<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>

Despite the vast myriad of applications and the long way it has come, MRI is still a relatively new field of knowledge with much prospect for more advancement and expansion. This work is mainly concerned with two gradient echo imaging methods which are directly or indirectly related to blood vessel imaging as well as iron depiction in the human brain. In each case, new methods are introduced that overcome existing limitations. For blood vessel imaging, 3D Time-of-Flight (TOF) MR angiography (MRA) with its known capability to image arteries as well as veins was implemented at 3.0 T. At this field strength, the significant RF profile variability due to RF inhomogeneity is a liability for circle-of-Willis imaging in the human brain that was overcome by introducing a new means to counter the RF effects through increased slope of the ramped pulse. In addition a new method is introduced for TOF MRA with two-in-one arterial and venous 3D TOF imaging to overcome the significant scan time overhead of a traditional second venous scan and for cutting down RF power utilization. Using this method, total scan time could be reduced by as much as 46% and specific absorption rate (SAR) due to spatial saturation could be reduced by as much as 92%. For iron sensitive imaging, Susceptibility Weighted Imaging (SWI) was developed at 4.7 T. The phase SWI method was used to visualize lesions in Multiple Sclerosis (MS) patients and was experimentally compared to the visibility on standard T2 weighting with results demonstrating visualization of new lesions, with 18% of total lesions exclusively visible on SWI. A new approach to 3D imaging was also introduced to enable accurate oblique SWI scanning while overcoming the current restriction to axial imaging to produce correct phase effects for oblique imaging. New results from oblique phase imaging were presented and the phase measurements from key brain structures were successfully validated against images obtained by the current standard of axial imaging.

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. 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. 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. 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. 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.

In unstable coronary artery disease (CAD) it still is a matter of debate which patients should undergo early revascularisation. In the FRISC II study (n=2457) an early invasive strategy was, compared to a primarily non-invasive strategy, associated with reduced mortality and myocardial infarction (MI) rates. However, in this heterogeneous group of patients, tools for an appropriate selection to revascularisation are needed. From the FRISC II study we evaluated the prognosis, the angiographic extent of CAD and the effects of an early invasive strategy in relation to risk variables on admission. The occurrence of ST depression and/or elevated levels of Troponin T were associated with a higher risk for death and MI, more severe CAD and also with a reduction of death or MI by the early invasive strategy. Elevated levels of the inflammatory markers C-reactive protein (CRP) and interleukin-6 (Il-6) were associated with a higher mortality but an unchanged MI rate. Elevated levels of Il-6, but not CRP, identified patients with a large reduction of mortality by the invasive strategy. Age ≥ 70 years, male gender, diabetes, previous MI, ST depression and elevated levels of troponin and markers of inflammation were independently associated with an adverse outcome. The FRISC-score was constructed using these 7 variables. At FRISC-score ≥ 5 an early invasive strategy markedly reduced mortality and MI, at FRISC–score 3-4 death/MI was reduced, whereas in patients with a FRISC-score 0-2 neither mortality nor death/MI was influenced. In unstable CAD, a non-invasive strategy seems justified only for patients at low risk, i.e. FRISC score &lt; 2. In patients with intermediate and high risk, i.e. FRISC-score ≥ 3, an early invasive strategy is recommended.

