estimate the dose and contrast advantages of replacing radiographic cassette fronts fabricated from aluminium with cassette fronts fabricated from low atomic number material (carbon fibre). The simulation used a realistic imaging geometry and calculations were made both with and without an anti-scatter grid. Account was taken of the scatter generated in the cassette front and the effect of beam hardening on primary contrast. Dose and contrast were evaluated for a range of cassette front thicknesses and tube potentials (60-150 kV) as well as for four examinations representative of situations with varying amounts of scatter. The results with an anti-scatter grid show a clear dose and contrast advantage in all cases when an aluminium cassette front is replaced with a low attenuation cassette front. The contrast advantage is dependent upon the examination and is generally greater for imaging bony structures than for imaging soft tissue. If a 1.74 mm aluminium cassette front is compared with a 1.1 mm carbon fibre cassette front, then the dose advantages are 16%, 9%, 8% and 6% and the contrast advantages are 10%, 7%, 4% and 5% for the AP paediatric pelvis examination at 60 kV, the anteroposterior (AP) lumbar spine examination at 80 kV, the lateral lumbar spine examination at 100 kV and the posteroanterior (PA) chest examination at 150 kV, respectively. The results without an anti-scatter grid show an increased dose advantage when a low attenuation cassette front is used, but the contrast advantage is small and in some situations negative.
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| 14. |
- De Geer, Jakob, 1970-
(författare)
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On the use of computed tomography in cardiac imaging
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- BackgroundCardiac Computed Tomography Angiography (CCTA) is becoming increasingly useful in the work‐up of coronary artery disease (CAD). Several potential methods for increasing the diagnostic yield of cardiac CT are available.Purpose Study I: To investigate whether the use of a 2‐D, non‐linear adaptive noise reduction filter can improve CCTA image quality.Study II: To evaluate the variation in adenosine stress dynamic CT perfusion (CTP) blood flow as compared to stress 99mTc SPECT. Secondly, to compare the perfusion results from manual and automatic myocardial CTP segmentation.Study III: To evaluate the accuracy of non‐invasive, CCTA‐derived Fractional Flow Reserve (cFFR).Study IV: To evaluate the prognostic value of CCTA in terms of major adverse cardiac events (MACE).Materials and methodsStudy I: Single images from 36 consecutive CCTA exams performed with two different dose levels were used. Image quality in full dose, low‐dose and noise‐reduced low‐dose images was graded using visual grading analysis. Image noise was measured.Study II: CTP and SPECT were performed in 17 patients, and the variation in per AHA‐segment blood flow was evaluated and compared. CTP results from manual and automated image segmentation were compared.Study III: CCTA datasets from 21 patients were processed using cFFR software and the results compared to the corresponding invasively measured FFR (invFFR).Study IV: 1205 consecutive patients with chest pain of unknown origin underwent CCTA. Baseline data and data on subsequent MACE were retrieved from relevant registries. Survival, hazard ratios and the three‐year incidence of cardiac events and readmissions were calculated.Results Study I: There was significant improvement in perceived image quality for all criteria when the filter was applied, and a significant decrease in image noise.Study II: The correlation coefficients for CTP vs. SPECT were 0.38 and 0.41 (p<0.001, for manual and automated segmentation respectively. Mean per patient CTP blood flow in normal segments varied between 94‐183 ml/100 ml tissue/min for manual segmentation, and 104‐196 ml/100 ml tissue/min for automated segmentation. The Spearman rank correlation coefficient for manual vs. automated segmentation CTP was ρ = 0.88 (p<0.001) and the Intraclass Correlation Coefficient (ICC) was 0.93 (p<0.001).Study III: The Spearman rank correlation coefficient for cFFR vs. invFFR was ρ = 0.77 (p<0.001) and the ICC was 0.73 (p<0.001). Sensitivity, specificity, positive predictive value and negative predictive value for significant stenosis (FFR<0.80, per vessel) were 0.83, 0.76, 0.56 and 0.93 respectively.Study IV: The hazard ratio for non‐obstructive CAD vs. normal coronary arteries was 5.13 (95% C.I 1.03‐25.43, p<0.05), and 151.40 (95% C.I 37.03‐619.08, p<0.001) for obstructive CAD vs. normal coronary arteries. The three‐year incidence of MACE was 1.1% for patients with normal vessels on CCTA, 2.5% for patients with non‐obstructive CAD and 42.7% for patients with obstructive CAD (p<0.001).Conclusions:Study I: Image quality and noise levels of low dose images were significantly improved with the filter, even though the improvement was small compared to the image quality of the corresponding diastolic full‐dose images.Study II: Correlation between dynamic CTP and SPECT was positive but weak. There were large variations in CTP blood flow in normal segments on SPECT, rendering the definition of an absolute cut‐off value for normal vs. ischemic myocardium difficult. Manual and automatic segmentation were equally useful.Study III: The correlation between cFFR and invFFR was good, indicating that noninvasively estimated cFFR performs on a similar level as invasively measure FFR. Study IV: The long‐term risk for MACE was very low in patients without obstructive CAD on CCTA, though there seemed to be a substantial increase in the risk for MACE even in patients with non‐obstructive CAD as compared to normal coronary arteries. In addition, even patients with normal coronary arteries or non‐obstructive CAD continued to have a substantial number of readmissions for chest pain or angina pectoris.
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| 15. |
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| 16. |
- de Geer, Jakob, et al.
(författare)
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The efficacy of 2D, non-linear noise reduction filtering in cardiac imaging: a pilot study
- 2011
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Ingår i: Acta Radiologica. - : Informa Healthcare / Wiley-Blackwell / Royal Society of Medicine Press. - 0284-1851 .- 1600-0455. ; 52:7, s. 716-722
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Tidskriftsartikel (refereegranskat)abstract
- Background: Computed tomography (CT) is becoming increasingly popular as a non-invasive method for visualizing the coronary arteries but patient radiation doses are still an issue. Postprocessing filters such as 2D adaptive non-linear filters might help to reduce the dose without loss of image quality. less thanbrgreater than less thanbrgreater thanPurpose: To investigate whether the use of a 2D, non-linear adaptive noise reduction filter can improve image quality in cardiac computed tomography angiography (CCTA). less thanbrgreater than less thanbrgreater thanMaterial and Methods: CCTA examinations were performed in 36 clinical patients on a dual source CT using two patient dose levels: maximum dose during diastole and reduced dose (20% of maximum dose) during systole. One full-dose and one reduced-dose image were selected from each of the examinations. The reduced-dose image was duplicated and one copy postprocessed using a 2D non-linear adaptive noise reduction filter, resulting in three images per patient. Image quality was assessed using visual grading with three criteria from the European guidelines for assessment of image quality and two additional criteria regarding the left main artery and the overall image quality. Also, the HU value and its standard deviation were measured in the ascending and descending aorta. Data were analyzed using Visual Grading Regression and paired t-test. less thanbrgreater than less thanbrgreater thanResult: For all five criteria, there was a significant (P andlt; 0.01 or better) improvement in perceived image quality when comparing postprocessed low-dose images with low-dose images without noise reduction. Comparing full dose images with postprocessed low-dose images resulted in a considerably larger, significant (P andlt; 0.001) difference. Also, there was a significant reduction of the standard deviation of the HU values in the ascending and descending aorta when comparing postprocessed low-dose images with low-dose images without postprocessing. less thanbrgreater than less thanbrgreater thanConclusion: Even with an 80% dose reduction, there was a significant improvement in the perceived image quality when using a 2D noise-reduction filter, though not approaching the quality of full-dose images. This indicates that cardiac CT examinations could benefit from noise-reducing postprocessing with 2D non-linear adaptive filters.
