Prototype miniature endoluminal MR imaging catheter

The feasibility of a miniature endoluminal magnetic resonance (MR) detection coil was investigated for imaging mural and perimural anatomy of small, tubular structures.

To this end, remotely tunable, single-loop, multiturn, receive-only radio-frequency coils, housed in 6-9-F arterial sheaths, were built. A 1.9-T imager was used. Phantom excitation was accomplished with a 62-mm-diameter bird-cage quadrature coil, and ex vivo specimen excitation was accomplished with a single-turn, untuned wire loop. Phantom images obtained with use of a 9-F catheter coil showed a signal-to-noise improvement on the border of 20 dB compared with images obtained with the quadrature coil. An 8-F catheter coil was used to obtain high-resolution (100 microns in-plane pixel size, 500 microns section thickness) spin-echo images (repetition time = 2,400 msec, echo time = 53 msec) of the wall of a fresh ex vivo human popliteal artery.

Prospectively, these images were suggestive of the presence of diffuse intimal hyperplasia, medial calcification, and focal atherosclerotic plaque. These findings were confirmed histologically. Three-dimensional restacking of the axial images simplified examination of the normal layers and pathologic changes within the wall. The improved signal-to-noise characteristics of these miniature coils permit fast high-resolution imaging, allowing visualization of microscopic anatomic details.

With further development, this technology may be useful for studying atherosclerosis and for providing imaging guidance during endoluminal MR interventions.