Characterization of signal properties in atherosclerotic plaque componentsby intravascular MRI

Magnetic resonance imaging (MRI) is capable of distinguishing between ather osclerotic plaque components solely on the basis of biochemical differences . However, to date, the majority of plaque characterization has been perfor med by using high-field strength units or special coils, which are not clin ically applicable. Thus, the purpose of the present study was to evaluate M RI properties in histologically verified plaque components in excised human carotid endarterectomy specimens with the use of a 5F catheter-based imagi ng coil, standard acquisition software, and a clinical scanner operating at 0.5 T. Human carotid endarterectomy specimens from 17 patients were imaged at 37 degrees C by use of an opposed solenoid intravascular radiofrequency coil integrated into a 5F double-lumen catheter interfaced to a 0.5-T Gene ral Electric interventional scanner. Cross-sectional intravascular MRI (156 x 250 mu m in-plane resolution) that used different imaging parameters per mitted the calculation of absolute T1 and T2, the magnetization transfer co ntrast ratio, the magnitude of regional signal loss associated with an inve rsion recovery sequence (inversion ratio), and regional signal loss in grad ient echo (gradient echo-to-spin echo ratio) in plaque components. Histolog ical staining included hematoxylin and eosin, Masson's trichrome, Kossa, oi l red O, and Gomori's iron stain. X-ray micrographs were also used to ident ify regions of calcium. Seven plaque components were evaluated: fibrous cap , smooth muscle cells, organizing thrombus, fresh thrombus, lipid, edema, a nd calcium. The magnetization transfer contrast ratio was significantly les s in the fibrous cap (0.62 +/- 13) than in all other components (P < 0.05) The inversion ratio was greater in lipid (0.91 +/- 0.09) than all other com ponents (P < 0.05). Calcium was best distinguished by using the gradient ec ho-to-spin echo ratio, which was lower in calcium (0.36 +/- 0.2) than in al l plaque components, except for the organizing thrombus (P < 0.04). Absolut e T1 (range 300 +/- 140 ms for lipid to 630 +/- 321 ms for calcium) and T2 (range 40 +/- 12 ms for fresh thrombus to 59 +/- 21 ms for smooth muscle ce lls) were not significantly different between groups. In vitro intravascula r MRI with catheter-based coils and standard software permits sufficient sp atial resolution to visualize major plaque components. pulse sequences that take advantage of differences in biochemical structure of individual plaqu e components show quantitative differences in signal properties between fib rous cap, lipid, and calcium. Therefore, catheter-based imaging coils may h ave the potential to identify and characterize those intraplaque components associated with plaque stability by use of existing whole-body scanners.