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| 17. |
- Dohlmar, Frida, et al.
(författare)
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An audit of high dose-rate prostate brachytherapy treatment planning at six Swedish clinics
- 2021
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Ingår i: Journal of Contemporary Brachytherapy. - : TERMEDIA PUBLISHING HOUSE LTD. - 1689-832X .- 2081-2841. ; 13:1, s. 59-71
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: High dose-rate prostate brachytherapy has been implemented in Sweden in the late 1980s and early 1990s in six clinics using the same schedule: 20 Gy in two fractions combined with 50 Gy in 25 fractions with external beam radiation therapy. Thirty years have passed and during these years, various aspects of the treatment process have developed, such as ultrasound-guided imaging and treatment planning system. An audit was conducted, including a questionnaire and treatment planning, which aimed to gather knowledge about treatment planning methods in Swedish clinics. Material and methods: A questionnaire and a treatment planning case (non-anatomical images) were sent to six Swedish clinics, in which high-dose-rate prostate brachytherapy is performed. Treatment plans were compared using dosimetric indices and equivalent 2 Gy doses (EQD(2)). Treatment planning system report was used to compare dwell positions and dwell times. Results: For all the clinics, the planning aim for the target was 10.0 Gy, but the volume to receive the dose differed from 95% to 100%. Dose constraints for organs at risk varied with up to 2 Gy. The dose to 90% of target volume ranged from 10.0 Gy to 11.1 Gy, equivalent to 26.0 Gy EQD(2) and 31.3 Gy EQD(2), respectively. Dose non-homogeneity ratio differed from 0.18 to 0.32 for clinical target volume (CTV) in treatment plans and conformity index ranged from 0.52 to 0.59 for CTV. Conclusions: Dose constraints for the organs at risk are showing a larger variation than that reflected in compared treatments plans. In all treatment plans in our audit, at least 10 Gy was administered giving a total treatment of 102 Gy EQD(2), which is in the upper part of the prescription doses published in the GEC/ESTRO recommendations.
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| 18. |
- Dohlmar, Frida, et al.
(författare)
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Validation of automated post-adjustments of HDR prostate brachytherapy treatment plans by quantitative measures and oncologist observer study
- 2023
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Ingår i: Brachytherapy. - : Elsevier BV. - 1538-4721 .- 1873-1449. ; 22:3, s. 407-415
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: The aim was to evaluate a postprocessing optimization algorithm's ability to improve the spatial properties of a clinical treatment plan while preserving the target coverage and the dose to the organs at risk. The goal was to obtain a more homogenous treatment plan, minimizing the need for manual adjustments after inverse treatment planning. MATERIALS AND METHODS: The study included 25 previously treated prostate cancer pa-tients. The treatment plans were evaluated on dose-volume histogram parameters established clin-ical and quantitative measures of the high dose volumes. The volumes of the four largest hot spots were compared and complemented with a human observer study with visual grading by eight oncologists. Statistical analysis was done using ordinal logistic regression. Weighted kappa and Fleiss' kappa were used to evaluate intra-and interobserver reliability. RESULTS: The quantitative analysis showed that there was no change in planning target volume (PTV) coverage and dose to the rectum. There were significant improvements for the adjusted treatment plan in: V150% and V200% for PTV, dose to urethra, conformal index, and dose nonhomogeneity ratio. The three largest hot spots for the adjusted treatment plan were significantly smaller compared to the clinical treatment plan. The observers preferred the adjusted treatment plan in 132 cases and the clinical in 83 cases. The observers preferred the adjusted treatment plan on homogeneity and organs at risk but preferred the clinical plan on PTV coverage. CONCLUSIONS: Quantitative analysis showed that the postadjustment optimization tool could improve the spatial properties of the treatment plans while maintaining the target coverage.
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| 19. |
- Elgström, Henrik, et al.
(författare)
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Signal-To-Noise Ratio Rate Measurement in Fluoroscopy For Quality Control and Teaching Good Radiological Imaging Technique
- 2021
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press. - 0144-8420 .- 1742-3406. ; 195:3-4, s. 407-415
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Tidskriftsartikel (refereegranskat)abstract
- Visibility of low-contrast details in fluoroscopy and interventional radiology is important. Assessing detail visibility with human observers typically suffers from large observer variances. Objective, quantitative measurement of low-contrast detail visibility using a model observer, such as the square of the signal-to-noise ratio rate (SNR2rate), was implemented in MATLAB™ and evaluated. The expected linear response of SNR2rate based on predictions by the so-called Rose model and frame statistics was verified. The uncertainty in the measurement of SNR2rate for a fixed imaging geometry was 6% based on 16 repeated measurements. The results show that, as expected, reduced object thickness and x-ray field size substantially improved SNR2rate/PKA,rate with PKA,rate being the air kerma area product rate. The measurement precision in SNR2rate/PKA,rate (8–9%) is sufficient to detect small but important improvements, may guide the selection of better imaging settings and provides a tool for teaching good radiological imaging techniques to clinical staff.
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| 20. |
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| 21. |
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| 22. |
- Gårdestig, Magnus, 1973-, et al.
(författare)
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Estimations of effective dose in X-ray examinations derived from information stored in PACS
- 2005
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Ingår i: Radiological Protection in Transition. - Stockholm : Statens Strålskyddsinstitut. ; , s. 175-178
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Information about each X-ray examination, in a modern digitized X-ray department is generated and stored in a PACS. Appropriate conversion factors, e.g. E/DAP, can be applied to separate projections and summed to the total effective dose for each examination. The objectives of the work were (i) to investigate the accuracy and precision in the calculated effective dose (ii) to identify data for registration of (1) patient dose, (2) exposure data, and (3) patient information (iii) to make it possible to derive dose statistics on patient level for documentation of diagnostic standard doses, optimizations, constancy checks, and future epidemiological studies. The effective doses were calculated using Monte Carlo based computer programs or by using tabulations. Conversion factors were calculated for different levels of information and the individual effective dose was compared to the most precise estimation. The results suggest that the accuracy in the estimations of effective dose increases by added information about the patient (gender, size) and how the examination was performed.
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| 23. |
- Hammersberg, P., et al.
