Percutaneous intervention in peripheral artery disease improves calf muscle phosphocreatine recovery kinetics: a pilot study.

We hypothesized that percutaneous intervention in the affected lower extremity artery would improve calf muscle perfusion and cellular metabolism in patients with claudication and peripheral artery disease (PAD) as measured by magnetic resonance imaging (MRI) and spectroscopy (MRS). Ten patients with symptomatic PAD (mean ± SD: age 57 ± 9 years; ankle-brachial index (ABI) 0.62 ± 0.17; seven males) were studied 2 months before and 10 months after lower extremity percutaneous intervention. Calf muscle phosphocreatine recovery time constant (PCr) in the revascularized leg was measured by (31)P MRS immediately after symptom-limited exercise on a 1.5-T scanner. Calf muscle perfusion was measured using first-pass gadolinium-enhanced MRI at peak exercise. A 6-minute walk and treadmill test were performed. The PCr recovery time constant improved significantly following intervention (91 ± 33 s to 52 ± 34 s, p < 0.003). Rest ABI also improved (0.62 ± 0.17 to 0.93 ± 0.25, p < 0.003). There was no difference in MRI-measured tissue perfusion or exercise parameters, although the study was underpowered for these endpoints. In conclusion, in this pilot study, successful large vessel percutaneous intervention in patients with symptomatic claudication, results in improved ABI and calf muscle phosphocreatine recovery kinetics.

Low-density lipoprotein lowering does not improve calf muscle perfusion, energetics, or exercise performance in peripheral arterial disease.

OBJECTIVES: We hypothesized that low-density lipoprotein (LDL) reduction regardless of mechanism would improve calf muscle perfusion, energetics, or walking performance in peripheral arterial disease (PAD) as measured by magnetic resonance imaging and magnetic resonance spectroscopy. BACKGROUND: Statins improve cardiovascular outcome in PAD, and some studies suggest improved walking performance. METHODS: Sixty-eight patients with mild to moderate symptomatic PAD (age 65 ± 11 years; ankle-brachial index [ABI] 0.69 ± 0.14) were studied at baseline and annually for 2 years after beginning simvastatin 40 mg (n = 20) or simvastatin 40 mg/ezetimibe 10 mg (n = 18) if statin naïve, or ezetimibe 10 mg (n = 30) if taking a statin. Phosphocreatine recovery time was measured by (31)P magnetic resonance spectroscopy immediately after symptom-limited calf exercise on a 1.5-T scanner. Calf perfusion was measured using first-pass contrast-enhanced magnetic resonance imaging with 0.1 mM/kg gadolinium at peak exercise. Gadolinium-enhanced magnetic resonance angiography was graded. A 6-min walk and a standardized graded Skinner-Gardner exercise treadmill test with peak Vo(2) were performed. A repeated-measures model compared changes over time. RESULTS: LDL reduction from baseline to year 2 was greater in the simvastatin 40 mg/ezetimibe 10 mg group (116 ± 42 mg/dl to 56 ± 21 mg/dl) than in the simvastatin 40 mg group (129 ± 40 mg/dl to 90 ± 30 mg/dl, p < 0.01). LDL also decreased in the ezetimibe 10 mg group (102 ± 28 mg/dl to 79 ± 27 mg/dl, p < 0.01). Despite this, there was no difference in perfusion, metabolism, or exercise parameters between groups or over time. Resting ABI did improve over time in the ezetimibe 10 mg group and the entire study group of patients. CONCLUSIONS: Despite effective LDL reduction in PAD, neither tissue perfusion, metabolism, nor exercise parameters improved, although rest ABI did. Thus, LDL lowering does not improve calf muscle physiology or functional capacity in PAD. (Comprehensive Magnetic Resonance of Peripheral Arterial Disease; NCT00587678).

The effect of ezetimibe on peripheral arterial atherosclerosis depends upon statin use at baseline.

