Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 129-135).

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 117-124).

Magnetic resonance imaging (MRI) is a highly exible and non-invasive medical imaging modality based on the concept of nuclear magnetic resonance (NMR). Compared to other imaging techniques, major limitation of MRI is the relatively long acquisition time. The slowness of acquisition makes MRI difficult to apply to time-sensitive clinical applications. Acquisition of MRA images with a spatial resolution close to conventional digital subtraction angiography is feasible, but at the expense of reduction in temporal resolution. Parallel MRI employs multiple receiver coils to speed up the MRI acquisition by reducing the number of data points collected. Although, the reconstructed images from undersampled data sets often suffer from different different types of degradation and artifacts. In contrast-enhanced magnetic resonance imaging, information is effectively measured in 3D k-space one line at a time therefore the 3D data acquisition extends over several minutes even using parallel receiver coils. This limits the assessment of high ow lesions and some vascular tumors in patients. To improve spatio-temporal resolution in contrast enhanced magnetic resonance angiography (CE-MRA), the use of incorporating prior knowledge in the image recovery process is considered in this thesis. There are five contributions in this thesis. The first contribution is the modification of generalized unaliasing using support and sensitivity encoding (GUISE). GUISE was introduced by this group to explore incorporating prior knowledge of the image to be reconstructed in parallel MRI. In order to provide improved time-resolved MRA image sequences of the blood vessels, the GUISE method requires an accurate segmentation of the relatively noisy 3D data set into vessel and background. The method that was originally used for definition of the effective region of support was primitive and produced a segmented image with much false detection because of the effect of overlying structures and the relatively noisy background in images. We proposed to use the statistical principle as employed for the modified maximum intensity projection (MIP) to achieve better 3D segmentation and optimal visualization of blood vessels. In comparison with the previous region of support (ROS), the new one enables higher accelerations MRA reconstructions due to the decreased volume of the ROS and leads to less computationally expensive reconstruction. In the second contribution we demonstrated the impact of imposing the Karhunen-Loeve transform (KLT) basis for the temporal changes, based on prior expectation of the changes in contrast concentration with time. In contrast with other transformation, KLT of the temporal variation showed a better contrast to noise ratio (CNR) can be achieved. By incorporating a data ordering step with compressed sensing (CS), an improvement in image quality for reconstructing parallel MR images was exhibited in prior estimate based compressed sensing (PECS). However, this method required a prior estimate of the image to be available. A singular value decomposition (SVD) modification of PECS algorithm (SPECS) to explore ways of utilising the data ordering step without requiring a prior estimate was extended as the third contribution. By employing singular value decomposition as the sparsifying transform in the CS algorithm, the recovered image was used to derive the data ordering in PECS. The preliminary results outperformed the PECS results. The fourth contribution is a novel approach for training a dictionary for sparse recovery in CE-MRA. The experimental results demonstrate improved reconstructions on clinical undersampled dynamic images. A new method recently has been developed to exploit the structure of the signal in sparse representation. Group sparse compressed sensing (GSCS) allows the efficient reconstruction of signals whose support is contained in the union of a small number of groups (sets) from a collection of pre-defined disjoint groups. Exploiting CS applications in dynamic MR imaging, a group sparse method was introduced for our contrast-enhanced data set. Instead of incorporating data ordering resulted from prior information, pre-defined sparsity patterns were used in the PECS recovery algorithm, resulting to a suppression of noise in the reconstruction.

<p>Atherosclerosis is a serious threat to public health and a major cause of morbidity and mortality. In this doctoral research, the feasibility of using whole-body magnetic resonance angiography (WBMRA) was studied as a principal aim both in patients and in an epidemiological setting. Secondary aims were to create a score for assessment of the degree of atherosclerosis with the use of WBMRA and to investigate the correlation between this score and various cardiovascular (CV) risk factors. </p><p>WBMRA was found feasible both in atherosclerotic patients and in an elderly population from the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS). All subjects except one completed the examination without any adverse events. A large proportion (93-99%) of the vessel segments could be evaluated and the results of a smaller comparison between WBMRA and conventional invasive x-ray angiography were reasonable regarding the assessed degree of maximum stenosis or occlusion. This indicates the safety and robustness of the WBMRA method.</p><p>Unsuspected significant vascular abnormalities were found in patients with atherosclerotic symptoms and significant vascular abnormalities were present in elderly subjects without any self-reported vascular disease. The prevalence rates of vascular abnormalities in the carotid, renal, and inflow and runoff arteries of the lower limbs were estimated in an elderly population. A total atherosclerotic score (TAS) reflecting the degree of luminal narrowing was created for the WBMRA method and was significantly related to Framingham risk score (FRS) and to the amount of abdominal visceral adipose tissue, interleukin-6, and leptin and was inversely significantly related to adiponectin. </p><p>Studies with outcome data of the PIVUS cohort are needed for further validation of the WBMRA method and to determine whether TAS can be used as an adjunct for CV risk assessment. Meanwhile, the correlation with FRS indicates that TAS could be of value for this purpose.</p>

