Rupture prone high-risk atheromatous plaques are characterized by large necrotic core volumes covered by thin fibrous caps which are positively remodeled; these plaques are significantly inflamed by the cells of monocyte-macrophage origin. We propose that the development of a position-sensitive positron-counting catheter, adding directionality with lead shields (sCath), would help record quantitative location-specific uptake of specifically targeted radiotracers against inflammation. For in-vitro study, the catheter was placed on 18F point sources to measure the radioactivity counts. For ex-vivo study, the 9 aortas dissected from the rabbit model of atherosclerosis were exposed, and catheters were pulled back every 1 cm and counts measured the for 1 min by non-shielded catheter (nsCath), sCath-R (right side) and sCath-L (left side). In-vitro study showed linear correlation between counts and 18F point source dose until at least 100 kBq (r = 0.98, p < 0.0001). In ex-vivo study, total 100 sections were obtained from 9 aortas and counts-per-minute (cpm) from each catheter nsCath, sCath-R, -L and the average of sCath-R and -L demonstrated high correlation coefficients with quantitative %ID/g (r = 0.49, 0.38, and 0.48, 0.48, respectively. p < 0.0001). They showed excellent agreement with ipsilateral macrophage numbers (sCath-R: r = 0.80, sCath-L: r = 0.73, p < 0.0001). Although the average macrophage numbers correlated with sCath-average of both sides (r = 0.80, p < 0.0001) and non-shielded Cath (nsCath) (r = 0.48, p < 0.0001), the positron count rate of sCath showed stronger correlation with ipsilateral macrohpage number. The directional superiority of sCath should potentially be useful in ecentric plaques for inflammation localization, compared with circumferential inflammatory load by the use of nsCath.
Nakahara et al. (Sun,) studied this question.