BACKGROUND: Both statins and ezetimibe lower LDL-C, but ezetimibe's effect on atherosclerosis is controversial. We hypothesized that lowering LDL-C cholesterol by adding ezetimibe to statin therapy would regress atherosclerosis measured by magnetic resonance imaging (MRI) in the superficial femoral artery (SFA) in peripheral arterial disease (PAD). METHODS: Atherosclerotic plaque volume was measured in the proximal 15-20 cm of the SFA in 67 PAD patients (age 63 ± 10, ABI 0.69 ± 0.14) at baseline and annually × 2. Statin-naïve patients (n=34) were randomized to simvastatin 40 mg (S, n=16) or simvastatin 40 mg+ezetimibe 10mg (S+E, n=18). Patients already on statins but with LDL-C >80 mg/dl had open-label ezetimibe 10mg added (E, n=33). Repeated measures models estimated changes in plaque parameters over time and between-group differences. RESULTS: LDL-C was lower at year 1 in S+E (67 ± 7 mg/dl) than S (91 ± 8 mg/dl, p<0.05), but similar at year 2 (68 ± 10 mg/dl vs. 83 ± 11 mg/dl, respectively). Plaque volume did not change from baseline to year 2 in either S+E (11.5 ± 1.4-10.5 ± 1.3 cm(3), p=NS) or S (11.0 ± 1.5-10.5 ± 1.4 cm(3), p=NS). In E, plaque progressed from baseline to year 2 (10.0 ± 0.8-10.8 ± 0.9, p<0.01) despite a 22% decrease in LDL-C. CONCLUSIONS: Statin initiation with or without ezetimibe in statin-naïve patients halts progression of peripheral atherosclerosis. When ezetimibe is added to patients previously on statins, peripheral atherosclerosis progressed. Thus, ezetimibe's effect on peripheral atherosclerosis may depend upon relative timing of statin therapy.

Vascular surgery career resource.

Vascular surgery has undergone a minimally invasive revolution in the past 15 years. The subspecialty emerged with many changes to its training paradigms that have made this field more attractive to both medical student and general surgery resident candidates. Commitment to diagnosis and treatment of arterial, venous, and lymphatic systems disorders remains the cornerstone of this profession, but an entirely new generation of endovascular treatments has been added to the staple of open surgical procedures used to treat these diseases. A wide variety of practice options are available, ranging from high-stress, technologically demanding complex arterial repairs to low-risk, outpatient, venous insufficiency treatment and all combinations in-between. Many online resources are available to allow an interested candidate to stay current with all the exciting changes in the field. This information is maintained by strong national organizations of vascular surgeons.

Metachronous bilateral posterior tibial artery aneurysms in Ehlers-Danlos syndrome type IV.

Ehlers-Danlos syndrome type IV is a life-threatening genetic connective tissue disorder. We report a 24-year-old woman with EDS-IV who presented with metachronous bilateral aneurysms/pseudoaneurysms of the posterior tibial arteries 15 months apart. Both were treated successfully with transarterial coil embolization from a distal posterior tibial approach.

The incidence of pulmonary neoplasms discovered by serial computed tomography scanning after endovascular abdominal aortic aneurysm repair.