(författare)
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A theoretical model for determination of the optimal irradiation conditions for computerised tomography
- 1995
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Ingår i: Insight. - 1354-2575 .- 1754-4904. ; 37:12, s. 978-985
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Tidskriftsartikel (refereegranskat)abstract
- Image quality in Computerised Tomography (CT) depends strongly on the quality of the CT-projection data. These depend on sample composition and geometry, contrasting details within the sample and the equipment used, i.e. X-ray spectra, filtration, detector response and geometry. This paper focuses on the problem of selecting the optimal physical parameters to maximise the signal-to-noise in CT projection data (SNRCT) between a contrasting detail and the surrounding sample for CT-scanners equipped with poly-energetic X-ray sources (conventional X-ray tubes) and energy-integrating detector systems (image intensifier and optical video chain). The work includes the derivation and verification ofa theoretical model for SNRCT which can be used for predicting the optimal physical parameters for specific imaging tasks. It is shown that simplified calculations valid for mono-energetic X-ray sources and/or photon counting detectors do not correctly predict the optimal settings. This study also includes measurements of the actual X-ray source and photon transport Monte Carlo simulations of the response of the detector system.
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| 24. |
- Hansson, Edvin, 1987-
(författare)
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Internal Dosimetry in Nuclear Fuel Fabrication : Occupational Exposure to Uranium Aerosols
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The production of nuclear fuel can be associated with occupational exposure to ionizing radiation from radioactive decay of uranium. Such exposure must be sufficiently low and radiation doses adequately determined. Radiation doses from internal exposure, i.e., following intake (usually inhalation), cannot be estimated using dosimeters, but must be calculated based on indirect measurements in combination with biokinetic models.Such biokinetic models have been developed and refined for decades. Good knowledge of the material characteristics is crucial. However, the physicochemical properties of chemical compounds can vary between different production facilities. Aerosol size distributions and dissolution characteristics in lung fluid are of particular importance. The latter is important since dissolved material is absorbed to blood, whereupon a large fraction reaches the urine after filtering by the kidneys. This enables urine sampling as a method to monitor occupational exposure.The aim of this thesis was to investigate the physicochemical properties of uranium aerosols and their implication on internal dose assessments at a nuclear fuel fabrication plant in Sweden. Uranium aerosols were sampled and size fractionated using personal cascade impactors carried by workers at the factory’s different main workshops. Aerosols were studied using scanning electron microscopy in Paper I. In Paper II the activity size distributions were determined and in Paper III dissolution rates in simulated lung fluid were investigated. Paper IV is an internal dose assessment based on records of urine sample analyses from about 10 years of routine occupational exposure monitoring of uranium pelletizing workers at the site.For a median worker, the urinary daily excretion rate of uranium increased due to chronic exposure for about 1000 days, after which the excretion rate stabilized. This suggests that inhaled material dissolves in the respiratory tract rapidly enough to prevent a net buildup in the lung after several years of exposure. This could be modelled using the default recommendations for uranium oxide materials provided by the International Commission on Radiological Protection. However, the best model fit to measurement data was obtained using a different set of parameters, that showed some discrepancies with results from Papers II-III. For individual cases, excretion rates could vary between sampling occasions to a greater extent than predicted using the default recommendations, which could indicate a more rapid body clearance than expected. Whether this is an effect of experimental methods or simplifications in the biokinetic models should be further investigated in future work.
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| 25. |
- Helmrot, Ebba, et al.
(författare)
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Estimation of the dose to the unborn child at diagnostic X-ray examinations based on data registrerad in RIS/PACS
- 2007
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Ingår i: European Radiology. - : Springer Science and Business Media LLC. - 0938-7994 .- 1432-1084. ; 17:1, s. 205-209
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work was to determine mean absorbed doses to the unborn child in common conventional X-ray and computed tomography (CT) examinations and to find an approach for estimating foetal dose based on data registered in the Radiological Information System/Picture Archive and Communication System (RIS/PACS). The kerma-area product (KAP) and CT dose index (CTDIvol) in common examinations were registered using a human-shaped female dosimetry phantom. Foetal doses, Df, were measured using thermoluminescent dosimeters placed inside the phantom and compared with calculated values. Measured foetal doses were given in relation to the KAP and the CTDIvol values, respectively. Conversion factor Df/KAP varies between 0.01 and 3.8 mGy/Gycm2, depending on primary beam position, foetus age and beam quality (tube voltage and filtration). Conversion factors Df/CTDIvol are in the range 0.02 – 1.2 mGy/mGy, in which the foetus is outside or within the primary beam. We conclude that dose conversion factors based on KAP or CTDIvol values automatically generated by the RIS/PACS system can be used for rapid estimations of foetal dose for common examination techniques.
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| 26. |
- Helmrot, Ebba, et al.
(författare)
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Influence of scattered radiation and tube potential on radiographic contrast: comparison of two different dental X-ray films
- 1991
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Ingår i: Dento-Maxillo-Facial Radiology. - 0250-832X .- 1476-542X. ; 20:3, s. 135-146
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Tidskriftsartikel (refereegranskat)abstract
- The fundamental concept in image quality of contrast has been analysed in terms of its elements; film, radiation and object contrast, and the theoretical formula to describe their interrelationship have been evaluated. Experiments were designed to investigate the dependence of radiographic contrast on the kV, the type of generator and dental film used (D and E speed). An ivory wedge was used as the object, both alone and within a polymethyl methacrylate phantom as scattering medium. Precise definition and control of the X-ray generators were achieved by means of measurements of the primary X-ray spectra using a Compton spectrometer. D speed was found to have higher film contrast than E speed when compared at the same optical density, due to its lower base and fog and lower level of saturation in these experiments. On the other hand, E speed was found to have wider latitude. The experimental object was reproduced with the highest radiographic contrast using D-speed film and, with a given type of generator, this increased when the kV was decreased. While no difference in scatter/primary ratios was observed using the two different films, a weak dependence on kV in the range from 36 to 77 kV was found and confirmed by Monte Carlo calculations. The results indicate that the D and E speed films used had equal energy absorption properties; the difference in radiographic performance is due to their different film characteristics. The importance of controlling the physical parameters (photon energy spectrum, base and fog and optical density level) when comparing image qualities is clearly demonstrated.
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| 27. |
- Helmrot, Ebba, et al.
