Abstract 2538: T1-Weighted Turbo Spin Echo Cardiovascular Magnetic Resonace Imaging Shows a Significant Increase in Signal after SPIO Administration in Human Carotid Atherosclerotic Plaques
Introduction. A limitation of gadolinium (Gd) enhanced MRI is the inability to discriminate fibrosis from inflammation. Small paramagnetic iron oxide (SPIO) has been used for inflammation imaging since macrophages phagocytose SPIO particles. Low concentration of SPIO causes increased signal on T1 images. We hypothesize that activated macrophages in plaques phagocytose and retain SPIO.
Methods. Five patients awaiting carotid endarterectomy were imaged on a 1.5T clinical scanner (Siemens Avanto) with a commercial neck matrix coil. The T1w TSE sequence was a black blood, 2D Turbo spin echo sequence with a TR/TE=1500msec/10msec, FoV=179 mm, matrix size 320x320, slice thickness 3 mm, 3 averages. Subjects were scanned prior to (Panel A) and after infusion of clinical dose of SPIO (30 min; Panel B; 24 hours, Panel C) and Gd (Panel D). Images were magnified two-fold, normalized to air and signal measurements made using NIH ImageJ. Tissue samples were prepared from harvested plaque in standard fashion. Statistics were performed using the student’s t test.
Results. The mean values of the normalized T1w signal are demonstrated on panel E. Both the post-SPIO (7.82 vs 5.8; P=0.024) (Panel B) and post-Gd values (9.27 vs 5.8; P=0.002) (Panel D) are statistically greater than the pre-contrast signal. Iron was detected in the inflammatory domain (panel F). SPIO particles were then demonstrated to be within macrophages by TEM (panel G).
Conclusion. The expected signal increase post-Gd infusion was significant. The significant increase in signal following SPIO infusion suggested the presence of inflammation which was confirmed by histology and TEM.