OBJECTIVES: Serial computed tomography (CT) scanning is routinely used to follow up endovascular exclusion of abdominal aortic aneurysms (AAAs). Nonvascular diseases can be identified, and these exams include images of the lung bases, which can provide information that leads to the diagnosis of pulmonary neoplasms. This study was conducted to determine the rate and type of pulmonary-based oncologic diseases identified by serial CT scanning of patients with endovascular repair of AAAs. METHODS: A retrospective review of 138 consecutive patients receiving endovascular AAA exclusion during an 8-year period was performed. Length of follow-up and number of CT scans performed was recorded. CT characteristics of the lesion (size, character, and suspicion of malignancy), type of biopsy procedure performed, and final pathologic diagnosis were collected. Oncologic treatments and survival length were also evaluated. RESULTS: Pulmonary lesions were found in 25 patients (18%), of whom 5 (4%) died during follow-up, and 13 (9%) had stable, subcentimeter lesions and continue to have surveillance from vascular specialists only. Seven patients (5%) with pulmonary lesions were referred for evaluation by thoracic surgeons. Six patients (4%) underwent biopsy of the lesion and were diagnosed with cancer. One patient refused a biopsy and is being monitored with serial CT scans. Four lung cancers (1 small cell and 3 non-small cell), one primary pulmonary carcinoid tumor, and one B-cell lymphoma were discovered. No changes were noted in the lesions in the patient receiving CT surveillance. More than half of the cancers were diagnosed in stage I, with a mean lesion diameter of 11 mm at biopsy. Of 25 patients with pulmonary nodules, 24 were men. The patients diagnosed with cancer are all still alive, with a mean survival length of 2.5 years (range, 0.5-6 years) after oncologic treatment. CONCLUSIONS: Serial CT scans may reveal a high rate of pulmonary malignancies in a population with AAAs. Attention to the incidental finding of pulmonary nodules on CT scans and arrangement of appropriate follow-up by the vascular surgeon is important for patients undergoing surveillance after endovascular AAA repair. These results indicate that aggressive management of these lesions (early thoracic surgery consultation and biopsy) is appropriate in this high-risk population and may offer early diagnosis and improved long-term survival.

The plasma microparticle proteome.

All cell types shed ectosomes and exosomes, collectively known as microparticles (MP; 0.1 to 1.5 µm in diameter), when activated or stressed; normal human plasma contains ~2 µg MP protein/mL. The cellular composition of plasma MP is altered in many diseases, including acute coronary syndrome, diabetes mellitus, sepsis, and sickle cell disease. We measured the plasma MP protein composition of 42 patients (median age 69.5 years, most with cardiovascular disease) by label-free liquid chromatography coupled to tandem mass spectrometry. Among 458 proteins detected with high confidence (identified by at least two unique peptides with SEQUEST XCor (Thermo Electron Corp., San Jose, CA) ≥ 2.0, 2.2, and 3.3 for charge states +1, +2, and +3, respectively), 130 were present in most patients, representing a "core" set of plasma MP proteins. This core is enriched in cytoskeletal, integrin complex, and hemostasis proteins, and spectral counts of several proteins correlate with patient age and gender. We conclude that the MP proteome may be a useful and reliable source of biologically relevant disease biomarkers.

Outcomes of covered kissing stent placement compared with bare metal stent placement in the treatment of atherosclerotic occlusive disease at the aortic bifurcation.

PURPOSE: To review the outcomes with the use of balloon-expandable covered iliac kissing stents as compared with bare metal stents in the treatment of atherosclerotic disease at the aortic bifurcation. MATERIALS AND METHODS: A review of consecutive patients from a single institution with atherosclerotic occlusive disease at the aortic bifurcation treated with balloon-expandable kissing stents was performed between January 1, 2002, and September 1, 2007. Fifty-four patients were identified and divided into two groups: those with bare metal stents and those with covered stents. Technical and clinical success (Fontaine classification), complications, and patency at follow-up were documented. RESULTS: Twenty-six patients (17 men, nine women; mean age, 61 years; age range, 39-79 years) received covered stents and 28 patients (15 men, 13 women; mean age, 61 years; age range, 38-82 years) received bare metal stents. Technical success was achieved in 100% of patients in both groups. Major complications occurred in three of the 26 (11%) with covered stents (P = .66) and two of the 28 patients (7%) with bare metal stents. The median follow-up was 21 months (20 months for covered stents vs 25 months for bare metal stents; range, 1-62 months). Twenty-two of the 26 patients (85%) with covered stents had sustained improvement in clinical symptoms during the follow-up period compared with 15 of the 28 patients (54%) with bare metal stents (P = .02). Primary patency rates at 1 and 2 years were 92% and 92%, respectively, for covered stents and 78% and 62% for bare metal stents (P = .023). CONCLUSIONS: The use of covered balloon-expandable kissing stents for atherosclerotic aortic bifurcation occlusive disease provides superior patency at 2 years as compared with bare metal balloon-expandable stents.

Transplant pneumonectomy in a patient with an acutely thrombosed allograft.

