| 5401. |
- Herrmann, C., et al.
(författare)
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Simulation of nodule-like pathology in radiographs of the lumbar spine
- 2000
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Ingår i: Radiation Protection Dosimetry. - 1742-3406. ; 90:1-2, s. 113-116
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Tidskriftsartikel (refereegranskat)abstract
- For the evaluation of the imaging properties of medical radiographic systems there are well-established standards for measuring techniques available, e.g. ISO 9236 for the measurement of the H/D curve. However, such measuring techniques require sophisticated equipment which is not available in a clinical environment. For a clinical routine of image evaluation, techniques like contrast-detail diagrams or the visual inspection of radiographs of grid pattern with varying contrast and spatial resolution are very common. The disadvantage of these techniques is that the corresponding results are very hard to be transferred to real patient images. Therefore, observer studies on the detection of certain pathology are commonly used to e.g. investigate the influence of different radiographic techniques on diagnostic image quality. As it is very difficult to find a sufficient number of patients with real pathologies for such studies, the pathologies are often simulated by fixing e.g. aluminium disks or other nodule-like objects to healthy volunteers when the radiograph is produced. This approach is relatively simple and rather successful in chest imaging. For lumbar spine images, however, the situation is different because nodule-like tumours cannot only consist of bony material which is increasing the X-ray absorption, but tumours can also destroy the bone material resulting in an increased transparency of the corresponding anatomical region. Such a behaviour is extremely hard to be simulated by fixing an external object to the patient. However, it can be easily simulated in a computer and applied to digital radiographic data. The current paper presents a computer model for the simulation of nodules in lumbar spine images. The model has been applied within a CEC founded research project, which was investigating the influence of MTF and noise power spectra on the diagnostic quality of radiographs of the lumbar spine.
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| 5402. |
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| 5403. |
- Herrnsdorf, Lars, et al.
(författare)
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A method to characterize the radiation output from a cone beam O-arm using a device for dose and dose profile scanning measurement
- 2013
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Ingår i: Medical Imaging 2013: Physics of Medical Imaging. - : SPIE. - 0277-786X .- 1996-756X. - 9780819494429 ; 8668, s. 86682-86682
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Konferensbidrag (refereegranskat)abstract
- The O-arm system is a mobile intraoperative imaging system that is comprised of fluoroscopy and cone beam CT. The configuration of the O-arm system with absence of patient table and a broad beam width (165 mm in isocenter) brings new practical and physical requirements on how to perform dose measurements. The purpose of this study was to describe a method that overcomes this and makes it possible to characterize the radiation output from the O-arm system. A holder with a clamp and a flexible ball joint that can orientate the radiation detector support and the Mover that can be adjusted to hold the dose detector in a horizontal position was used. Evaluation of the dose response for three different dose detectors of different active length (0.3, 23.1 and 100 mm) was made for three different beam qualities. Furthermore the dose profile free in air to control the possible heel effect and width of the x-ray field during rotation was measured and the dose rate waveform was analyzed. The FWHM of the dose profile was 162 mm The dose response of the three detectors is reported. The average dose response was lower for the detector with longer active length due to the influence of the dose profile shape. From dynamic measurement total exposure time, pulse width, and the number of pulses were verified. In conclusion, an external horizontal hanging holder with mover option helps to assist to make dose measurement easier and enables characterize the radiation output from the O-arm system.
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| 5404. |
- Herrnsdorf, L., et al.
(författare)
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Beam quality correction factors for KAP meters for lightlyand heavily filtered X-ray beams
- 2016
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 169:1, s. 347-352
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Tidskriftsartikel (refereegranskat)abstract
- Kerma-area product (KAP) meters have a pronounced energy dependence when measuring air KAP for lightly filtered X-ray beams (RQR). Today, it is also common with more heavily filtered beams. In this work, the energy dependence for lightly as well as heavily filtered beams (RQC) was investigated for several KAP meter models. The relative energy dependence of the readings of an external and an internal KAP meter was determined relative to an ionisation chamber, which had been calibrated at the primary standards laboratory. As a complement to the measurements, the sensitivity of a KAP meter for various X-ray beam qualities was modelled using Monte Carlo simulations of photon transport and absorption. The result showed a variation in relative energy dependence of up to 30 %for KAP meters for RQC beam qualities compared with RQR qualities. A reduced sensitivity of KAP meters for heavily filtered beams in comparison with lightly filtered ones was found, and it is important that the beam-specific radiation quality correction factors are applied to correct the registered KAP values.
