Non contrast-enhanced MRA versus ultrasound blood vessel assessment to determine the choice of hemodialysis vascular access

Purpose: The aim of this work was to establish the relationship between traditional blood vessel mapping for vascular access (VA) creation by B-mode ultrasound (US) and novel non contrast-enhanced magnetic resonance angiography ¿(NCE-MRA), and to study the potential influence of the diameter assessment technique on the choice of hemodialysis vascular access.Methods: A total of 27 end-stage renal-disease patients were included. They received routine US and a NCE-MRA examination of the upper extremity. Diameters were measured manually on US and semi-automatically on NCE-MRA. These measurements were statistically compared for the arteries and veins and for each measurement location. Furthermore, sensitivity and specificity of both modalities to predict VA location was investigated by comparison with an experienced surgeon. This analysis gave insight into the potential influence of vessel mapping modality on decision-making.Results: Comparison of NCE-MRA with US for the arteries and veins, demonstrated a bias of 9% (limits -33%-78%) and 38% (limits -36%-198%), respectively. Statistically significant differences between the modalities on the individual locations were mainly found for the venous locations. The sensitivity and specificity for US to predict VA location was 1.0 and 0.74, respectively, while for NCE-MRA this was 0.88 and 0.39, respectively.Conclusions: The results obtained indicate that extreme caution should be exercised when replacing one diameter measurement modality with the other. A further need exists to improve both vessel mapping protocols to obtain a geometric description of the upper extremity vasculature regardless of acquisition modality. End I

Importance of initial stress for abdominal aortic aneurysm wall motion: Dynamic MRI validated finite element analysis

Currently the transverse diameter is the primary decision criterion to assess rupture risk in patients with an abdominal aortic aneurysm (AAA). To obtain a measure for more patient-specific risk assessment, aneurysm wall stress, calculated using finite element analysis (FEA), has been evaluated in literature. In many cases, initial stress, present in the AAA wall during image acquisition, is not taken into account. In the current study the effect of initial stress incorporation (ISI) is determined by directly comparing wall displacements extracted from FEA and dynamic MRI. Ten patients with an aneurysm diameter > 5.5 cm were scanned with cardiac triggered MRI. Semi-automatic segmentation of the AAA was performed on the diastolic phase. The segmented in-slice contours were propagated through the remaining cardiac phases using an active contour model as to track wall displacements on MRI. Consequently, FEA with and without ISI (no-ISI) was performed using the diastolic geometry with simultaneously measured intra-aneurysm pressure values as boundary condition. Contours extracted from FEA were compared with MRI contours at corresponding cardiac phases by distance and relative area differences. The wall displacements from FEA with ISI show significant better correspondence with wall motion from MRI data in comparison with the no-ISI FEA (deviation in wall displacement 1.7% vs. 12.4%; p <0.001). Based on these results it can be concluded that incorporation of initial stress significantly improves wall displacement accuracy of FEA and therefore it should be incorporated in future analyses. © 2009 Elsevier Ltd. All rights reserved

Feasibility of non-contrast-enhanced magnetic resonance angiography for imaging upper extremity vasculature prior to vascular access creation.

Item does not contain fulltextOBJECTIVES: Preoperative mapping of arterial and venous anatomy helps to prevent postoperative complications after vascular access creation. The use of gadolinium in contrast-enhanced (CE) magnetic resonance angiography (MRA) has been linked to nephrogenic systemic fibrosis in patients with end-stage renal disease (ESRD). The purpose of this study was to evaluate non-contrast-enhanced (NCE) MRA for assessment of upper extremity and central vasculature and to compare it with CE-MRA. METHODS: NCE and CE-MRA images were acquired in 10 healthy volunteers and 15 patients with ESRD. In each data set, two observers analysed 11 arterial and 16 venous segments with regard to image quality (0-4), presence of artefacts (0-2) and vessel-to-background ratio. RESULTS: More arterial segments were depicted using CE-MRA compared to NCE-MRA (99% vs. 96%, p = 0.001) with mean image quality of 3.80 vs. 2.68, (p < 0.001) and mean vessel-to-background ratio of 6.47 vs. 4.14 (p < 0.001). Ninety-one percent of the venous segments were portrayed using NCE-MRA vs. 80% using CE-MRA (p < 0.001). Mean image quality and vessel-to-background ratio were 2.41 vs. 2.21 (p = 0.140) and 5.13 vs. 3.88 (p < 0.001), respectively. CONCLUSIONS: Although arterial image quality and vessel-to-background ratios were lower, NCE-MRA is considered a feasible alternative to CE-MRA in patients with ESRD who need imaging of the upper extremity and central vasculature prior to dialysis access creation.1 januari 201