(författare)
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Scientific instrument for a controlled choice of optimal photon energy in intra-oral radiography
- 1998
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Ingår i: Radiation Protection Dosimetry. - 0144-8420 .- 1742-3406. ; 80:1, s. 321-325
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Tidskriftsartikel (refereegranskat)abstract
- Basic performance parameters are defined and analysed in order to optimise physical image quality in relation to the energy imparted to the patient in dental radiology. Air cavities were embedded in well-defined multimaterial, hard tissue phantoms to represent various objects in dento-maxillo-facial examinations. Basic performance parameters were: object contrast (C), energy imparted (_) to the patient, signal-to-noise ration (SNR), C2/_ (film) and (SNR)2/_ (digital imaging system) as functions of HVL (half-value layer), used to describe the photon energy spectrum. For the film receptor, the performance index C2/_ is maximum (optimal) at HVL values of 1.5-1.7 mm Al in the simulated Incisive, Premolar and Molar examinations. Other imaging tasks (examinations), not simulated here, may require other optimal HVL. For the digital imaging system (Digora) the performance index (SNR)2/_, theoretically calculated, indicates that a lower value of HVL is optimal than with film as receptor. However, due to the limited number of bits (8 bits) in the analogue to digital converter (ADC) contrast resolution is degraded and calls for use of higher photon energies (HVL). Customised optimisations with proper concern for patient category, type of examination, diagnostic task is the ultimate goal of this work. The conclusions stated above give some general advice on the appropriate choice of photon energy spectrum (HVL). In particular situations, it may be necessary to use more dose demanding kV settings (lower HVL) in order to get sufficient image quality for the diagnostic task.
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| 28. |
- Helmrot, Ebba, et al.
(författare)
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Use of an ivory wedge as a test phantom in analysing the influence of scattered radiation and tube potential on radiolographic contrast in intraoral dental radiography
- 1993
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Ingår i: Radiation Protection Dosimetry. - 0144-8420 .- 1742-3406. ; 49:1, s. 125-127
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Tidskriftsartikel (refereegranskat)abstract
- Contrast, noise and spatial resolution are fundamental physical concepts used to describe image quality. Contrast is one of the most important parameters in conventional film radiography. To facilitate the analysis of the radiographic contrast over a wide range of optical densities, an ivory wedge representative of objects with marked tissue discontinuities has been constructed. It can be used either separately or included within a PMMA phantom representing the middle face to simulate realistic scatter conditions. It is thus possible to investigate how radiographic contrast may be influenced by kV setting, beam filtration, type of generator (constant potential or single pulse) and type of film. The phantom has been used in optimising image quality relative to radiation risk, with the radiographic contrast being determined both theoretically and experimentally in terms of type of film (D and E speed), radiation and object contrast. The importance of controlling physical parameters when investigating image quality and how to achieve this using a well defined phantom is clearly demonstrated.
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| 29. |
- Hillman, Jan, 1952-, et al.
(författare)
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Bedside monitoring of CBF with xenon-CT and a mobile scanner : A novel method in neurointensive care
- 2005
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Ingår i: British Journal of Neurosurgery. - : Informa UK Limited. - 0268-8697 .- 1360-046X. ; 19:5, s. 395-401
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Tidskriftsartikel (refereegranskat)abstract
- Combining previously independently established techniques our objective was to develop and evaluate a method for bedside qualitative assessment of cerebral blood flow in neurointensive care (NICU) patients. The CT-protocol was optimized using phantoms and comparing a mobile CT-scanner (Tomoscan-M, Philips) with two stationary CT scanners. Thirty-two per cent xenon was delivered with standard equipment (Enhancer 3000). Mean cortical flow in volunteers was 48 ml/min/100 g, with the mean vascular territorial flow varying between 45 and 66 ml/min/100 g. The potential clinical usefulness was illustrated in three patients with vasospasm following subarachnoid haemorrhage. Our conclusion is that quantitative bedside measurements of CBF can be repeatedly performed in an easy and safe way in a standard NICU-setting, using xenon-inhalation and a mobile CT-scanner. The method is useful for the decision-making, and is a good example of how the quality of multi-modality monitoring in the NICU can be developed and further diversified. © The Neurosurgical Foundation.
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| 30. |
- Hunt, R, et al.
(författare)
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Calculation of the properties of digital mammograms using a computer simulation
- 2005
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 395-398
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Tidskriftsartikel (refereegranskat)abstract
- A Mote Carlo computer model of mammography has been developed to study and optimise the performance of digital mammographic systems. The program uses high-resolution voxel phantoms to model the breast, which simulate the adipose and fibroglandular tissues, Cooper's ligaments, ducts and skin in three dimensions. The model calculates the dose to each tissue, and also the quantities such as energy imparted to image pixels, noise per image pixel and scatter-to-primary (S/P) ratios. It allows studies of the dependence of image properties on breast structure and on position within the image. The program has been calibrated by calculating and measuring the pixel values and noise for a digital mammographic system. The thicknesses of two components of this system were unknown, and were adjusted to obtain a good agreement between measurement and calculation. The utility of the program is demonstrated with the calculations of the variation of the S/P ratio with and without a grid, and of the image contrast across the image of a 50-mm-thick breast phantom. © The Author 2005. Published by Oxford University Press. All rights reserved.
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| 31. |
- Hunt, R, et al.
(författare)
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Monte Carlo simulation of a mammographic test phantom
- 2005
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 114:1-3, s. 432-435
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Tidskriftsartikel (refereegranskat)abstract
- A test phantom, including a wide range of mammographic tissue equivalent materials and test details, was imaged on a digital mammographic system. In order to quantify the effect of scatter on the contrast obtained for the test details, calculations of the scatter-to-primary ratio (S/P) have been made using a Monte Carlo simulation of the digital mammographic imaging chain, grid and test phantom. The results show that the S/P values corresponding to the imaging conditions used were in the range 0.084-0.126. Calculated and measured pixel values in different regions of the image were compared as a validation of the model and showed excellent agreement. The results indicate the potential of Monte Carlo methods in the image quality-patient dose process optimisation, especially in the assessment of imaging conditions not available on standard mammographic units. © The Author 2005. Published by Oxford University Press. All rights reserved.
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| 32. |
- Jeuthe, Julius, et al.
(författare)
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Semi-Automated 3D Segmentation of Pelvic Region Bones in CT Volumes for the Annotation of Machine Learning Datasets
- 2021
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press. - 0144-8420 .- 1742-3406. ; 195:3-4, s. 172-176
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Tidskriftsartikel (refereegranskat)abstract
- Automatic segmentation of bones in computed tomography (CT) images is used for instance in beam hardening correction algorithms where it improves the accuracy of resulting CT numbers. Of special interest are pelvic bones, which—because of their strong attenuation—affect the accuracy of brachytherapy in this region. This work evaluated the performance of the JJ2016 algorithm with the performance of MK2014v2 and JS2018 algorithms; all these algorithms were developed by authors. Visual comparison, and, in the latter case, also Dice similarity coefficients derived from the ground truth were used. It was found that the 3D-based JJ2016 performed better than the 2D-based MK2014v2, mainly because of the more accurate hole filling that benefitted from information in adjacent slices. The neural network-based JS2018 outperformed both traditional algorithms. It was, however, limited to the resolution of 1283 owing to the limited amount of memory in the graphical processing unit (GPU).
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| 33. |
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| 34. |
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| 35. |
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| 36. |
- Kalra, Mannudeep, et al.