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| 5405. |
- Herrnsdorf, L., et al.
(författare)
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Optimization of energy and directional response of a small 4π silicon dosemeter for quality control of CT/CBCT-units – A 3D CAD, Monte-Carlo, AM approach
- 2020
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Ingår i: Applied Radiation and Isotopes. - : Elsevier BV. - 0969-8043. ; 158
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Tidskriftsartikel (refereegranskat)abstract
- A 4π radiation dosemeter for use in medical radiology was designed. It is based on a solid state silicon detector, a sensor wafer, a flex card, a 3D plastic holder and a spherical stainless steel filter with a distribution of holes around the detector. The detector is attached to the wafer using only low Z material. To achieve an energy and directional response which is as uniform as possible for various radiation qualities and beam directions, the filter was designed using a series of Monte Carlo calculations. The energy filter and its hole pattern were created using Additive Manufacturing (AM) in the form of metal 3D printing. The functionality of the dosemeter was designed to fulfill the quality criteria of a combined energy and angular dependence of less than 5% for the IEC beam qualities RQR and RQT in the range of 65–145 kV. This is a major improvement to the existing solutions that may need software corrections to be used for the same beam quality range.
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| 5406. |
- Herrnsdorf, Lars
(författare)
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Review of Methods to Control Patient Doses and Image Quality in Various CT Techniques
- 2012
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Ingår i: Medical Physics in the Baltic States. - 1822-5721. ; , s. 97-98
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Konferensbidrag (refereegranskat)abstract
- Medical X-ray imaging is the largest source of radiation exposure to the population from artificial sources. Computed tomography (CT) contributes with 50-80 % of that radiation. About 660 000 CT examinations (2005) are done in Sweden every year. A CT examination gives a mean effective dose of 5 mSv, which is about 10 times higher than for a corresponding conventional X-ray investigation. This presentation describes earlier, current and future dosimetric and image quality analysis methods, necessary to correspond to the rapidly developing CT-techniques.
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| 5407. |
- Herrnsdorf, L., et al.
(författare)
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Silicon photomultipliers for medical imaging and dosimetry-an overview
- 2016
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Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 169:1, s. 430-435
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Tidskriftsartikel (refereegranskat)abstract
- Silicon photomultipliers (SiPMs) are an enabling solid-state technology for low light sensing, with single photon sensitivity and photon number resolving capability. They feature an extremely high internal gain at the 106 level, comparable to photomultiplier tubes (PMTs), with the advantage of low operating voltage (~50 V compared to ~1000 V for PMT) and low energy consumption. The solid-state technology makes SiPMs compact, insensitive to magnetic fields and with an extreme flexibility in the design to cope with different applications. The fast development of the multiplication avalanche opens up the possibility to achieve time resolution at the 30 ps level. Dynamic range is however limited compared to PMT and the dark count rate relatively high, yet today at the level of 50 kHz/mm2 at room temperature. Interfaced with scintillation material, SiPMs provide a powerful platform for medical imaging applications (in positron emission tomography/computed tomography and in positron emission tomography/magnetic resonance), for X-ray quality control as well as for novel compact radiation protection instruments. This article gives an overview of SiPMs for medical imaging and dosimetry. In addition, a learning and training program targeted to graduate students is described.
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| 5408. |
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| 5409. |
- Heskamp, Sandra, et al.