Three-dimensional rotational angiography (3D-RA) is an established method within the field of interventional neuroradiology. The method has also a great potential in other areas with a complicated arterial anatomy. The purpose of this study was firstly to develop an investigative protocol for 3D-RA in renal transplanted patients with threatening allograft failure in diagnosing stenosis in the transplanted renal artery; secondly the protocol was evaluated and compared with a modified protocol including reduced contrast medium load. Furthermore, the advantages of the 3D reconstructions compared to the angiographic images were evaluated, likewise if an extended angle of rotation reduced the artifacts in the 3D reconstructions. The two protocols were compared with regard to image quality and acute nephrotoxicity. The accuracy of Doppler ultrasonography and the result of percutaneous transluminal angioplasty (PTA) were also assessed. 3D-RA was consecutively performed in 57 renal transplanted patients with suspicion of renal artery stenosis. A significant stenosis was found in 49% of the patients. The 3D reconstructions profiled 43% of the transplant renal artery stenoses better than the angiographic images. An extended angle of rotation reduced the artifacts. There was no statistical difference regarding image quality between the two protocols, and the renal function was equally affected in both protocols. Doppler ultrasonography sensitivity was 100%; specificity was 48% and positive predictive value 67%. PTA had a technical success rate of 92% and a clinical success rate of 75% after 3 months. 3D-RA is a helpful supplement in cases with complicated vascular anatomy, especially when PTA may be indicated. The 3D reconstructions profile the course of the artery more frequently than the angiographic images and support PTA. The 3D reconstructions are degraded of artifacts. Sampling artifacts can be diminished by increased C-arm rotation and increased number of projections. The distortions caused by beam hardening remain to be solved.

<p>Research using mice and rats has gained interest because they are robust test beds for clinical drug development and are used to elucidate disease etiologies. Blood vessel visualization and blood flow measurements are important anatomic and physiologic indicators to drug/disease stimuli or genetic modification. Cardio-pulmonary blood flow is an important indicator of heart and lung performance. Small animal functional imaging provides a way to measure physiologic changes minimally-invasively while the animal is alive, thereby allowing for multiple measurements in the same animal with little physiologic perturbation. Current methods of measuring cardio-pulmonary blood flow suffer from some or all of these limitations-they produce relative measurements, are limited to global or whole animal or organ regions, do not provide vasculature visualization, limited to a few or singular samples per animal, are not able to measure acute changes, or are very invasive or requires animal sacrifice. The focus of this work was the development of a small animal x-ray imaging system capable of minimally invasive real-time, high resolution vascular visualization, and cardio-pulmonary blood flow measurements in the live animal. The x-ray technique used was digital subtraction angiography (DSA). This technique is a particularly appealing approach because it is easy to use, can capture rapid physiological changes on a heart beat-to-beat basis, and provides anatomical and functional vasculature information. This DSA system is special because it was designed and implemented from the ground up to be optimized for small animal imaging and functional measurements. This system can perform: 1) minimally invasive in vivo blood flow measurements, 2) multiple measurements in the same animal in a rapid succession (every 30 seconds-a substantial improvement over singular measurements that require minutes to acquire by the Fick method), 3) very high resolution (up to 46 micron) vascular visualization, 4) quantitative blood flow measurements in absolute metrics (mL/min instead of arbitrary units or velocity) and relative blood volume dynamics from discrete ROIs, and 5) relative mean transit time dynamics on a pixel-by-pixel basis (100 µm x 100 µm). The end results are 1) anatomical vessel time course images showing the contrast agent flowing through the vasculature, 2) blood flow information of the live rat cardio-pulmonary system in absolute units and relative blood volume information at discrete ROIs of enhanced blood vessels, and 3) colormaps of relative transit time dynamics. This small animal optimized imaging system can be a useful tool in future studies to measure drug or disease modulated blood flow dynamics in the small animal.</p> / Dissertation

