| 1. |
- Ahle, Margareta, 1966-
(författare)
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Necrotising Enterocolitis : epidemiology and imaging
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Necrotising enterocolitis (NEC) is a potentially devastating intestinal inflammation of multifactorial aetiology in premature or otherwise vulnerable neonates. Because of the broad spectrum of presentations, diagnosis and timing of surgical intervention may be challenging, and imaging needs to be an integrated part of management.The first four studies included in this thesis used routinely collected, nationwide register data to describe the incidence of NEC in Sweden 1987‒2009, its variation with time, seasonality, space-time clustering, and associations with maternal, gestational, and perinatal factors, and the risk of intestinal failure in the aftermath of the disease.Early infant survival increased dramatically during the study period. The incidence rate of NEC was 0.34 per 1,000 live births, rising from 0.26 per 1,000 live births in the first six years of the study period to 0.57 in the last five. The incidence rates in the lowest birth weights were 100‒160 times those of the entire birth cohort. Seasonal variation was found, as well as space-time clustering in association with delivery hospitals but not with maternal residential municipalities.Comparing NEC cases with matched controls, some factors, positively associated with NEC, were isoimmunisation, fetal distress, caesarean section, persistent ductus arteriosus, cardiac and gastrointestinal malformations, and chromosomal abnormalities. Negative associations included maternal pre-eclampsia, maternal urinary infection, and premature rupture of the membranes. Intestinal failure occurred in 6% of NEC cases and 0.4% of controls, with the highest incidence towards the end of the study period.The last study investigated current practices and perceptions of imaging in the management of NEC, as reported by involved specialists. There was great consensus on most issues. Areas in need of further study seem mainly related to imaging routines, the use of ultrasound, and indications for surgery.Developing alongside the progress of neonatal care, NEC is a complex, multifactorial disease, with shifting patterns of predisposing and precipitating causes, and potentially serious long-term complications. The findings of seasonal variation, spacetime clustering, and negative associations with antenatal exposure to infectious agents, fit into the growing understanding of the central role of bacteria and immunological processes in normal maturation of the intestinal canal as well as in the pathogenesis of NEC. Imaging in the management of NEC may be developed through future studies combining multiple diagnostic parameters in relation to clinical outcome.
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| 2. |
- Blystad, Ida, 1972-
(författare)
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Clinical Applications of Synthetic MRI of the Brain
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Magnetic Resonance Imaging (MRI) has a high soft-tissue contrast with a high sensitivity for detecting pathological changes in the brain. Conventional MRI is a time-consuming method with multiple scans that relies on the visual assessment of the neuroradiologist. Synthetic MRI uses one scan to produce conventional images, but also quantitative maps based on relaxometry, that can be used to quantitatively analyse tissue properties and pathological changes. The studies presented here apply the use of synthetic MRI of the brain in different clinical settings.In the first study, synthetic MR images were compared to conventional MR images in 22 patients. The contrast, the contrast-to-noise ratio, and the diagnostic quality were assessed. Image quality was perceived to be inferior in the synthetic images, but synthetic images agreed with the clinical diagnoses to the same extent as the conventional images.Patients with early multiple sclerosis were analysed in the second study. In patients with multiple sclerosis, contrast-enhancing white matter lesions are a sign of active disease and can indicate a need for a change in therapy. Gadolinium-based contrast agents are used to detect active lesions, but concern has been raised regarding the long-term effects of repeated use of gadolinium. In this study, relaxometry was used to evaluate whether pre-contrast injection tissue-relaxation rates and proton density can identify active lesions without gadolinium. The findings suggest that active lesions often have relaxation times and proton density that differ from non-enhancing lesions, but with some overlap. This makes it difficult to replace gadolinium-based contrast agent injection with synthetic MRI in the monitoring of MS patients.Malignant gliomas are primary brain tumours with contrast enhancement due to a defective blood-brain barrier. However, they also grow in an infiltrative, diffuse manner, making it difficult to clearly delineate them from surrounding normal brain tissue in the diagnostic workup, at surgery, and during follow-up. The contrast-enhancing part of the tumour is easily visualised, but not the diffuse infiltration. In studies three and four, synthetic MRI was used to analyse the peritumoral area of malignant gliomas, and revealed quantitative findings regarding peritumoral relaxation changes and non-visible contrast enhancement suggestive of non-visible infiltrative tumour growth.In conclusion, synthetic MRI provides quantitative information about the brain tissue and this could improve the diagnosis and treatment for patients.