Atherosclerosis is a serious threat to public health and a major cause of morbidity and mortality. In this doctoral research, the feasibility of using whole-body magnetic resonance angiography (WBMRA) was studied as a principal aim both in patients and in an epidemiological setting. Secondary aims were to create a score for assessment of the degree of atherosclerosis with the use of WBMRA and to investigate the correlation between this score and various cardiovascular (CV) risk factors. WBMRA was found feasible both in atherosclerotic patients and in an elderly population from the Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS). All subjects except one completed the examination without any adverse events. A large proportion (93-99%) of the vessel segments could be evaluated and the results of a smaller comparison between WBMRA and conventional invasive x-ray angiography were reasonable regarding the assessed degree of maximum stenosis or occlusion. This indicates the safety and robustness of the WBMRA method. Unsuspected significant vascular abnormalities were found in patients with atherosclerotic symptoms and significant vascular abnormalities were present in elderly subjects without any self-reported vascular disease. The prevalence rates of vascular abnormalities in the carotid, renal, and inflow and runoff arteries of the lower limbs were estimated in an elderly population. A total atherosclerotic score (TAS) reflecting the degree of luminal narrowing was created for the WBMRA method and was significantly related to Framingham risk score (FRS) and to the amount of abdominal visceral adipose tissue, interleukin-6, and leptin and was inversely significantly related to adiponectin. Studies with outcome data of the PIVUS cohort are needed for further validation of the WBMRA method and to determine whether TAS can be used as an adjunct for CV risk assessment. Meanwhile, the correlation with FRS indicates that TAS could be of value for this purpose.