Atherosclerosis is a systemic disease of the vessel wall that occurs in the aorta, carotid, coronary and peripheral arteries. Atherosclerotic plaques in coronary arteries may cause the narrowing (stenosis) or complete occlusion of the arteries and lead to serious results such as heart attacks and strokes. Medical imaging techniques such as X-ray angiography and computed tomography angiography (CTA) have greatly assisted the diagnosis of atherosclerosis in living patients. Analyzing and quantifying vessels in these images, however, is an extremely laborious and time consuming task if done manually. A novel image segmentation approach and a quantitative shape analysis approach are proposed to automatically isolate the coronary arteries and measure important parameters along the vessels. The segmentation method is based on the active contour model using the level set formulation. Regional statistical information is incorporated in the framework through Bayesian pixel classification. A new conformal factor and an adaptive speed term are proposed to counter the problems of contour leakage and narrowed vessels resulting from the conventional geometric active contours. The proposed segmentation framework is tested and evaluated on a large amount of 2D and 3D, including synthetic and real 2D vessels, 2D non-vessel objects, and eighteen 3D clinical CTA datasets of coronary arteries. The centerlines of the vessels are proposed to be extracted using harmonic skeletonization technique based on the level contour sets of the harmonic function, which is the solution of the Laplace equation on the triangulated surface of the segmented vessels. The cross-sectional areas along the vessels can be measured while the centerline is being extracted. Local cross-sectional areas can be used as a direct indicator of stenosis for diagnosis. A comprehensive validation is performed by using digital phantoms and real CTA datasets. This study provides the possibility of fully automatic analysis of coronary atherosclerosis from CTA images, and has the potential to be used in a real clinical setting along with a friendly user interface. Comparing to the manual segmentation which takes approximately an hour for a single dataset, the automatic approach on average takes less than five minutes to complete, and gives more consistent results across datasets.

Angiography is an invasive procedure since contrast medium is injected into circulatory system of patients and the mostly preferred technique is X-ray angiography. For diagnosis, treatment planning, and risk assessment purposes, interventional radiologists utilize visual inspection to determine connectivity relations between vessels. This situation leads angiography to be more invasive, since it requires additional injection of contrast medium and X-ray dose. This thesis work presents a 3-D vascular connectivity tracking toolkit for automated extraction of vascular networks in 3-D medical images. The proposed method automatically extracts the vascular network connected to a user-defined point in a user-defined direction, and requires no further user interaction. The toolkit prevents additional injection of contrast agent and X-ray dose, saves time for the interventional radiologist. While the algorithm is applicable on all 3-D angiography images, performance of the method is observed on 3-D catheter angiography image of cerebrovascular structures. The algorithm iteratively tracks gravity centers of vascular branches in the user-defined direction, preserving connection to the user-defined point. Curvy branches are tracked even if they have discontinuous portions. Since this tracking method does not depend on lumen diameter and intensity differences, branches with stenoses and branches having large intensity difference can be successfully tracked. Skeletonization and junction detection methods are described, which are used to detect the sub branches, indirectly connected to the point. These methods are capable of handling bifurcations, trifurcations, and junctions having more branches. However, false junctions occurring due to superposition of vessels are not eliminated.

The application of preoperative magnetic resonance angiography in the treatment of critical leg ischemia in patients with diabetes ABBREVIATIONS ABPI -ankle brachial pressure index AI - ankle index ARO - arterial runoff CLI - critical limb ischemia DM – diabetes mellitus DSA- digital subtraction angiography DU - duplex ultrasonography GSV- great saphenous vein HKUM - Hospital of Kaunas University of Medicine IHD - ischemic heart disease IS - ischaemic stroke MRA - magnetic resonance angiography NAV – not reversed autovein PAOD - peripheral artery disease PATE - pulmonary artery tromboembolia SD - standard deviation χ2 - Chi-square 1. INTRODUCTION Complications of atherosclerosis and diabetes mellitus rank among the greatest “scourges” of the aging population. In the majority of developed countries, mortality from complications of atherosclerosis occupies the 1st – the 2nd places, and mortality from complications of DM – the 3rd – the 4th places [Šulcaitė R., 2002]. One of the main risk factors for the development of atherosclerosis is diabetes mellitus (DM)[Eskelinen, E., 2003; Kozek, E., 2003; Yokoyama, H., 2003]. Clinical manifestations of atherosclerosis are ischemic heart disease (IHD), cerebral ischemia (CI), and obliterative atherosclerosis, or peripheral artery occlusive disease (PAOD). At present, diabetologists used the term diabetes lipidus, thus combining these two diseases into one. Up to 70% of amputations of non-traumatic origin... [to full text]

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