Transplant pneumonectomy is most commonly performed in the setting of retransplantation and is rare for other indications. We present a case of an elderly woman who is 3 years postoperative left, single lung transplantation with a history of emphysema that developed extensive infarction of her transplanted lung secondary to thromboembolic disease. She required an allograft pneumonectomy as treatment for this and was eventually discharged on bi-level nasal positive pressure at night and 3 L nasal cannula oxygen during the day.

Atrial fibrillation is associated with increased risk of perioperative stroke and death from carotid endarterectomy.

BACKGROUND: Carotid endarterectomy is performed in high volume in the United States. Identifying patients with a higher risk of stroke and death after carotid endarterectomy can lead to modifications in care that would significantly reduce the occurrence of these events. This study evaluates whether atrial fibrillation is significantly associated with an increased risk of death or stroke for patients undergoing carotid endarterectomy. METHODS: This retrospective cohort study uses multivariable logistic regression analysis to assess the relationship between atrial fibrillation and death and/or stroke after carotid endarterectomy. The study population is drawn from the National Inpatient Sample, 2005. All patients with a primary carotid endarterectomy and diagnosis of stenosis of precerebral arteries were included, except patients with concomitant open heart procedures. The main outcomes examined were in-hospital death and stroke, adjusted for age, gender, symptomatic status, and for comorbid disease. RESULTS: Carotid endarterectomy was performed for 20,022 patients. Strokes occurred in 189 patients (0.94%), and death occurred in 59 (0.29%). Patients with atrial fibrillation had significantly higher adjusted odds of stroke or death (odds ratio = 2.45; P < .0001). CONCLUSION: Patients with atrial fibrillation have a substantially higher risk of stroke and death after carotid endarterectomy.

Multifactorial determinants of functional capacity in peripheral arterial disease: uncoupling of calf muscle perfusion and metabolism.

OBJECTIVES: We aimed to investigate the pathophysiology of peripheral arterial disease (PAD) by examining magnetic resonance imaging (MRI) and spectroscopic (MRS) correlates of functional capacity. BACKGROUND: Despite the high prevalence, morbidity, and cost of PAD, its pathophysiology is incompletely understood. METHODS: Eighty-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 (31)P 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. RESULTS: Mean 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. CONCLUSIONS: Functional 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).

Unusual anomaly complicating abdominal aortic aneurysm repair: anterior inferior vena cava.

This case illustrates an unusual anomaly of the great veins. To our knowledge, these are the first published photographs of the vena cava traversing anterior to the distal aorta. This anatomic variant caused minor technical problems during open abdominal aortic aneurysm repair.

Outback catheter-assisted simultaneous antegrade and retrograde access for subintimal recanalization of peripheral arterial occlusion.

Subintimal recanalization techniques have been shown to be beneficial in selected patients with severe peripheral vascular disease with tissue loss or rest pain and limited surgical options. In this report, we use an Outback catheter in order to gain access to the subintimal channel from the true lumen during percutaneous intentional extraluminal recanalization using the subintimal arterial flossing with antegrade-retrograde intervention (SAFARI) technique. To the best of our knowledge, this is the first report where the Outback catheter was used in antegrade fashion in order to gain access to the subintimal space from the true lumen using the SAFARI technique.

Current issues in the treatment of women with abdominal aortic aneurysm.