Cardiovascular disease remains a leading a cause of mortality and morbidity. Primary prevention is known to reduce the incidence of cardiovascular disease. The use of medication is currently targeted at those at increased predicted risk of cardiovascular disease using risk prediction tools developed from large epidemiological studies. However these have poor external validity particularly for those at low or intermediate risk: a significant number of cardiovascular events still occurs in these groups. We hypothesised that screening for asymptomatic pre-clinical cardiovascular disease using B-type natriuretic peptide (BNP) and whole body contrast enhanced magnetic resonance imaging (MRI) could identify those at low/intermediate risk or disease whowill develop clinical disease and thus facilitate improved targeting of primary prevention at those most likely to benefit. The Tayside Screening for Cardiac Events (TASCFORCE) study is a prospective normal volunteer cohort study. Men and women aged 40 years or older free from cardiovascular disease and with a predicted 10-year coronary heart disease risk less than 20% were recruited. All had comprehensive baseline cardiovascular risk information and a BNP level measured. If the BNP level was greater than the median for their gender participants were invited to attend for a whole body contrast enhancedMRI scan comprising cardiac imaging and whole body angiography. The images were analysed to measure left ventricular mass (LVM), left ventricular volumes and left ventricular function. These were indexed for body size using height, height1.7, height2.7 and body surface area. Angiogram images were analysed for the presence and degree of intraluminal stenosis. All participants are being followed up using anonymised electronic data linkage for incident cardiovascular disease and death. 4423 participants (39.3% male) were recruited between November 2007 and February 2013. Median age was 51.2 years. The median 10-year coronary heart disease (CHD) 23 risk was 2% and 13.6% had a CHD risk of 10-19.9% (intermediate risk). The medianBNP results for men and women were 7.5 and 15.3 pg/ml respectively. Age, female sex and high density lipoprotein were independently associated with BNP level. Heart rate, total cholesterol and ex-smoking status were independently inversely associated with BNP level. 1528 (74.8% of those invited) underwent an MRI scan. Mean left ventricular mass was 129.2g and 87.0g for men and women respectively. LVM and left ventricular mass index (LVMI) were significantly higher in men than women. The vast majority (94.6%) of arterial segments analysed were normal and 50.6% of individuals had no evidence of luminal stenosis. From follow up data obtained 2 years after the end of recruitment 18,364 person years at risk were analysed. 17 cardiovascularevents and no deaths occurred in those not invited for an MRI scan based on their BNP result and 16 events and 1 death occurred in those invited for an MRI scan. There was no significant difference in event rates between those with above and below median BNP levels, between those with higher or lower LVM or LVMI or between those with and without the presence of stenosis on angiography. As expected we have not demonstrated the ability of LVM, LVMI or stenosis burden determined using magnetic resonance imaging to predict cardiovascular disease in a population at low or intermediate risk of CHD. We have also not demonstrated the ability of BNP to identify those at low orintermediate risk of CHD who will develop clinical CV disease. However it is the pre-planned longer-term follow up where difference might be expected. The low number of events at this early stage in follow up mean that it is difficult to draw firm conclusions. As follow up continues and further events accumulate we hope to determine if these measures will be shown to predict cardiovascular events in future analyses. We have characterised the normal values and distribution of a range of left ventricular structural and functional parameters derived using a steady state free precision sequence MRI in a population at low or intermediate risk of CHD which will provide a useful reference for normal values that are different to other imaging modalities including chocardiography and other protocols of MRI scanning.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-07-25T12:54:13Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Islane Cristina Martins.pdf: 2501962 bytes, checksum: f8da8fe4623e40c91559079d260f0d75 (MD5) / Made available in DSpace on 2017-07-25T12:54:13Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Islane Cristina Martins.pdf: 2501962 bytes, checksum: f8da8fe4623e40c91559079d260f0d75 (MD5) Previous issue date: 2016-08-26 / FACEPE / O círculo arterial cerebral é um polígono anastomótico na base do encéfalo que comunica o sistema carotídeo com o sistema vértebro-basilar e as carótidas entre si. Há muitas variações morfológicas nesse polígono e possíveis diferenças entre os sexos, particularmente no segmento A1 da artéria cerebral anterior e na origem da artéria cerebral posterior (ACP). O objetivo do presente estudo foi analisar comparativamente a frequência de hipoplasia do segmento A1 e do padrão fetal da artéria cerebral posterior no homem e na mulher. Foram analisadas retrospectivamente 848 angiografias por ressonância magnética arterial, em 426 homens e 422 mulheres, respectivamente, que se submeteram ao exame no Centro de Diagnóstico Multimagem. Os exames foram escolhidos aleatoriamente entre 1.000 angiorressonância realizadas entre 2010 e 2016, independente do motivo da solicitação médica. Hipoplasia do segmento A1 foi definido por analise qualitativa, quando havia uma nítida assimetria entre os dois segmentos A1 direito e esquerdo bem como o padrão fetal da artéria cerebral posterior. Para análise de hipoplasia foram medidos os diâmetros dos segmentos A1. Para análise do padrão fetal (diâmetro da ACP na origem da artéria carótida>diâmetro do segmento P1) foram analisadas 1.296 artérias carótidas em 648 indivíduos. Na análise estatística utilizouse o teste exato de Fisher. Os homens 152/326 (46,6%) apresentaram hipoplasia de A1 em comparação com 108/322 (33,5%) das mulheres (p<0,01, OR=1,7; IC95% 1,3-2,4). A hipoplasia de A1 nos homens foi mais frequente a direita (20% vs. 15%, p<0,01). O padrão fetal foi mais comum nas mulheres 151/644 (23,4%) do que em homens, 100/652 (15,3%) (p<0,001, OR=1,7; IC95% 1,3-2,2). As mulheres também apresentam mais padrão fetal bilateral do que os homens (8,0% vs. 3,4%; p<0,01; OR=0,4; IC 0,2-0,8). A hipoplasia do segmento A1 da artéria cerebral anterior é mais frequente nos homens e nas mulheres há uma maior frequência do padrão fetal da artéria cerebral posterior. / The Circle of Willis is an anastomotic polygon encephalon base that communicates the carotid system with vertebrobasilar system and carotid each other. There are lots of morphological variations that polygon and possible differences between genders particularly in the A1 segment of the anterior cerebral artery and the origin of the posterior cerebral artery (PCA) which are risk factors for anatomical brain aneurysms. The purpose of this study was to comparatively analyze the frequency of hypoplasia of the segment A1 and fetal type of cerebral posterior artery in man and woman. It was retrospectively reviewed 648 magnetic resonance angiographies in 326 men and 322 women, respectively. The tests were randomly chosen among about a thousand magnetic resonance angiographic performed between 2010 and 2016 in Multimagem Diagnostic Center, regardless of the medical reason request. Hypoplasia of the A1 segment was defined by qualitative analysis, when there was a clear asymmetry between the two segments A1, right and left. For hypoplasia analysis were also measured diameters of segments A1. For hypoplasia analysis were also measured diameters of segments A1. For analysis of the fetal type (diameter of the ACP origin of the carotid artery> diameter of the P1 segment of the ACP) were analyzed 1,296 carotid arteries (right and left) in 648 individuals. Statistical analysis was performed using Fisher's exact test. In men 152/326 (46.6%) showed hypoplasia A1 compared to 108/322 (33.5%) of women (p <0.01, OR = 1.7; 95% CI, 1.3-2, 4). Hypoplasia A1 was more common in men right (20% vs. 15%, p <0.01). Fetal type was more common in women 151/644 (23.4%) than in men (100/652; 15.3%) (p <0.001, OR = 1.7; 95% CI, 1.3-2, two). Women also have more bilateral fetal rate than men (8.0% vs. 3.4%; p <0.01). In conclusion, hypoplasia of the A1 segment of the anterior cerebral artery is more common in men and in women there is a greater frequency of fetal type of the posterior cerebral artery. Keywords: Circle of Willis