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| 3. |
- Carina, Stenman, 1964-
(författare)
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Standardized ultrasonography with cine-loop documentation : diagnostic variability in liver and kidney examinations
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: Ultrasound examination of the abdomen is often a first choice at radiology departments due to the lack of ionizing radiation. For diagnostic accuracy and economic benefits there has been a need for new routines in this area that incorporate the benefits of an radiographer or sonographer performing a multitude of ultrasound examinations following strictly standardized examination protocols and documentation forms made by cine-loops that will give the radiologist access to all relevant information needed for an accurate postexamination diagnosis.Aim: The overall objective of this thesis was to evaluate the diagnostic variability in examinations of the kidneys and liver that use a standardized ultrasound method along with video documentation of the entire examination and off-line review by radiologists. More specifically, we wanted to compare the agreement between readers and between operators.Design and method: This thesis is based on four quantitative studies using standardized protocols for kidney, liver and gallbladder examinations. In paper I, including 64 patients, and paper IV, including 98 patients, the patients were prospectively enrolled and the examinations were retrospectively reviewed. The patients in papers I and IV were examined by one radiographer (sonographer) and one radiologist during the same session. In paper I, findings using the standardized ultrasound method were compared with traditional bedside assessments by a radiologist. In paper IV, the patients were examined using only the standardized method. In paper II, including 98 patients, and in paper III, including 115 patients, the patients were examined by one sonographer using the standardized method and the examinations were reviewed by two or three radiologists.Results: In paper I, no significant systematic differences were found between the findings using the standardized method and the traditional bedside assessment.Paper II showed good intra- and inter-observer agreement between three experienced radiologists when reviewing examinations conducted using the standardized method.In paper III we verified good inter-observer agreement between two radiologists reviewing ultrasound examinations using the standardized technique in patients who had undergone surgery for colorectal cancer. Intravenous contrast was used and the injection of contrast medium increased the visibility of liver lesions.In paper IV, we observed that using a standardized cine-loop technique, there was a slightly better inter-operator agreement than inter-reader agreement.Conclusion: The satisfactory agreement shown in all four studies suggests that the new workflow method using standardized ultrasound examinations and stored cine-loops, performed by a radiographer or sonographer and analyzed off-line by a radiologist, is a promising technique. The results are less affected when a radiologist examiner is replaced by a radiographer or sonographer than when the reviewer is replaced by a different radiologist.