(författare)
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Imaging of Human Epidermal Growth Factor Receptor Type 2 Expression with (18)F-Labeled Affibody Molecule Z(HER2:2395) in a Mouse Model for Ovarian Cancer
- 2012
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Ingår i: Journal of Nuclear Medicine. - : Society of Nuclear Medicine. - 0161-5505 .- 1535-5667 .- 2159-662X. ; 53:1, s. 146-153
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Tidskriftsartikel (refereegranskat)abstract
- Affibody molecules are small (7 kDa) proteins with subnanomolar targeting affinity. Previous SPECT studies in xenografts have shown that the Affibody molecule (111)In-DOTA-Z(HER2:2395) can discriminate between high and low human epidermal growth factor receptor type 2 (HER2)-expressing tumors, indicating that radiolabeled Affibody molecules have potential for patient selection for HER2-targeted therapy. Compared with SPECT, PET with positron-emitting radionuclides, such as (18)F, may improve imaging of HER2 expression because of higher sensitivity and improved quantification of PET. The aim of the present study was to determine whether the (18)F-labeled NOTA-conjugated Affibody molecule Z(HER2:2395) is a suitable agent for imaging of HER2 expression. The tumor-targeting properties of (18)F-labeled Z(HER2:2395) were compared with (111)In- and (68)Ga-labeled Z(HER2:2395) in mice with HER2-expressing SK-OV-3 xenografts. Methods: Z(HER2:2395) was conjugated with NOTA and radiolabeled with (18)F, (68)Ga, and (111)In. Radiolabeling with (18)F was based on the complexation of Al(18)F by NOTA. The 50% inhibitory concentration values for NOTA-Z(HER2:2395) labeled with (19)F, (69)Ga, and (115)In were determined in a competitive cell-binding assay using SK-OV-3 cells. Mice bearing subcutaneous SK-OV-3 xenografts were injected intravenously with radiolabeled NOTA-Z(HER2:2395). One and 4 h after injection, PET/CT or SPECT/CT images were acquired, and the biodistribution was determined by ex vivo measurement. Results: The 50% inhibitory concentration values for (19)F-, (69)Ga-, and (115)In-NOTA-Z(HER2:2395) were 5.0, 6.3, and 5.3 nM, respectively. One hour after injection, tumor uptake was 4.4 +/- 0.8 percentage injected dose per gram (% ID/g), 5.6 +/- 1.6 % ID/g, and 7.1 +/- 1.4 % ID/g for (18)F-, (68)Ga-, and (111)In-NOTA-Z(HER2:2395), respectively, and the respective tumor-to-blood ratios were 7.4 +/- 1.8, 8.0 +/- 1.3, and 4.8 +/- 1.3. Tumor uptake was specific, because uptake could be blocked efficiently by coinjection of an excess of unlabeled Z(HER2:2395). PET/CT and SPECT/CT images clearly visualized HER2-expressing SK-OV-3 xenografts. Conclusion: This study showed that (18)F-NOTA-Z(HER2:2395) is a promising new imaging agent for HER2 expression in tumors. Affibody molecules were successfully labeled with (18)F within 30 min, based on the complexation of Al(18)F by NOTA. Further research is needed to determine whether this technique can be used for patient selection for HER2-targeted therapy.
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| 5410. |
- Hesse, Bernhard, et al.
(författare)
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Accessing osteocyte lacunar geometrical properties in human jaw bone on the submicron length scale using synchrotron radiation mu CT
- 2014
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Ingår i: Journal of Microscopy. - : Wiley. - 0022-2720 .- 1365-2818. ; 255:3, s. 158-168
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Tidskriftsartikel (refereegranskat)abstract
- The architectural properties of the osteocyte cell network provide a valuable basis for understanding the mechanisms of bone remodelling, mineral homeostasis, ageing and pathologies. Recent advances in synchrotron microtomography enable unprecedented three-dimensional imaging of both the bone lacunar network and the extracellular matrix. Here, we investigate the three-dimensional morphological properties of osteocyte lacunae in human healthy and bisphosphonate-related osteonecrotic jaw bone based on synchrotron X-ray computed tomography images, with a spatial isotropic voxel size of 300 nm. Bisphosphonate-related osteonecrosis of the jaw is a relatively new disease with increasing incidence, which remains poorly understood. A step forward in elucidating this malady is to assess whether, and how, the morphology of the osteocyte lacunar network is modified in the affected jaw tissue. We evaluate thousands of cell lacunae from five specimens of which three originate from patients diagnosed with bisphosphonate-associated osteonecrosis. In this exploratory study, we report three-dimensional quantitative results on lacunar volumes (296-502 mu m(3)), shape (approximated by an ellipsoidal shape with principal axes a > b > c, such that a = 2.2b and a = 4c) and spatial distribution (i.e., 50% of the mineralized matrix volume is located within 12 mu m to the closest lacunar boundary) at submicron resolution on such specimens. We observe that the average lacunar volumes of the bisphosphonate-related osteonecrotic jaw specimens were within the range of volumes found in the two specimens originating from healthy donors and conclude that lacunar volumes are not the key element in the course of bisphosphonate-related osteonecrotic jaw. In three out of five specimens we observe lacunar volume sizes in segmented osteons to be significantly different compared to lacunar volumes in the adjacent tissue regions. Furthermore, we quantify the number of lacunae containing small dense objects (on average 9%). In contrast to lacunar morphology we report the lacunar density (16 000-50 000 per mm(3)) to be different in jaw bone tissue compared to what has been reported in femoral sites.
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