BACKGROUND: Abdominal aortic aneurysm (AAA) accounts for approximately 45,000 deaths per year in the United States. Despite a striking male predominance of AAA (4:1 male to female), mortality from this disease is almost as high in women (20th leading killer of women and 15th leading killer of men in this country). OBJECTIVE: The purpose of this review is to highlight the differences in diagnosis, treatment, and treatment outcomes for women with AAA to determine avenues of potential improvement in their care. METHODS: Published articles relevant to this review were determined by the experience of the author, by PubMed and MEDLINE searches, and by reviewing the references cited in the reports identified by the first 2 methods. The database searches were performed using the following terms: abdominal aorta, aneurysm, gender, endovascular, and outcomes. Reports were limited to the English language and publication since 1995. RESULTS: Compared with men, women are older when their AAA is diagnosed and treated. Women have higher mortality than do men while undergoing elective open and endovascular repairs, and emergency surgery for ruptured AAAs. Owing to the anatomic complexity of their arterial anatomy, women are less frequently candidates for endovascular repair. Women receive treatment for rupture of AAA less frequently than do men. On Medicare induction, both men and women are eligible for a one-time screening for AAA; however, women qualify for this exam only if they have a family history of AAA. CONCLUSIONS: Opportunities to advance the care of women with AAA include improving screening techniques to find AAA prior to rupture and when women are younger and more likely to be candidates for repair. Current clinical practice should focus on decreasing mortality for open surgical repair and developing better endovascular devices so that anatomic obstacles can be overcome and more women can be candidates for this technology. In addition, furthering the understanding of gender differences in the pathophysiology of AAA disease may provide insights into treatments that could prevent the formation of aneurysms.

Limb stress-rest perfusion imaging with contrast ultrasound for the assessment of peripheral arterial disease severity.

OBJECTIVES: We hypothesized that stress-rest perfusion imaging of skeletal muscle in the lower extremity with contrast-enhanced ultrasound (CEU) could evaluate the severity of peripheral arterial disease (PAD). BACKGROUND: Perfusion imaging may provide valuable quantitative information on PAD, particularly in patients with diabetes in whom microvascular functional abnormalities are common. METHODS: Study subjects included 26 control subjects and 39 patients with symptomatic PAD, 19 of whom had type 2 diabetes mellitus. A modified treadmill exercise test was performed to determine exercise time to development of claudication. Multilevel pulse-volume recordings and ankle-brachial index (ABI) at rest and post-exercise ABI were measured in both extremities. Microvascular blood flow in the gastrocnemius and soleus muscles was measured at rest and after 2 min of calibrated plantar-flexion exercise. RESULTS: During exercise, claudication did not occur in normal subjects and occurred earlier in PAD patients with diabetes than without (median time 1.2 min [95% confidence interval (CI) 0.6 to 2.5] vs. 3.0 min [95% CI 2.1 to 6.0], p < 0.01). Compared to control subjects, patients with PAD had lower skeletal muscle blood flow during plantar-flexion exercise and lower flow reserve on CEU. After adjusting for diabetes, the only diagnostic tests that predicted severity of disease by claudication threshold were CEU exercise blood flow and flow reserve (odds ratios 0.67 [95% CI 0.51 to 0.88; p = 0.003] and 0.64 [95% CI 0.46 to 0.89, p = 0.008], respectively). A quasi-likelihood information analysis incorporating all non-invasive diagnostic tests indicated that the best models for predicting severity of disease were the combination of diabetes and either exercise blood flow or flow-reserve on CEU. CONCLUSIONS: Perfusion imaging of limb skeletal during exercise and measurement of absolute flow reserve can provide valuable information on the severity PAD. This strategy may be useful for evaluating the total impact of disease in patients with complex disease or those with coexisting functional abnormalities of flow regulation.

Calf muscle perfusion at peak exercise in peripheral arterial disease: measurement by first-pass contrast-enhanced magnetic resonance imaging.

PURPOSE: To develop a contrast-enhanced magnetic resonance (MR) technique to measure skeletal muscle perfusion in peripheral arterial disease (PAD). MATERIALS AND METHODS: A total of 11 patients (age = 61 +/- 11 years) with mild to moderate symptomatic PAD (ankle-brachial index [ABI] = 0.75 +/- 0.08) and 22 normals were studied using an MR-compatible ergometer. PAD and normal(max) (Nl(max); N = 11) exercised to exhaustion. Nl(low) (N = 11) exercised to the same workload achieved by PAD. At peak exercise, 0.1 mm/kg of gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) was infused at 3-4 cm(3)/second followed by a saline flush at the same rate. A dual-contrast gradient echo (GRE) sequence enabled simultaneous acquisition of muscle perfusion and arterial input function (AIF). The perfusion index (PI) was defined as the slope of the time-intensity curve (TIC) in muscle divided by the arterial TIC slope. RESULTS: Median workload was 120 Joules in PAD, 210 Joules in Nl(low), and 698 Joules in Nl(max) (P < 0.001 vs. Nl(low) and PAD). Median PI was 0.29 in PAD (25th and 75th percentiles [%] = 0.20, 0.40), 0.48 in Nl(low) (25th, 75th % = 0.36, 0.62; P < 0.02 vs. PAD), and 0.69 in Nl(max) (25th, 75th % = 0.5, 0.77; P < 0.001 vs. PAD). Area under the ROC-curve for PI differentiating patients from Nl(max) was 0.95 (95% confidence interval [CI] = 0.77-0.99). CONCLUSION: Peak-exercise measurement of lower limb perfusion with dual-contrast, first-pass MR distinguishes PAD from normals. This method may be useful in the study of novel therapies for PAD.