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| 4. |
- 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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| 5. |
- Klintström, Eva, 1957-
(författare)
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Image Analysis for Trabecular Bone Properties on Cone-Beam CT Data
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Trabecular bone structure as well as bone mineral density (BMD) have impact on the biomechanical competence of bone. In osteoporosis-related fractures, there have been shown to exist disconnections in the trabecular network as well as low bone mineral density. Imaging of bone parameters is therefore of importance in detecting osteoporosis. One available imaging device is cone-beam computed tomography (CBCT). This device is often used in pre-operative imaging of dental implants, for which the trabecular network also has great importance.Fourteen or 15 trabecular bone specimens from the radius were imaged for conducting this in vitro project.The imaging data from one dual-energy X-ray absorptiometry (DXA), two multi-slice computed tomography (MSCT), one high-resolution peripheral quantitative computed tomography (HR-pQCT) and four CBCT devices were segmented using an in-house developed code based on homogeneity thresholding. Seven trabecular microarchitecture parameters, as well as two trabecular bone stiffness parameters, were computed from the segmented data. Measurements from micro-computed tomography (micro-CT) data of the same bone specimens were regarded as gold standard.Correlations between MSCT and micro-CT data showed great variations, depending on device, imaging parameters and between the bone parameters. Only the bone-volume fraction (BV/TV) parameter was stable with strong correlations. Regarding both HR-pQCT and CBCT, the correlations to micro-CT were strong for bone structure parameters as well as bone stiffness parameters. The CBCT device 3D Accuitomo showed the strongest correlations, but overestimated BV/TV more than three times compared to micro-CT. The imaging protocol most often used in clinical imaging practice at our clinic demonstrated strong correlations as well as low radiation dose.CBCT data of trabecular bone can be used for analysing trabecular bone properties, like bone microstructure and bone biomechanics, showing strong correlations to the reference method of micro-CT. The results depend on choice of CBCT device as well as segmentation method used. The in-house developed code based on homogeneity thresholding is appropriate for CBCT data. The overestimations of BV/TV must be considered when estimating bone properties in future clinical dental implant and osteoporosis research.
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| 6. |
- Nordanskog, Pia, 1971-
(författare)
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On electroconvulsive therapy in depression : Clinical, cognitive and neurobiological aspects
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electroconvulsive therapy (ECT) is used worldwide to treat severe mental disorders. The most common mental disorder, and the third leading cause of disease burden in the world is depression. The clinical efficacy of ECT for severe depression is well-established. However, both the pathophysiology of depression and the mechanism of action of ECT remain elusive.The main aims of this thesis are to address the following issues: 1) the use and practice of ECT in Sweden has not been systematically evaluated since 1975, 2) cognitive side-effects (memory disturbances) are a major concern with ECT and 3) the mechanism of action of ECT remain elusive. The neurobiological aspects of ECT focus on two hypotheses. First, the recent years´ preclinical studies that have provided evidence that ECT induces hippocampal cell proliferation, including neurogenesis. Second, that enhanced functional inhibition of neuronal activity is a key feature.Current use and practice of ECT in Sweden (paper I) is based on data from the national quality register for ECT, the mandatory patient register of the National Board of Health and Welfare and a survey. Treated person rate (TPR) in Sweden 2013 was found to be 41 individuals / 100 000, and thus unchanged since the latest systematic investigation in Sweden 1975. In more than 70% of treatment series the indication was a depressive episode. The selection of patients for ECT and treatment technique in Sweden was similar to that in other western countries, but the consent procedure and the involvement of nurses and nursing assistants in the delivery of ECT differ. Data also shows that there is room for improvement in both the specificity of use and availability of ECT.The second study in this thesis is a longitudinal observational trial where 12 (paper II and III) and 14 (paper IV) patients with depression referred for ECT were investigated. Patients underwent a 3 T MRI structural scanning and DSC-MRI perfusion, a neuropsychological test battery and clinical ratings before ECT, within one to two weeks after ECT and after 6 and 12 months. In line with preclinical findings and the plasticity hypothesis of mechanism of action of ECT, the hippocampal volume increased after ECT in patients with depression. However, this increase was transient and returned to baseline levels within 6 months. No correlation was found between volumetric changes and clinical effect or cognitive outcome. Instead our results suggested an association to the number of treatments, without relation to the side of stimulation. A right-sided decrease in frontal blood flow distinguished remission from non-remission after ECT. There were significant impairments in verbal episodic memory and verbal fluency within one week after ending the ECT course, but these impairments were transient and no persistent cognitive impairments were seen during the follow-up.In summary, this thesis present the first update on the use and practice of ECT in Sweden in the last 40 years as well as a pioneering MRI-study on the hippocampal volume increase in the treatment of depression with ECT. Supportive to earlier findings we also found the cognitive side-effects that are measurable after ECT to be transient. Furthermore, we found that a decreased frontal blood flow is of importance for the anti-depressive response to ECT.
