Fast MR angiography of the aortoiliac arteries and arteries of the lower extremity: value of bolus-enhanced, whole-volume subtraction technique.

OBJECTIVE: MR angiography of the abdominal aorta and lower limb arteries has been hampered by the need to depict long segments of the arteries in short imaging times. To overcome these limitations, we combined fast acquisition of coronal sections with bolus-enhancement technique, subtraction, and whole-volume projection display. The purpose of this preliminary study was to determine the value of using this technique in patients with abdominal aortic lesions and atherosclerotic occlusive disease of the lower limbs. SUBJECTS AND METHODS: Ten healthy volunteers and 20 patients with abdominal aortic aneurysms (n = 15), vascular graft (n = 3), arteriovenous fistula (n = 1), and abdominal aortic dissection (n = 1) were examined by segmented K-space ultrafast gradient-echo sequences. Sequential 50-cm coronal sections were acquired before and after an IV bolus injection of gadolinium (0.1 mmol/kg). Subtraction images were created by subtracting precontrast from postcontrast images. In all MR images, signal intensity was measured in the aorta, the inferior vena cava, and the background tissues. The final MR angiogram was a summation image of each subtracted image and was compared with a preoperative conventional arteriogram. Data from each study were collected prospectively and analyzed in a blinded manner. The radiologist evaluated depiction of the following specific areas: the abdominal aorta, common iliac arteries on both sides, superficial femoral arteries and above-knee popliteal arteries, below-knee popliteal arteries, superior mesenteric artery, and renal arteries. The aneurysms were categorized as infrarenal or suprarenal and as involving or not involving the iliac arteries. The graft was considered patent if depicted at both its origin and its periphery.
RESULTS: In the healthy volunteers, bolus-enhanced subtraction MR angiography depicted without in-plane saturation the aorta, iliac arteries, and arteries of the lower extremity in less than 2 min. Gadolinium significantly increased the aortic signal-to-noise ratio from 25 +/- 3 to 232 +/- 8 (p < .0001), whereas the signal intensity of the inferior vena cava, muscles, and fat remained relatively stable. Examinations were thought to be interpretable in all but two patients. Clear delineation of aneurysms, intimal flap and arteriovenous fistula, and graft patency (n = 3) or occlusion (n = 2) were similarly diagnosed by conventional and MR angiography. Superior mesenteric artery was depicted in all cases on postcontrast images before subtraction. The number of renal arteries (n = 29) was correctly identified in all 15 patients who had renal areas included in their aortograms on postcontrast images before subtraction. However, renal arteries throughout their full length were usually obscured by renal veins and bowel contrast enhancement on the final MR angiogram. Furthermore, bolus-enhanced subtraction MR angiography was able to depict all lower limb arteries.
CONCLUSION: Although further evaluation and technical improvements are required, our preliminary results indicate that bolus-enhanced subtraction MR angiography is a promising new method for fast abdominal and peripheral vascular imaging.