(författare)
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Whole spine CT for evaluation of scoliosis in children : feasibility of sub-milliSievert scanning protocol
- 2013
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Ingår i: Acta Radiologica. - : Sage Publications. - 0284-1851 .- 1600-0455. ; 54:2, s. 226-230
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Tidskriftsartikel (refereegranskat)abstract
- Background Optimization of CT radiation dose is important for children due to their higher risk of radiation-induced adverse effects. Anatomical structures with high inherent contrast, such as bones can be imaged at very low radiation doses by optimizing scan parameters. Purpose To assess feasibility of sub-milliSievert whole spine CT scanning protocol for evaluation of scoliosis in children. Material and Methods With approval of the ethical board, we performed whole spine CT for evaluation of scoliosis in 22 children (age range, 3–18 years; mean age, 13 years; 13 girls, 9 boys) on a 128-slice dual source multidetector-row CT scanner. Lowest possible quality reference mAs value (image quality factor for xy-z automatic exposure control or xyz-AEC, CARE Dose 4D) was selected on a per patient basis. Remaining parameters were held constant at 3.0:1 pitch, 128 × 0.6 mm detector collimation, 115.2 mm table feed per gantry rotation, 100 kVp, and 1 and 3 mm reconstructed sections. Average mAs, projected estimated dose savings with AEC, computed tomography dose index volume (CTDI vol), and dose length product (DLP) were recorded. Artifacts were graded on a four-point scale (1, no artifacts; 4, severe artifacts). Ability to identify vertebral and pedicular contours, and measure pedicular width and degree of vertebral rotation was graded on a three-point scale (1, unacceptable; 3, excellent). Results All CT examinations were deemed as reliable for identifying vertebral and pedicular contours as well as for measuring pedicular width (5.9 ± 1.6 mm) and degree of vertebral rotation (28.7 ± 23.4°). Mean objective image noise and signal to noise ratio (SNR) were 57.5 ± 21.5 and 4.7 ± 2.3, respectively. With a mean quality reference mAs of 13, the scanner employed an average actual effective mAs of 10 ± 3.8 (range, 6–18 mAs) with an estimated radiation dose saving of 43.5 ± 16.3% with xyz-AEC compared with fixed mAs. The mean CTDI, DLP, and estimated effective doses were 0.4 ± 0.1 mGy (0.2–0.7 mGy), 21 ± 10 mGy.cm (8–41 mGy.cm), and 0.3 ± 0.1 mSv (0.12–0.64 mSv), respectively. Conclusion Radiation dose for whole spine CT for evaluation of scoliosis in children can be minimized to less than one-third of a milliSievert while maintaining diagnostic image quality.
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| 37. |
- Kardell, Martin, et al.
(författare)
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AUTOMATIC SEGMENTATION OF PELVIS FOR BRACHYTHERAPYOF PROSTATE
- 2016
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 169:1-4, s. 398-404
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Tidskriftsartikel (refereegranskat)abstract
- Advanced model-based iterative reconstruction algorithms in quantitative computed tomography (CT) perform automatic segmentation of tissues to estimate material properties of the imaged object. Compared with conventional methods, these algorithms may improve quality of reconstructed images and accuracy of radiation treatment planning. Automatic segmentation of tissues is, however, a difficult task. The aim of this work was to develop and evaluate an algorithm that automatically segments tissues in CT images of the male pelvis. The newly developed algorithm (MK2014) combines histogram matching, thresholding, region growing, deformable model and atlas-based registration techniques for the segmentation of bones, adipose tissue, prostate and muscles in CT images. Visual inspection of segmented images showed that the algorithm performed well for the five analysed images. The tissues were identified and outlined with accuracy sufficient for the dual-energy iterative reconstruction algorithm whose aim is to improve the accuracy of radiation treatment planning in brachytherapy of the prostate.
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| 38. |
- Kataria, Bharti, 1955-, et al.
(författare)
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Assessment of image quality in abdominal computed tomography : Effect of model-based iterative reconstruction, multi-planar reconstruction and slice thickness on potential dose reduction
- 2020
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Ingår i: European Journal of Radiology. - : Elsevier Ireland Ltd. - 0720-048X .- 1872-7727. ; 122
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To determine the effect of tube load, model-based iterative reconstruction (MBIR) strength and slice thickness in abdominal CT using visual comparison of multi-planar reconstruction images. Method: Five image criteria were assessed independently by four radiologists on two data sets at 42- and 98-mAs tube loads for 25 patients examined on a 192-slice dual-source CT scanner. Effect of tube load, MBIR strength, slice thickness and potential dose reduction was estimated with Visual Grading Regression (VGR). Objective image quality was determined by measuring noise (SD), contrast-to-noise (CNR) ratio and noise-power spectra (NPS). Results: Comparing 42- and 98-mAs tube loads, improved image quality was observed as a strong effect of log tube load regardless of MBIR strength (p < 0.001). Comparing strength 5 to 3, better image quality was obtained for two criteria (p < 0.01), but inferior for liver parenchyma and overall image quality. Image quality was significantly better for slice thicknesses of 2mm and 3mm compared to 1mm, with potential dose reductions between 24%-41%. As expected, with decrease in slice thickness and algorithm strength, the noise power and SD (HU-values) increased, while the CNR decreased. Conclusion: Increasing slice thickness from 1 mm to 2 mm or 3 mm allows for a possible dose reduction. MBIR strength 5 shows improved image quality for three out of five criteria for 1 mm slice thickness. Increasing MBIR strength from 3 to 5 has diverse effects on image quality. Our findings do not support a general recommendation to replace strength 3 by strength 5 in clinical abdominal CT protocols. However, strength 5 may be used in task-based protocols.
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| 39. |
- Kataria, Bharti, 1955-, et al.
(författare)
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Assessment of image quality in abdominal CT : potential dose reduction with model-based iterative reconstruction
- 2018
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Ingår i: European Radiology. - Heidelberg : SPRINGER. - 0938-7994 .- 1432-1084. ; 28:6, s. 2464-2473
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Tidskriftsartikel (refereegranskat)abstract
- To estimate potential dose reduction in abdominal CT by visually comparing images reconstructed with filtered back projection (FBP) and strengths of 3 and 5 of a specific MBIR. A dual-source scanner was used to obtain three data sets each for 50 recruited patients with 30, 70 and 100% tube loads (mean CTDIvol 1.9, 3.4 and 6.2 mGy). Six image criteria were assessed independently by five radiologists. Potential dose reduction was estimated with Visual Grading Regression (VGR). Comparing 30 and 70% tube load, improved image quality was observed as a significant strong effect of log tube load and reconstruction method with potential dose reduction relative to FBP of 22-47% for MBIR strength 3 (p < 0.001). For MBIR strength 5 no dose reduction was possible for image criteria 1 (liver parenchyma), but dose reduction between 34 and 74% was achieved for other criteria. Interobserver reliability showed agreement of 71-76% (kappa (w) 0.201-0.286) and intra-observer reliability of 82-96% (kappa (w) 0.525-0.783). MBIR showed improved image quality compared to FBP with positive correlation between MBIR strength and increasing potential dose reduction for all but one image criterion. aEuro cent MBIR's main advantage is its de-noising properties, which facilitates dose reduction. aEuro cent MBIR allows for potential dose reduction in relation to FBP. aEuro cent Visual Grading Regression (VGR) produces direct numerical estimates of potential dose reduction. aEuro cent MBIR strengths 3 and 5 dose reductions were 22-34 and 34-74%. aEuro cent MBIR strength 5 demonstrates inferior performance for liver parenchyma.
