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This study hypothesized that arterial spin labeling (ASL) magnetic resonance (MR) imaging at 3-T would be a reliable noncontrast technique for measuring peak exercise calf muscle blood flow in both healthy volunteers and patients with peripheral arterial disease (PAD) and will discriminate between these groups.Prior work demonstrated the utility of first-pass gadolinium-enhanced calf muscle perfusion MR imaging in patients with PAD. However, patients with PAD often have advanced renal disease and cannot receive gadolinium.PAD patients had claudication and an ankle brachial index of 0.4 to 0.9. Age-matched normal subjects (NL) had no PAD risk factors and were symptom-free with exercise. All performed supine plantar flexion exercise in a 3-T MR imaging scanner using a pedal ergometer until exhaustion or limiting symptoms and were imaged at peak exercise with 15 averaged ASL images. Peak perfusion was measured from ASL blood flow images by placing a region of interest in the calf muscle region with the greatest signal intensity. Perfusion was compared between PAD patients and NL and repeat testing was performed in 12 subjects (5 NL, 7 PAD) for assessment of reproducibility.Peak exercise calf perfusion of 15 NL (age: 54 ± 9 years) was higher than in 15 PAD patients (age: 64 ± 5 years, ankle brachial index: 0.70 ± 0.14) (80 ± 23 ml/min - 100 g vs. 49 ± 16 ml/min/100 g, p0.001). Five NL performed exercise matched to PAD patients and again demonstrated higher perfusion (84 ± 25 ml/min - 100 g, p0.002). As a measure of reproducibility, intraclass correlation coefficient between repeated studies was 0.87 (95% confidence interval [CI]: 0.61 to 0.96). Interobserver reproducibility was 0.96 (95% CI: 0.84 to 0.99).ASL is a reproducible noncontrast technique for quantifying peak exercise blood flow in calf muscle. Independent of exercise time, ASL discriminates between NL and PAD patients. This technique may prove useful for clinical trials of therapies for improving muscle perfusion, especially in patients unable to receive gadolinium.

ObjectivesThe purpose of this paper was to compare quantitative cardiac magnetic resonance (CMR) first-pass contrast-enhanced perfusion imaging to qualitative interpretation for determining the presence and severity of coronary artery disease (CAD).BackgroundAdenosine CMR can detect CAD by measuring perfusion reserve (PR) or by qualitative interpretation (QI).MethodsForty-one patients with an abnormal nuclear stress scheduled for X-ray angiography underwent dual-bolus adenosine CMR. Segmental myocardial perfusion analyzed using both QI and PR by Fermi function deconvolution was compared to quantitative coronary angiography.ResultsIn the 30 patients with complete quantitative data, PR (mean ± SD) decreased stepwise as coronary artery stenosis (CAS) severity increased: 2.42 ± 0.94 for 70% (p < 0.001). The PR and QI had similar diagnostic accuracies for detection of CAS >50% (83% vs. 80%), and CAS >70% (77% vs. 67%). Agreement between observers was higher for quantitative analysis than for qualitative analysis. Using PR, patients with triple-vessel CAD had a higher burden of detectable ischemia than patients with single-vessel CAD (60% vs. 25%; p = 0.02), whereas no difference was detected by QI (31% vs. 21%; p = 0.26). In segments with myocardial scar (n = 64), PR was 3.10 ± 1.34 for patients with CAS 50% (p < 0.0001).ConclusionsQuantitative PR by CMR differentiates moderate from severe stenoses in patients with known or suspected CAD. The PR analysis differentiates triple- from single-vessel CAD, whereas QI does not, and determines the severity of CAS subtending myocardial scar. This has important implications for assessment of prognosis and therapeutic decision making.

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ObjectivesWe aimed to investigate the pathophysiology of peripheral arterial disease (PAD) by examining magnetic resonance imaging (MRI) and spectroscopic (MRS) correlates of functional capacity.BackgroundDespite the high prevalence, morbidity, and cost of PAD, its pathophysiology is incompletely understood.MethodsEighty-five patients (age 68 ± 10 years) with mild-to-moderate PAD (ankle-brachial index 0.69 ± 0.14) had their most symptomatic leg studied by MRI/MRS. Percent wall volume in the superficial femoral artery was measured with black blood MRI. First-pass contrast-enhanced MRI calf muscle perfusion and 31P MRS phosphocreatine recovery time constant (PCr) were measured at peak exercise in calf muscle. All patients underwent magnetic resonance angiography (MRA), treadmill testing with maximal oxygen consumption measurement, and a 6-min walk test.ResultsMean MRA index of number and severity of stenoses was 0.84 ± 0.68 (normal 0), % wall volume 74 ± 11% (normal 46 ± 7%), tissue perfusion 0.039 ± 0.015 s−1(normal 0.065 ± 0.013 s−1), and PCr 87 ± 54 s (normal 34 ± 16 s). MRA index, % wall volume, and ankle-brachial index correlated with most functional measures. PCr was the best correlate of treadmill exercise time, whereas calf muscle perfusion was the best correlate of 6-min walk distance. No correlation was noted between PCr and tissue perfusion.ConclusionsFunctional limitations in PAD are multifactorial. As measured by MRI and spectroscopy, atherosclerotic plaque burden, stenosis severity, tissue perfusion, and energetics all play a role. However, cellular metabolism is uncoupled from tissue perfusion. These findings suggest a potential role for therapies that regress plaque, increase tissue perfusion, and/or improve cellular metabolism. (Comprehensive Magnetic Resonance of Peripheral Arterial Disease; NCT00587678)