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| 7. |
- Persson, Anders, 1953-
(författare)
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Volume imaging of the abdomen : three-dimensional visualisation of tubular structures in the body with CT and MRI
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overwhelming amount of image-based information in modem medicine makes it crucial to develop methods to handle and analyze images and make them comprehensible for users. The aim of this thesis was to study the radiological practice of three-dimensional (3D) visualization of tubular structures in the body with CT and MRI. All the studies cancern 3D imaging of tubular structures with camputed tomography (CT) and magnetic resonance imaging (MRI). The first three studies examine the abdominal aorta; the two later ones the, bile ducts.Study I compared measurements of aorta diameters taken from MR images presented using two visualization methods - maximum intensity projection (MlP) and volume rendering (VRT) - with invasive angiography (DSA) and CT as reference methods. Mean diameters of MR images were smaller than those from DSA and CT when MlP was used, but in general not when VRT was used.Study II evaluated the dependence on the observer and the choice of method and settings during rendering using the same material as in Study 1. In both MlP and VRT, the choice of settings had significant influence on the results. With DSA as the reference method, VRT gave larger measurement errors than MIP when the rendering parameters were set to fixed values, but not if the user was allowed to select the settings freely.Study III evaluated three new techniques for standardizing VRT protocols for MRA. Inter-reader variability and agreement with DSA were studied by comparing diameter measurements of the abdominal aorta obtained by the three new techniques, by VRT with freely chosen parameters and by MlP. All three new methods were significantly better than MlP and VRT with freely chosen parameters conceming inter-observer agreement. Agreement with DSA was significantly better for one of the methods. Standardized protocols seem to have a potential to make VRT a clinically useful alternative to MlP for MR angiography measurements.Study IV evaluated CT imaging of the bile ducts after drip intravenous infusion of the contrast medium iotroxate (CT cholangiography) in terms of adverse effects and visibility. With infusion time adjusted for individual variation in serum bilirubin concentration, a total side-effect frequency of less than 1% was found. A systematic review of previously published studies indicated a frequency of 2.3%. Good contrast excretion and visualization of bile ducts even in patients with elevated bilirubin levels were noted.Study V evaluated the diagnostic benefits of the same imaging method by comparing it with findings from surgery and endoscopic retrograde cholangiopancreatography (ERCP). The consensus sensitivity and specificity for diagnosing biliary stones was 88% and 94%, respectively. The use of VRT improved diagnostic certainty in 14% of the evaluatians, and the visualization of ductal stones was improved in 38% of the positive cases.In conclusion, volume rendering technique with standardized parameters may become a clinically useful tool in the clinical MRI environment. DIC-CT with bilirubin-governed infusion time and volume rendering post-processing produces detailed images of the biliary tree, resulting in good sensitivity and specificity. Moreover the safety is acceptable.
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| 8. |
- Ragnehed, Mattias, 1976-
(författare)
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Functional Magnetic Resonance Imaging for Clinical Diagnosis : Exploring and Improving the Examination Chain
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Functional Magnetic Resonance Imaging (fMRI) is a relatively new imaging technique, first reported in 1992, which enables mapping of brain functions with high spatial resolution. Functionally active areas are distinguished by a small signal increase mediated by changes in local blood oxygenation in response to neural activity. The ability to non-invasively map brain function and the large number of MRI scanners quickly made the method very popular, and fMRI have had a huge impact on the study of brain function, both in healthy and diseased subjects.The most common clinical application of fMRI is pre-surgical mapping of brain functions in order to optimise surgical interventions. The clinical fMRI examination procedure can be divided into four integrated parts: (1) patient preparation, (2) image acquisition, (3) image analysis and (4) clinical decision. In this thesis, important aspects of all parts of the fMRI examination procedure are explored with the aim to provide recommendations and methods for prosperous clinical usage of the technique.The most important results of the thesis were: (I) administration of low doses of diazepam to reduce anxiety did not invalidate fMRI mapping results of primary motor and language areas, (II) the choice of visual stimuli equipment can have severe impact on the mapping of visual areas, (III) three-dimensional fMRI imaging sequences did not perform better than two-dimensional imaging sequences, (IV) adaptive spatial filtering can improve the fMRI data analysis, (V) clinical decisions should not be based on activation results from a single statistical threshold.