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| 40. |
- Kataria, Bharti, et al.
(författare)
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Image quality and pathology assessment in CT Urography : when is the low-dose series sufficient?
- 2019
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Ingår i: BMC Medical Imaging. - : BMC. - 1471-2342. ; 19:1
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Tidskriftsartikel (refereegranskat)abstract
- Background Our aim was to compare CT images from native, nephrographic and excretory phases using image quality criteria as well as the detection of positive pathological findings in CT Urography, to explore if the radiation burden to the younger group of patients or patients with negative outcomes can be reduced. Methods This is a retrospective study of 40 patients who underwent a CT Urography examination on a 192-slice dual source scanner. Image quality was assessed for four specific renal image criteria from the European guidelines, together with pathological assessment in three categories: renal, other abdominal, and incidental findings without clinical significance. Each phase was assessed individually by three radiologists with varying experience using a graded scale. Certainty scores were derived based on the graded assessments. Statistical analysis was performed using visual grading regression (VGR). The limit for significance was set at p = 0.05. Results For visual reproduction of the renal parenchyma and renal arteries, the image quality was judged better for the nephrogram phase (p < 0.001), whereas renal pelvis/calyces and proximal ureters were better reproduced in the excretory phase compared to the native phase (p < 0.001). Similarly, significantly higher certainty scores were obtained in the nephrogram phase for renal parenchyma and renal arteries, but in the excretory phase for renal pelvis/calyxes and proximal ureters. Assessment of pathology in the three categories showed no statistically significant differences between the three phases. Certainty scores for assessment of pathology, however, showed a significantly higher certainty for renal pathology when comparing the native phase to nephrogram and excretory phase and a significantly higher score for nephrographic phase but only for incidental findings. Conclusion Visualisation of renal anatomy was as expected with each post-contrast phase showing favourable scores compared to the native phase. No statistically significant differences in the assessment of pathology were found between the three phases. The low-dose CT (LDCT) seems to be sufficient in differentiating between normal and pathological examinations. To reduce the radiation burden in certain patient groups, the LDCT could be considered a suitable alternative as a first line imaging method. However, radiologists should be aware of its limitations.
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| 41. |
- Kataria, Bharti, 1955-, et al.
(författare)
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Image Quality and Potential Dose Reduction Using Advanced Modeled Iterative Reconstruction (Admire) in Abdominal Ct : A Review
- 2021
-
Ingår i: Radiation Protection Dosimetry. - : Oxford University Press. - 0144-8420 .- 1742-3406. ; 195:3-4, s. 177-187
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Forskningsöversikt (refereegranskat)abstract
- Traditional filtered back projection (FBP) reconstruction methods have served the computed tomography (CT) community wellfor over 40 years. With the increased use of CT during the last decades, efforts to minimise patient exposure, while maintainingsufficient or improved image quality, have led to the development of model-based iterative reconstruction (MBIR) algorithms fromseveral vendors. The usefulness of the advanced modeled iterative reconstruction (ADMIRE) (Siemens Healthineers) MBIR inabdominal CT is reviewed and its noise suppression and/or dose reduction possibilities explored. Quantitative and qualitativemethods with phantom and human subjects were used. Assessment of the quality of phantom images will not always correlatepositively with those of patient images, particularly at the higher strength of the ADMIRE algorithm. With few exceptions,ADMIRE Strength 3 typically allows for substantial noise reduction compared to FBP and hence to significant (≈30%) patientdose reductions. The size of the dose reductions depends on the diagnostic task.
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| 42. |
- Kataria, Bharti, 1955-, et al.
(författare)
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Image quality in CT thorax: effect of altering reconstruction algorithm and tube load : Image quality in CT thorax
- 2024
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press. - 0144-8420 .- 1742-3406. ; 200:5, s. 504-514
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Tidskriftsartikel (refereegranskat)abstract
- Non-linear properties of iterative reconstruction (IR) algorithms can alter image texture. We evaluated the effect of a model-basedIR algorithm (advanced modelled iterative reconstruction; ADMIRE) and dose on computed tomography thorax image quality.Dual-source scanner data were acquired at 20, 45 and 65 reference mAs in 20 patients. Images reconstructed with filteredback projection (FBP) and ADMIRE Strengths 3–5 were assessed independently by six radiologists and analysed using an ordinallogistic regression model. For all image criteria studied, the effects of tube load 20 mAs and all ADMIRE strengths were significant(p < 0.001) when compared to reference categories 65 mAs and FBP. Increase in tube load from 45 to 65 mAs showed imagequality improvement in three of six criteria. Replacing FBP with ADMIRE significantly improves perceived image quality for allcriteria studied, potentially permitting a dose reduction of almost 70% without loss in image quality
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| 43. |
- Kataria, Bharti, et al.
(författare)
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IMPLICATIONS OF PATIENT CENTRING ON ORGAN DOSE IN COMPUTED TOMOGRAPHY
- 2016
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press. - 0144-8420 .- 1742-3406. ; 169:1-4, s. 130-135
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Tidskriftsartikel (refereegranskat)abstract
- Automatic exposure control (AEC) in computed tomography (CT) facilitates optimisation of dose absorbed by the patient. The use of AEC requires appropriate ‘patient centring’ within the gantry, since positioning the patient off-centre may affect both image quality and absorbed dose. The aim of this experimental study was to measure the variation in organ and abdominal surface dose during CTexaminations of the head, neck/thorax and abdomen. The dose was compared at the isocenter with two off-centre positions—ventral and dorsal to the isocenter. Measurements were made with an anthropomorphic adult phantom and thermoluminescent dosemeters. Organs and surfaces for ventral regions received lesser dose (5.6–39.0 %) than the isocenter when the phantom was positioned 13 cm off-centre. Similarly, organ and surface doses for dorsal regions were reduced by 5.0–21.0 % at 25 cm off-centre. Therefore, correct vertical positioning of the patient at the gantry isocenter is important to maintain optimal imaging conditions.
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| 44. |
- Kataria, Bharti, 1955-, et al.