Diagnosis of aortoenteric fistulas with CT angiography.

PURPOSE: To describe the diagnostic findings of primary and secondary aortoenteric fistulas (AEFs) at computed tomographic (CT) angiography in a cohort of patients known to have AEF and to correlate those findings with those from endoscopic gastroduodenoscopy (EGD) and surgery. MATERIALS AND METHODS: CT angiography was performed in nine patients with AEF. There were four men and five women aged 43-85 years (mean age, 67 years). All CT angiograms were retrospectively reviewed for signs of AEF. Reports from EGD, surgery, and pathologic examination were also reviewed. RESULTS: One patient had a primary AEF, and eight patients had a secondary AEF. Findings at CT angiography were suggestive of the diagnosis in all nine patients. The two definitive CT angiographic findings were identification of the graft within the bowel lumen in two patients (22%) and active extravasation in one patient (11%), allowing the definitive diagnosis in three of the nine patients (33%). Secondary signs, which helped predict the high likelihood of the diagnosis but could also be seen in graft infection or inflammation without AEF, were as follows (in descending order of frequency): effacement of the periaortic or perigraft fat plane and the fat plane between the aorta and bowel (nine patients, 100%), perigraft soft tissue (nine patients, 100%), bowel wall thickening adjacent to the graft (eight patients, 89%), perigraft fluid (seven patients, 78%), perigraft hematoma (six patients, 67%), pseudoaneurysm or aneurysm bulge (six patients, 67%), ectopic gas (five patients, 56%), and dystrophic vascular graft calcification (one patient, 11%). The diagnosis was confirmed surgically in seven patients and with clinical follow-up in two. CONCLUSION: CT angiography is well suited for helping make or suggesting the diagnosis of AEF and is potentially more accurate than EGD.

CTA and MRA in mesenteric ischemia: part 2, Normal findings and complications after surgical and endovascular treatment.

OBJECTIVE: A number of surgical and endovascular options exist for the treatment of acute and chronic mesenteric ischemia. Both surgical and endovascular treatments necessitate close clinical and imaging follow-up because the consequences of acute occlusions can be catastrophic. MDCT angiography (CTA) and contrast-enhanced MR angiography (MRA) are the preferred imaging techniques in this setting. CONCLUSION: We review the appearance of the normal and complicated surgical and endovascular treatment on CTA and MRA.

Reproducibility and reliability of atherosclerotic plaque volume measurements in peripheral arterial disease with cardiovascular magnetic resonance.

A high resolution, noninvasive approach to quantify atherosclerotic plaque in the peripheral vasculature could have significant clinical and research utility. Seventeen patients with peripheral arterial disease (PAD) were studied in a 1.5T CMR scanner. Atherosclerotic plaque volume in the superficial femoral artery was measured and interobserver, intraobserver, and test-retest variability determined. Nineteen vessels were studied with mean acquisition time of 13.1 minutes per vessel. Mean plaque volume was 7.27 +/- 3.73 cm3. Intra-observer intraclass correlation was R = 0.997, inter-observer was R = 0.987, and test-retest reproducibility was R = 0.996. Thus, high resolution measurement of plaque volume in PAD is reliable and reproducible.