J.B.TowneL.H.HollierComplications in Vascular Surgery(2nd Edition)2004Marcel Dekker Inc.New York272pp., $165

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Intravascular Ultrasound and Peripheral Endovascular Interventions

In recent years the interest in minimal invasive surgery has been growing and the same trend can be observed in vascular surgery, leading to what is commonly referred to as lIendovascular surgery". Although the 1990s represent an era of technical revolution in vascular surgery, it is a misunderstanding to consider endovascular treatment a recent development. In 1947 J050 Cid dos Santos described the thrombo-endarterectomy'; this technique was modified by Vollmar in 1964, to a semi-closed endarterectomy using ringstrippers'> In the same year other pioneers, including Dotter and Judkins, published prelinlinary results on what they called "angioplasty" of the femoropopliteal artery using coaxial eatheters.3 This technique was later modified by Griintzig in 1974, who replaced the coaxial catheters with dilatation balloons.' In the early 1990s, Volodos and Parodi introduced the endovascular treatment of the abdominal aortic aneurysm with a device composed of a Dacron graft and Palmaz stents.5 ,6 The collaboration between interventional radiologists and vascular surgeons has been of eminent importance for further evolution of endovascular teclmiques. Nowadays a great variety of obstmctive and aneurysmal peripheral vascular diseases can be treated with catheter-guided, endovascular and, therefore, less invasive techniques. The development of these endovascular techniques prompted the need for improved vascular imaging and better diagnostics. Since angiography displays only a "lumenogram II of the vessel, tills prechldes qualitative evaluation of atherosclerotic plaque and quantitative assessment of plaque and vessel. Sophisticated modalities such as colour duplex, computed tomographic angiography and magnetic resonance imaging can be important in the pre- and postintervention assessment of vascular disease. These techniques, however, do not always give accurate information on the dimensions of the vessel or the extent of the disease and at the present time cannot be used during intervention.7 Intravascular ultrasound depicts both the vascular lumen and vascular wall: thus, inform

Visualizing the 3D collagen structure of human atherosclerotic plaques using Diffusion Tensor Imaging

Introduction Ischemic strokes and heart attacks are mainly caused by rupture of the fibrous cap of an atherosclerotic plaque. Reliable prediction of the fibrous cap rupture is, therefore, crucial to prevent these potentially lethal cardiovascular events. Since cap rupture occurs when the stresses in the cap exceed the strength of the cap, biomechanical modeling may help to improve cap rupture prediction. Biomechanical models depend strongly on the material parameters used as input. Previous studies focused on the anisotropic mechanical behaviour of atherosclerotic plaques and produced stiffness values for the collagen fibers in plaques [1]. However, for a more complete characterization knowledge of the global 3D collagen architecture in atherosclerotic plaques is required. Therefore, for the first time diffusion tensor imaging (DTI) was used to investigate the 3D collagen structure of human atherosclerotic plaques. Methods Until now five human carotid atherosclerotic plaques were obtained from endarterectomy patients and embedded in 4 % type VII agarose. The samples were placed in a 9.4 T horizontal-bore MRI scanner to conduct DTI. DTI enabled the tracking of the fiber directions and visualisation of the collagen fibers [2]. Results The consistent results of five different plaques suggest that collagen fibers are deposited in a new layer in a different direction during the development of atherosclerosis (see figure for one representative result). Two distinct layers of collagen fibers were found; an outer layer, where the collagen is aligned in the circumferential direction (14.5°±28.0°), similar to healthy arteries [2], and an inner layer where the collagen follows a longitudinal direction (77.4°±22.4°). Conclusions DTI allowed the visualization of the global 3D collagen architecture of atherosclerotic plaques. The inner collagen layer showed a surprising result and implies a change of strain distribution in the artery during the later stage of atherosclerosis, possibly due to the thickening and stiffening of the diseased intimal tissue. These data, combined with collagen stiffness data found in previous studies [1], will be used as input for biomechanical models including the anisotropic mechanical behaviour of plaque tissue. Models using general over-simplified assumptions like isotropic behaviour can be replaced by models including the anisotopic behavior and thereby improve the stress analysis of plaques. Improved models might help in the diagnosis and treatment of plaque rupture preventing heart attacks and ischemic strokes. References [1] Chai C-K, Akyildiz AC, Speelman L, Gijsen FJH, Oomens CWJ, Sambeek MRHM, van der Lugt A, Baaijens FTP, Anisotropic mechanical behaviour of carotid atherosclerotic plaques at large strain, The 8th international symposium on Biomechanics in Vascular Biology and Cardiovascular Disease, Rotterdam, 2013. [2] Ghazanfari S, Driessen-Mol A, Strijkers GJ, Kanters FMW, Baaijens FPT, Bouten CVC, A comparative analysis of the collagen architecture in the carotid artery: Second harmonic generation versus diffusion tensor imaging, Biochemical and Biophysical Research Communications, 426(1): 54-58, 2012

Evaluation of a dedicated dual phased-array surface coil using a black-blood FSE sequence for high resolution MRI of the carotid vessel wall

Purpose: To investigate the ability of magnetic resonance imaging (MRI) to visualize the carotid vessel wall using a phased-array coil and a black-blood (BB) fast spin-echo (FSE) sequence. Materials and Methods: The phased-array coil was compared with a three-inch coil. Images from volunteers were evaluated for artifacts, wall layers, and wall signal intensity. Signal intensity and homogeneity of atherosclerosis were assessed. Lumen diameter and vessel area were measured. Results: Comparison between the phased-array coil and the three-inch coil showed a 100% increase in signal-to-noise ratio. BB-FSE imaging resulted in good delineation between blood and vessel wall. Most volunteers had a two-layered vessel wall with a hyperintense inner layer. MRI showed both homogeneous hyperintense and heterogeneous plaques, which consisted of a main hyperintense part with hypointense spots and/or intermediate regions. MRI lumen and area measurements were performed easily. Conclusion: High resolution MRI of carotid atherosclerosis is feasible with a phased-array coil and a BB-FSE sequence