(författare)
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Learning effects in visual grading assessment of model-based reconstruction algorithms in abdominal Computed Tomography
- 2023
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Ingår i: EUROPEAN JOURNAL OF RADIOLOGY OPEN. - : Elsevier BV. - 2352-0477. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Images reconstructed with higher strengths of iterative reconstruction algorithms may impair radi-ologists' subjective perception and diagnostic performance due to changes in the amplitude of different spatial frequencies of noise. The aim of the present study was to ascertain if radiologists can learn to adapt to the unusual appearance of images produced by higher strengths of Advanced modeled iterative reconstruction al-gorithm (ADMIRE). Methods: Two previously published studies evaluated the performance of ADMIRE in non-contrast and contrast -enhanced abdominal CT. Images from 25 (first material) and 50 (second material) patients, were reconstructed with ADMIRE strengths 3, 5 (AD3, AD5) and filtered back projection (FBP). Radiologists assessed the images using image criteria from the European guidelines for quality criteria in CT. To ascertain if there was a learning effect, new analyses of data from the two studies was performed by introducing a time variable in the mixed -effects ordinal logistic regression model. Results: In both materials, a significant negative attitude to ADMIRE 5 at the beginning of the viewing was strengthened during the progress of the reviews for both liver parenchyma (first material:-0.70, p < 0.01, second material:-0.96, p < 0.001) and overall image quality (first material:-0.59, p < 0.05, second materi-al::-1.26, p < 0.001). For ADMIRE 3, an early positive attitude for the algorithm was noted, with no significant change over time for all criteria except one (overall image quality), where a significant negative trend over time (-1.08, p < 0.001) was seen in the second material.Conclusions: With progression of reviews in both materials, an increasing dislike for ADMIRE 5 images was apparent for two image criteria. In this time perspective (weeks or months), no learning effect towards accepting the algorithm could be demonstrated.
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| 45. |
- Kataria, Bharti, 1955-
(författare)
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Visual grading evaluation of reconstruction methods and dose optimisation in abdominal Computed Tomography
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since its introduction in the 1970’s CT has emerged as a modality of choice because of its high sensitivity in producing accurate diagnostic images. A third of all Computed Tomography (CT) examinations are abdominal CTs which deliver one of the highest doses among common examinations. An increase in the number of CT examinations has raised concerns about the negative effects of ionising radiation as the dose is cumulative over the life span of the individual. Image quality in CT is closely related to the radiation dose, so that a certain dose with an associated small, but not negligible, risk is a prerequisite for high image quality. Typically, dose reduction in CT results in higher noise and a decrease in low contrast resolution which can be detrimental to the image quality produced. New technology presents a wide range of dose reduction strategies, the latest being iterative reconstruction (IR).The aim of this thesis was to evaluate two different classes of iterative reconstruction algorithms: statistical (SAFIRE) and model-based (ADMIRE) as well as to explore the diagnostic value of a low-dose abdominal CT for optimisation purposes.This thesis included a total of 140 human subjects in four image quality evaluation studies, three of which were prospective studies (Papers I, II and IV) and one retrospective study (Paper III). Visual grading experiments to determine the potential dose reductions, were performed with pairwise comparison of image quality in the same patient at different tube loads (dose) and reconstructed with Filtered back projection (FBP) and SAFIRE strength 1 in a low-dose abdominal CT (Paper I) and FBP and ADMIRE strengths 3 and 5 in a standard dose abdominal CT (Paper II). Paper IV evaluated the impact of slice thicknesses in CT images reconstructed with ADMIRE strengths 3 and 5 when comparing multiplanar reconstruction (MPR) formatted images in a standard dose abdominal CT. Paper III, on the other hand, was an absolute assessment of image quality and pathology between the three phases of a CT Urography (CTU) protocol to explore the diagnostic value of low-dose abdominal CT. The anonymised images were displayed in random order and image quality was assessed by a group of radiologists using image quality criteria from the “European guidelines of quality criteria for CT”. The responses from the reviewer assessment were analysed statistically with ordinal logistic regression i.e. Visual Grading Regression (VGR).Results in Paper I show that a small dose reduction (5-9 %) was possible using SAFIRE strength 1and indicated the need for further research to evaluate the dose reduction potential of higher strengths of the algorithm. In Paper II a 30% dose reduction was possible without change in ADMIRE algorithm strength as no improvement in image quality was observed between tube loads 98- and 140 mAs. When comparing tube loads 42 and 98 mAs, further dose reduction was possible with ADMIRE strength 3 (22-47%). However, for images reconstructed with ADMIRE strength 5, a dose reduction of 34-74% was possible for some, but not all image criteria. Image quality in low-contrast objects such as the liver parenchyma, was affected and a decline in diagnostic confidence was observed. Paper IV showed potential dose reductions are possible with increasing slice thickness from 1 mm to 2 mm (24-35%) and 1 mm to 3mm (25-41%). ADMIRE strength 3 continued to provide diagnostically acceptable images with possible dose reductions for all image criteria assessed. Despite objective evaluations showing a decrease in noise and an increase in contrast to noise ratio, ADMIRE strength 5 had diverse effects on the five image criteria, depending on slice thickness and further dose reductions were limited to certain image criteria. The findings do not support a general recommendation to replace ADMIRE3 with ADMIRE5 in clinical abdominal CT protocols.Paper III studied another aspect of optimisation and results show that visualisation of renal anatomy was as expected in favour of the post-contrast phases when compared to the native phase. Assessment of pathology showed no significant differences between the three phases. Significantly higher diagnostic certainty for renal anatomy was observed for the post-contrast phases when compared to the native phase. Significantly high certainty scores were also seen for the nephrographic phase for incidental findings. The conclusion is that a low-dose series seems to be sufficient as a first-line modality in certain patient groups.This thesis clinically evaluated the effect of IR in abdominal CT imaging and estimated potential dose reductions. The important conclusion from papers I, II and IV is that IR improves image quality in abdominal CT allowing for some dose reductions. However, the clinical utility of the highest strength of the algorithm is limited to certain criteria. The results can be used to optimise the clinical abdominal CT protocol. The conclusion from paper III may increase clinical awareness of the value of the low-dose abdominal protocol when choosing an imaging method for certain patient groups who are more sensitive to radiation.
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| 46. |
- Klintström, Eva, et al.
(författare)
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Trabecular bone microstructure analysis on data from a novel twin robotic X-ray device
- 2023
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Ingår i: Acta Radiologica. - : SAGE Publications. - 0284-1851 .- 1600-0455. ; 64:4, s. 1566-1572
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Tidskriftsartikel (refereegranskat)abstract
- Background: Bone strength is related to both mineral density (BMD) and the bone microstructure. However, only the assessment of BMD is available in clinical routine care today. Purpose: To analyze and study the correlation of trabecular bone microstructure from the imaging data of a prototype Multitom Rax system, using micro-computed tomography (CT) data as the reference method (Skyscan 1176).Material and Methods: Imaging data from 14 bone samples from the human radius were analyzed regarding six bone structure parameters, i.e. trabecular nodes, separation, spacing, and thickness as well as bone volume (BV/TV) and structural model index (SMI).Results: All six structure parameters showed strong correlations to micro-CT with Spearman correlation coefficients in the range of 0.83–0.93. BV/TV and SMI had a correlation >0.90. Two of the parameters, namely, separation and number, had mean values in the same range as micro-CT. The other four were either over- or underestimated.Conclusion: The strong correlation between micro-CT and the clinical imaging system, indicates the possibility for analyzing bone microstructure with potential to add value in fracture assessment using the studied device in a clinical workflow.