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| 9. |
- Tisell, Anders
(författare)
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The Non-Invasive Brain Biopsy : Implementation and Application of Quantitative Magnetic Resonance Spectroscopy on Healthy and Diseased Human Brain
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Introduction: In this thesis, one of the major objectives was to implement a method for (absolute) quantitative magnetic resonance spectroscopy (qMRS) of the human brain, intended for clinical use. The implemented method was based on standard spatially selective MRS sequences. The tissue water was used as an internal reference, which was calibrated using whole brain quantitative magnetic resonance imaging (qMRI). The second objective was to apply the method in clinical neuroimaging investigation, of different disease processes in the human brain.Materials and Methods: In total, 158 subjects were included and 507 MRS measurements (330 in white matter and 177 in the thalamus) were acquired.In a cross-sectional study of multiple sclerosis (MS), 35 ‘clinically definite MS’ (CDMS) patients were included, of which 15 were atypical CDMS patients with a very low number of white matter lesions (two or fewer), and 20 were typical CDMS patients with white matter lesions (three or more) were included. The metabolite concentrations in normal appearing white matter (NAWM) and the thalamus were assessed using the qMRS method developed in this thesis, and the brain parenchymal fraction (BPF) was calculated from the qMRI data. A cohort of 27 CDMS patients were then treated with Natalizumab and examined both at baseline, and after one year of treatment. Both qMRS and CSF samples for the purpose of assessing intrathecal inflammation were obtained. In addition, the frontal deep white matter (FDWM) and the thalamus were investigated in 20 idiopathic normal pressure hydrocephalus (iNPH) patients using qMRS. Finally, the left thalamus of 14 Kleine-Levin Syndrome (KLS) patients were examined using both qMRS and functional MRI (fMRI) of neurological activation of the left thalamus during a working memory test. Moreover, 63 healthy subjects were included as controls for this work.Results: A quantitative MRS method based on water referencing was successfully developed, implemented, and evaluated at 1.5 T. Both healthy subjects and MS patients showed a positive correlation between the concentrations of total Creatine (tCr) and myo Inositol (mIns) and age, and also a negative correlation with BPF were observed. Glutamate and Glutamine (Glx) levels were elevated for all MS patient groups compared to healthy controls. In contrast, lower concentrations of total N-acetyl aspartate and N-acetyl aspartate glutamate (tNA) and higher mIns concentrations in NAWM were only observed in MS patients that had developed white matter lesions. Moreover, the change in concentrations of tCr and total Choline (tCho) in MS patients during Natalizumab-treatment were positively correlated with markers of intrathecal inflammation. The iNPH patients had lower tNA and N-acetyl aspartate (NAA) concentrations in the thalamus compared to the controls. In addition, the NAA concentrations in the left thalamus were inversely correlated to the fMRI activation in the left thalamus during the working memory test in KLS patients.Discussion: The calculated calibration factors were in good agreement with the results found in the literature, indicating that the calibration factors were accurate.The observed elevated Glx concentration in MS could be due to increased concentrations of glutamate (Glu), which is neurotoxic at high concentrations, thus the elevated Glx could be linked to the clinically observed neurodegeneration in MS both in patients that have developed lesions and in atypical patients that do not develop any (or extremely few) lesions.Both tCr and mIns can be used as glia markers, thus the correlations of tCr and mIns concentrations with both age and BPF indicates that the local glia cell density, or tissue fraction, increases with age and atrophy. Moreover, the higher mIns concentrations in the NAWM of MS patients with a substantial white matter lesion load indicate that the glia tissue amount in NAWM is increased in MS patients that develop lesions. NAA is neuronal-specific, thus the lower tNA concentrations indicate that the neurone concentration is lower in the NAWM of MS patients that develop MS lesions. The lack of correlation between tNA with age and BPF in combination with the presence of correlation