Medicine (Austin & Northern Health) - Research Publications
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ItemComprehensive arterial assessment in diabetic patients using combined quiescent interval single shot (QISS) imaging for leg imaging and QISS-arterial spin labeled MRA for pedal imaging: preliminary experience with comparison to DSA(International Society for Magnetic Resonance in Medicine, 2014)Target Audience Clinicians and basic scientists with an interest in non-invasive imaging of peripheral arterial disease. Purpose Imaging diabetic patients with peripheral arterial disease (PAD) is critical for revascularization planning. PAD in diabetic patients is commonly distal, and imaging of the pedal arteries is desirable to identify potential bypass targets. Concomitant renal impairment may contribute to difficulties with conventional imaging. Quiescent interval single shot (QISS) MRA is a recently described non-contrast enhanced technique with high reported accuracy. However, it is challenging to perform in the feet, due to inhomogeneous shim and slow arterial flow, with QISS with arterial spin labeling (QISS-ASL) described to improve pedal artery visualization. The purpose of this study was to evaluate feasibility and accuracy of a combined QISS/QISS-ASL approach (cQISS-MRA) for evaluating diabetic patients with symptomatic PAD, using DSA as the reference standard. Methods 15 diabetic patients (7M, 8F, mean 72y, range 42-91y, eGFR 7-91 ml/min/1.73m2) with symptomatic PAD were prospectively recruited for cQISS-MRA at 1.5T (Siemens, Avanto) 0-36 days prior to clinically required DSA. Initially, pedal QISS-ASL MRA was performed with a 12-channel head coil. Subsequently, QISS MRA of infrarenal aorta to feet was performed with peripheral, body and spine array coils. Common parameters for QISS MRA and QISS-ASL MRA were: FA 90°, in plane resolution 1 x 1mm2, BW 658 Hz/Px, acceleration factor 2 (GRAPPA). For QISS MRA: TR/TE 3.5/1.4ms, sl 3mm (additional 1.2mm imaging through calf), FOV 400 x 260, 9 stations, 48 sl, total acquisition 432 RR intervals, quiescent interval 350ms. For QISS-ASL: TR/TE 3.7/1.6ms, quiescent interval 228ms, FOV 400 x 240, sl 1.2mm, 2 stations, 128 sl, total acquisition 256 RR intervals. DSA was performed with iodinated contrast (n=14) or carbon dioxide (CO2, n=1) with coverage determined by clinical indication. MRA and DSA images were anonymized and evaluated by a cardiovascular and vascular/interventional radiologist respectively on a PACS workstation (Impax, Agfa). Diagnostic confidence (1=non- diagnostic, 3=diagnostic, 5=highly confident) was recorded and compared with the Wilcoxon signed rank test. MRA diagnostic confidence was compared between regions (pelvis, thigh, calf and foot) with the Mann-Whitney U test. Segmental stenosis was graded in up to 39 segments per patient. cQISS- MRA sensitivity and specificity for hemodynamically significant (≥50%) stenosis was calculated against DSA for all available segments. Results Imaging was completed in 13/15 patients with 2 incomplete studies (BMI 40 precluding imaging of pelvis and thigh, n=1; patient discomfort, n=1). DSA correlation (Fig 1) was available in 19 legs in 15 patients, with pelvic DSA only in 1 patient. For all segments where DSA was available, cQISS-MRA mean diagnostic confidence was 4.00±0.96, significantly higher than DSA 3.72±0.84, p<0.0001, with 12 non-diagnostic (score of 1) DSA segments at CO2 angiography, and 5 non-diagnostic MRA segments (susceptibility from joint prostheses). For cQISS-MRA, there was significantly lower diagnostic confidence in the foot compared with other regions (pelvis 3.87±0.93, thigh 4.0±1.0, calf 4.2±0.77, foot 2.41±1.1, p<0.0001 for all regions compared to the foot). Factors negatively impacting MRA diagnostic confidence and accuracy were: for QISS- MRA, step artifact from motion/ mistriggering and inhomogeneous fat suppression; for QISS-ASL MRA, motion artifact and image noise. Excluding non-diagnostic DSA and MRA segments, 309 segments were assessed for stenosis, with 142 (46.0%) demonstrating hemodynamically significant stenosis. Overall, there was 74.7% sensitivity and 86.8% specificity for cQISS-MRA, highest for aortoiliac segments, and lowest for pedal segments (Table 1). Discussion/ Conclusion A combined QISS MRA and QISS-ASL MRA approach is feasible for infrarenal aorta to pedal arterial assessment in diabetic patients with symptomatic PAD. There is good diagnostic confidence for pelvic to calf imaging and lower diagnostic confidence for pedal imaging. Accuracy of the technique is higher for proximal stations, with susceptibility artifact and inhomogeneous fat suppression impacting stenosis assessment. Pedal imaging is degraded by motion and relatively low SNR, however still enables identification of potential distal bypass targets in a patient population with a substantial burden of disease. This includes patients with end stage renal failure, where even DSA may be challenging. Assessment of potential clinical utility of cQISS-MRA for guiding management is planned. Further refinements to accelerate QISS-ASL MRA, and strategies to improve robustness to motion, including non-Cartesian acquisition, could improve test accuracy for pedal arterial stenosis.
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ItemEndovascular repair of ruptured AAA: barriers to uptake in Australian and New Zealand centres(ANZ Journal of Surgery, 2014)
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ItemMulti detector (64+) CT angiography of the lower limb in symptomatic peripheral arterial disease - preliminary assessment of accuracy and inter-observer agreement in an Australian tertiary care setting(Royal Australian and New Zealand College of Radiologists, 2014)Multidetector computed tomography angiography (CTA) is a reliable, widely available technology now commonly used in the initial evaluation of peripheral arterial disease (PAD). Meta-analyses comparing mainly 2-, 4-, and 16-detector multidetector CTA with the gold standard, digital subtraction angiography (DSA), have shown it to be highly accurate in patients with symptomatic lower extremity PAD [1,2]. CTA has a number of advantages over DSA including minimal invasiveness, shorter examination times, smaller volumes of contrast material used and a lower rate of complications. However, limitations of CTA include its susceptibility to 'blooming artifacts' when vessel wall calcifications are present, and potentially decreased accuracy in detecting and quantifying in-stent restenosis due to metallic or beam hardening artefact [3,4]. The purpose of this study was to evaluate the accuracy and inter-observer agreement of current generation (64+ detector) multidetector CTA for detection of haemodynamically significant stenosis in patients with symptomatic PAD in a tertiary care setting using digital subtraction angiography DSA as the reference standard.