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| 47. |
- Larsson, Peter, et al.
(författare)
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Transmission ionization chambers for measurements of air collision kerma integrated over beam area. Factors limiting the accuracy of calibration
- 1996
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 41:11, s. 2381-2398
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Tidskriftsartikel (refereegranskat)abstract
- Kerma - area product meters (KAP meters) are frequently used in diagnostic radiology to measure the integral of air-collision kerma over an area perpendicular to the x-ray beam. In this work, a precise method for calibrating a KAP meter to measure is described and calibration factors determined for a broad range of tube potentials (40 - 200 kV). The integral is determined using a large number of TL dosimeters spread over and outside the nominal field area defined as the area within 50% of maximum . The method is compared to a simplified calibration method which approximates the integral by multiplying the kerma in the centre of the field by the nominal field area . While the calibration factor using the precise method is independent of field area and distance from the source, that using the simplified method depends on both. This can be accounted for by field inhomogeneities caused by the heel effect, extrafocal radiation and scattered radiation from the KAP meter. The deviations between the calibration factors were as large as for collimator apertures of and distances from the source of 50 - 160 cm. The uncertainty in the calibration factor using the precise method was carefully evaluated and the expanded relative uncertainty estimated to be with a confidence level of 95%.
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| 48. |
- Lindström, Jan, et al.
(författare)
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Development and assessment of a quality assurance device for radiation field-light field congruence testing in diagnostic radiology
- 2020
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Ingår i: Journal of Medical Imaging. - : SPIE - International Society for Optical Engineering. - 2329-4302 .- 2329-4310. ; 7:6
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Existing methods for checking the light field-radiation field congruence on x-ray equipment either do not fully meet the conditions of various quality control standards regarding inherent uncertainty requirements or contain subjective steps, further increasing the uncertainty of the end result. The aim of this work was to develop a method to check the light field-radiation field congruence on all x-ray equipment. The result should have a low uncertainty which is accomplished by eliminating most subjective user steps in the method. A secondary aim was to maintain the same level of usability as of comparable methods but still able to store the result. Approach: A new device has been developed where the light field and corresponding radiation field are monitored through measurements of the field edge locations (in total: 2 x 4 edges). The maximum field size location deviation between light field and radiation field in the new method is constrained by the physical limitations of the sensors used in various versions of the prototype: linear image sensors (LISs) of 25 to 29 mm active sensor length. The LISs were sensitized to x-rays by applying a phosphor strip of Gd2O2S: Tb covering the light sensor input area. Later prototypes of the completed LIS device also have the option of a Bluetooth (100-m range standard) connection, thus increasing the mobility. Results: The developed device has a special feature of localization a field edge without any prior, subjective, alignment procedure of the user, i.e., the signals produced were processed by software storing the associated field edge profiles, localizing the edges in them, and finally displaying the calculated deviation. The uncertainty in field edge location difference was estimated to be <0.1 mm (k = 2). The calculated uncertainty is lower than for other, commercially available, methods for light field-radiation field congruence also presented in this work. Conclusions: A method to check the light field-radiation field congruence of x-ray systems was developed to improve the limitations found in existing methods, such as device detector resolution, subjective operator steps, or the lack of storing results for later analysis. The development work overcame several challenges including mathematically describing real-life edges of light and radiation fields, noise reduction of radiation edges, and mapping/quantification of the rarely observed phenomenon of focal spot wandering. The assessment of the method showed that the listed limitations were overcome, and the aims were accomplished. It is therefore believed that the device can improve the work in quality controls of x-ray systems.
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| 49. |
- Lindström, Jan, et al.
(författare)
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Experimental verification of a model for estimating the particle size dependence of extrinsic efficiency of radioluminescent layers
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The extrinsic (absolute) efficiency of a phosphor is expressed as the ratio of light energy emitted per unit area at the phosphor surface to incident x-ray energy fluence. Several studies on polycrystalline phosphor materials show that the optical parameters of a specific phosphor may vary within a wide range of values. The aim of this work was to verify a previously published model where all optical parameters were replaced with a single parameter, the light extinction factor ξ. The varying extrinsic efficiency for an extended range of particle sizes and layer thicknesses are calculated from the input parameters: the intrinsic efficiency η, the mean particle size of the phosphor, the thickness of the layer, the light extinction factor and the calculated energy imparted to the layer. The X-ray spectrum was simulated utilising the SpekCalc software (Poludniowski et al 2009). In this work, calculations of the energy imparted to in-house manufactured Gd2O2S:Tb screens, were also compared to calculations improved making use of Monte Carlo simulations (software PENELOPE (Baro et al 1995)). KAP (kerma area product) -rate-values were noted and the corresponding luminance measured and compared to calculated values. The deviations were ±14 % within the studied range.
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| 50. |
- Lindström, Jan, et al.
(författare)
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Optimizing two radioluminescence based quality assurance devices for diagnostic radiology utilizing a simple model
- 2014
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Ingår i: Medical Imaging 2014. - : SPIE - International Society for Optical Engineering. ; , s. 90333R-1-90333R-15
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Konferensbidrag (refereegranskat)abstract
- The extrinsic (absolute) efficiency of a phosphor is expressed as the ratio of light energy emitted per unit area at the phosphor surface to incident x-ray energy fluence. A model described in earlier work has shown that by knowing the intrinsic efficiency, the particle size, the thickness and the light extinction factor ξ, it is possible to deduce the extrinsic efficiency for an extended range of particle sizes and layer thicknesses for a given design. The model has been tested on Gd 2O2S:Tb and ZnS:Cu fluorescent layers utilized in two quality assurance devices, respectively, aimed for the assessment of light field and radiation field congruence in diagnostic radiology. The first unit is an established device based on both fluorescence and phosphorescence containing an x-ray sensitive phosphor (ZnS:Cu) screen comprising a long afterglow. Uncertainty in field edge position is estimated to 0.8 mm (k=2). The second unit is under development and based on a linear CCD sensor which is sensitized to x-rays by applying a Gd 2O2S:Tb scintillator. The field profiles and the corresponding edge location are then obtained and compared. Uncertainty in field edge location is estimated to0.1 mm (k=2). The properties of the radioluminescent layers are essential for the functionality of the devices and have been optimized utilizing the previously developed and verified model. A theoretical description of the maximization of phosphorescence is also briefly discussed as well as an interesting finding encountered during the development processes: focal spot wandering. The oversimplistic physical assumptions made in the radioluminescence model have not been found to lead the optimizing process astray. The obtained functionality is believed to be adequate within their respective limitations for both devices.
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