Improving Pedal Revascularization
Improving Pedal Revascularization
Abstract & Commentary
Synopsis: MR angiography is significantly more accurate for identifying patent pedal arteries, minimizing the necessity for lower extremity amputations by allowing viable bypass procedures to be performed.
Source: Kreitner KF, et al. Diabetes and peripheral arterial occlusive disease: Prospective comparison of contrast-enhanced three-dimensional MR angiography with conventional digital subtraction angiography. AJR Am J Roentgenol 2000;174:171-179.
For patients suffering from the complications of diabetes, the visualization of pedal arteries are of particular importance for determining therapeutic options that might mean the difference between losing a leg. It has been recognized for some time that digital subtraction arteriographic techniques, selective or non-selective, may falsely imply that pedal arterial vessels are occluded. The identification of patent pedal arteries is critical for successful bypass surgery to maintain arterial flow to the foot allowing healing of foot ulcers and osteomyelitis, alleviating substantial ischemia, and, thus, avoiding amputation.
In the January 2000 issue of the American Journal of Roentgenology, Kreitner and colleagues report on the dedicated use of gadolinium enhanced three-dimensional magnetic resonance angiography (MRA) for the assessment of the pedal arteries in diabetic peripheral arterial occlusive disease. This study is noteworthy because they have focused specifically on the identification of patent pedal arteries, and have sought to ascertain the relative use of MRA vs. digital subtraction angiography (DSA) for this important clinical assessment.
Twenty-four patients with diabetes mellitus and severe peripheral arterial occlusive disease were consecutively recruited for the study. All patients had both MRA and DSA within five days. MRA was performed on the symptomatic foot using a transmit-receive head coil and standard 1.5 T full body imager. A high performance (25 mT/m) gradient that enabled a 600-msec rise time was used in order to perform imaging of a 90 mm thick volume subdivided into 40 sagittal partitions (2.25-mm thick) with in-plane matrices of 150 × 256 or 170 × 512 thickness. Acquisition time was 18 or 25 sec for each of four sequential volumetric acquisitions. All patients received an intravenous injection of 20 mL of gadopentetate dimeglumine. This approach allowed for imaging without preliminary timing bolus and compensated for intra individual variations in circulation time such that maximal arterial opacification was observed during the second, third, or, in two cases, the fourth imaging volume. The data were processed with digital subtraction technique whereby an unenhanced preliminary data set (first volume acquisition) was subtracted from the contrast-enhanced data sets. These images were then evaluated relative to DSA images, which were acquired using both selective and nonselective techniques.
Of a possible 168 segments, 30 vessel segments were seen exclusively on MR angiograms; however, in no cases were patent vessels identified exclusively by DSA. These differences were statistically significant, particularly for visualization of inframalleolar vessels including the dorsal pedal artery, lateral plantar arteries, and pedal arch. Further, the significance of these results were independent of the use of selective vs. nonselective DSA technique. When analyzed on a per patient basis, MRA demonstrated a patent vessel that was suitable for distal bypass grafting in nine of 24 patients where DSA failed to document a patent vessel. This led to a change of treatment plan in seven patients, with two patients receiving a pedal bypass graft instead of amputation of the lower extremity below the knee and five patients undergoing femoropedal bypass grafting instead of femoropopliteal bypass grafting.
In 14 of the 24 patients, diagnostic quality postoperative fine needle DSA was performed for bypass control and served as a reference standard to the preoperative imaging tests. This test documented that there were no false-positive findings (occluded branches) on the MR angiograms. In a head-to-head comparison of overall image quality between the DSA and MRA images, three observers rated the MRA superior to DSA in 39 instances, equivalent in 32 instances, and DSA images superior to MR images in only one instance.
Comment by Geoffrey d. Rubin, MD
The fundamental value of this study is that it establishes that regardless of the imaging test used for assessing lower extremity inflow and proximal runoff, in situations of severe distal occlusive disease and, in particular, diabetic patients with limb-threatening ischemia, a dedicated MR angiogram to assess the pedal arteries is significantly more useful than DSA alone for determining the most effective and least debilitating therapy.
One criticism of this study is worth bringing to light. Because the population was composed exclusively of diabetic patients, there was a desire to minimize iodinated contrast use at DSA; therefore, repeated injections were not performed to assess equivocal sites. This might result in less overall diagnostic accuracy for DSA as it might be applied to patients without diabetes who can tolerate higher iodine doses. However, patients with limb-threatening ischemia due to distal lower extremity occlusive disease are typically diabetic, where the liberal use of iodinated contrast can result in substantial renal morbidity.
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