between tCr and mIns with both age and BPF, might be explained using a model for neurodegeneration. In which, there is a higher neurone loss compared to the glia loss. However, the lost tissue is compensated by compression of the tissue, which keeps the density of neurones more or less constant and the density of glia increased.The low concentration levels of the neuronal marker NAA in the thalamus of the iNPH patients indicates that the basal ganglia-thalamic-subcortical frontal circuits are damage or at least strongly modulated in the thalamus.The correlation between strong activation in left thalamus during a working memory test with the neuronal marker NAA indicate that the KLS patients that have low neuronal concentration also needed to utilise the working memory circuitry more heavily in order to perform the task as healthy subjects.Conclusion: It is possible to use qMRI for accurate and robust determination of qMRS in clinical practice, even at 1.5 T field strength. The tGlx concentration may be an important marker for pathology in the nonlesional white matter of MS-patients. The increased glia and loss of neurones in the NAWM are associated with the formation of white matter lesions.
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| 10. |
- Wang, Chunliang, 1980-
(författare)
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Computer-Assisted Coronary CT Angiography Analysis : From Software Development to Clinical Application
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Advances in coronary Computed Tomography Angiography (CTA) have resulted in a boost in the use of this new technique in recent years, creating a challenge for radiologists due to the increasing number of exams and the large amount of data for each patient. The main goal of this study was to develop a computer tool to facilitate coronary CTA analysis by combining knowledge of medicine and image processing, and to evaluate the performance in clinical settings.Firstly, a competing fuzzy connectedness tree algorithm was developed to segment the coronary arteries and extract centerlines for each branch. The new algorithm, which is an extension of the “virtual contrast injection” (VC) method, preserves the low-density soft tissue around the artery, and thus reduces the possibility of introducing false positive stenoses during segmentation. Visually reasonable results were obtained in clinical cases.Secondly, this algorithm was implemented in open source software in which multiple visualization techniques were integrated into an intuitive user interface to facilitate user interaction and provide good overviews of the processing results. An automatic seeding method was introduced into the interactive segmentation workflow to eliminate the requirement of user initialization during post-processing. In 42 clinical cases, all main arteries and more than 85% of visible branches were identified, and testing the centerline extraction in a reference database gave results in good agreement with the gold standard.Thirdly, the diagnostic accuracy of coronary CTA using the segmented 3D data from the VC method was evaluated on 30 clinical coronary CTA datasets and compared with the conventional reading method and a different 3D reading method, region growing (RG), from a commercial software. As a reference method, catheter angiography was used. The percentage of evaluable arteries, accuracy and negative predictive value (NPV) for detecting stenosis were, respectively, 86%, 74% and 93% for the conventional method, 83%, 71% and 92% for VC, and 64%, 56% and 93% for RG. Accuracy was significantly lower for the RG method than for the other two methods (p<0.01), whereas there was no significant difference in accuracy between the VC method and the conventional method (p = 0.22).Furthermore, we developed a fast, level set-based algorithm for vessel segmentation, which is 10-20 times faster than the conventional methods without losing segmentation accuracy. It enables quantitative stenosis analysis at interactive speed.In conclusion, the presented software provides fast and automatic coronary artery segmentation and visualization. The NPV of using only segmented 3D data is as good as using conventional 2D viewing techniques, which suggests a potential of using them as an initial step, with access to 2D reviewing techniques for suspected lesions and cases with heavy calcification. Combining the 3D visualization of segmentation data with the clinical workflow could shorten reading time.
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