Contrast Enhanced MRA with Occlusion of the Left Iliac Arteries, Demonstrating TimCT and TWIST
author, Harald Kramer, MD
Clinical History:
This 56 year old woman presented to angiography with recurrent leg pain occurring with ambulation in excess of 200 meters. She had received a femorofemoral crossover bypass of the occlusions in the left common and external iliac arteries resulting from chronic aortic dissection.
Diagnosis:
Occlusion of the femorofemoral crossover graft with arterial supply to the distal left leg via extensive collateral vascularization.
MR Technique:
MRA images were acquired on a 3 T open bore MR System (Magnetom Verio, Siemens Medical Solutions, Erlangen, Germany) using a dedicated 36 element peripheral angiography array coil and a standard 6 element body surface coil in combination with a spine array coil integrated into the patient table. The MRA exam was performed using a continuous table movement technique (Syngo TimCT, TR/TE 2.8/1.1ms, reconstructed voxel size 1 x 1 x 1.3mm3, acquisition time 77 sec). Pre- and post-contrast images were acquired for later subtraction. After acquisition of the static MRA images a dynamic exam was performed covering the iliac region. Here a TWIST sequence (TR/TE 3.03/1.11 ms, spatial resolution 1.2 x 1.2 x 1.2 mm3, temporal resolution 2.16 sec) was used. 7.5 mL of 1.0 molar contrast agent were diluted to a volume of 30 ml with normal saline. 2 mL of this mixture were used as a test bolus for estimation of the contrast agent arrival time. 20 mL were utilized in the TimCT static MRA, and the residual 8 mL were used for time resolved TWIST MRA.
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Imaging Findings:
(A) Static TimCT MRA demonstrated occlusion of the both the crossover bypass graft and the left iliac arteries (external, internal and common). This is better demonstrated on the same scan, cropped to the area of interest (B). The graft origin is appreciated as the small, non-occluded vessel visualized in the middle of the right common femoral artery. On the right side, the iliac, thigh, and calf vessels are patent. On the left, the proximal and middle portions of the superficial femoral artery are patent, although there is vessel occlusion at its point of intersection with the popliteal artery. The vasculature within the left calf is again patent. Despite the occlusion of the crossover bypass graft, (C) dynamic TWIST MRA of the left iliac region demonstrates good collateral flow and no delay in contrast agent inflow to the superficial femoral artery as compared to the right. Flow distal to the occlusion of the left superficial femoral artery at its junction with the popliteal artery appears intact secondary to extensive collateralization with no delay in inflow to the calf vasculature as compared to the right.
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