京都大学 / 新制・論文博士 / 博士(医学) / 乙第13436号 / 論医博第2235号 / 新制||医||1054(附属図書館) / (主査)教授 花川 隆, 教授 YOUSSEFIAN Shohab, 教授 髙橋 良輔 / 学位規則第4条第2項該当 / Doctor of Medical Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第21001号 / 医博第4347号 / 新制||医||1027(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 溝脇 尚志, 教授 辻川 明孝, 教授 小泉 昭夫 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

<p>In contrast-enhanced magnetic resonance angiography (CE-MRA),vascular signal is produced by the acquisition of a T1-weighted magnetic resonance imaging scan while the presence of a contrast agent induces a low T1 in blood. In this thesis,CE-MRA of the aortoiliac arteries was evaluated.Different contrast agents and techniques for synchronisation of the scan with the contrast bolus passage were assessed.</p><p>In 30 patients with clinically suspected iliac artery stenoses,contrast-enhanced magnetic resonance angiography was compared with duplex ultrasound scanning and digital subtraction x-ray angiography (DSA),with intraarterial pressure measurements as reference method. No statistically significant differences in sensitivity or specificity were observed between the techniques regarding the detection of hemodynamically significant iliac stenoses. The use of multiplanar reformats and source images in the MRA examinations was of value for the differentiation between high-grade stenoses and occlusions. With DSA as reference method, MRA had significantly higher sensitivity and specificity than duplex for the detection of ≥50% stenoses.</p><p>In fourteen patients examined with iliac artery MRA, differences in contrast arrival time of up to 7 s was observed between the aorta and the common femoral artery.A dual-station timing technique adjusting for this difference was found feasible. Compared with a fluoroscopically triggered technique (n=13),which is used in clinical rotine, the dual-station technique was more reliable for the visualisation of distal vessels.</p><p>In a clinical phase II study comparing different doses of t he contrast agent gadobenate dimeglumine for the enhancement of iliac artery MRA, a significant improvement in subjective diagnostic quality compared with time-of-flight MRA was found at all doses from 0.025 mmol/kg.An increasing trend with dose was observed up to a dose level of 0.05-0.1 mmol/kg.</p><p>In a phase I clinical study on the intravascular, iron oxide contrast agent NC100150 Injection, a positive dose response was observed for abdominal vascular enhancement, with the highest contrast-to-noise ratio observed at 4.0 mg Fe/kg bw at 1.5 T and at 2.5-4 mg Fe/kg bw at 0.5 T.At 1.5 T higher R2*values were calculated for the aorta than for the IVC.</p>