Visualization and quantitation of atherosclerotic plaque in the lower extremities is a relatively new area of MRI investigation (9
). The diameter of the leg is much less than that of the body trunk, making smaller, more efficient coils conducive to improved signal detection in the legs. The legs can also be immobilized and are less likely to generate motion artifacts compared to other vessels, such as the carotids. Correspondingly, in vivo imaging of the lower extremity vessels can have advantages of high SNR and image quality, allowing reliable measurements of atherosclerotic lesions. This study has focused on developing fast and reliable peripheral vessel imaging technology.
A major challenge in clinically relevant SFA atherosclerosis imaging is sampling an adequately large FOV in the head–foot direction. Since there may be multiple lesions dispersed throughout the SFA, it is desirable to cover the area from the profunda to the popliteal. Our early studies utilized a single channel loop coil with 6 cm diameter for signal reception; although the images obtained with this coil were of good quality, it lacked the desired coverage in the head–foot direction and did not offer bilateral imaging. We have overcome both of these deficiencies by fabricating a custom coil that covers the full length of the right and left SFA. This affords the advantage of directly comparing an atheroma in the index SFA with the corresponding site on the contralateral artery, whereas image registration required for two unilateral images make such a comparison inconvenient. Although the bilateral coil affords these important benefits, its 18 cm diameter can accommodate the legs of a patient of average size and weight (<200 lbs), but can be restrictive for larger patients. This confinement can lead to involuntary leg muscle twitching during an extended imaging session (>45 min) which may generate image artifacts.
In this work, conventional spatial saturation provided only marginal blood suppression, and in some cases compromised the delineation of the vessel wall. While spatial saturation may provide adequate suppression of blood signal in arteries with fast-moving blood such as the aorta, slower blood flow in the lower extremities (34
) may limit its effectiveness, especially during a multislice or volumetric acquisition. SFA vessel wall delineation may be improved by implementing advanced blood suppression techniques such as T2 prepared inversion recovery (35
) or motion-sensitizing magnetization preparation (37
In conclusion, the clinical utility of the new bilateral coil was demonstrated by addressing three specific aims: 1) to resolve the relatively small SFA vessel wall structure over an FOV extending from the profunda to the popliteal; 2) to acquire a complete set of TOF, T1w, T2w, and PDw images from both legs in a reasonable examination time; and 3) to compare diseased and contralateral vessels in the same patient. Each of these aims has been addressed, indicating the potential of this coil for noninvasive detection of atherosclerotic lesions and for the monitoring of their progression, stabilization, and regression over time in multiple arterial sites.