Abstract Body (Do not enter title and authors here): Background
Rupture-prone high-risk atheromatous plaques are characterized by large plaque and positively remodeled necrotic core volumes and thin fibrous caps with significantly inflammation by the cells of monocyte-macrophage origin. The plaque volumes and remodeling are relatively reliably identified by noninvasive and invasive imaging, however; the detection of coronary inflammation is not conveniently possible. We propose that development of a radioisotope (RI) catheter could help record quantitative uptake of specifically targeted radiotracers against inflammation. counting of be developed.

Methods
We developed an RI catheter comprising scintillator and flexible optical fibers, with (sCath) and without (nsCath) shielding scintillator to obtain directionality and evaluated its utility in both in vitro and ex vivo experiments. For an in vitro study, the catheter was placed on ¹⁸F point sources to measure the radioactivity counts. For ex vivo study, atherosclerotic lesions were induced in 6 rabbits balloon injury model. Rabbits received ¹⁸F-fluorodeoxyglucose (FDG) and were sacrificed 2 hours later; the aortas were exposed, and RI catheter was pulled back every 1cm and counts measured the for 1 minute by nsCath, and right (sCath-R) and left (sCath-L) sided catheters. After 3 measurements, the artery was sectioned at 1cm and each segment was counted in an automatic well-type gamma-counter . Specimens were fixed overnight with 4% paraformaldehyde and serial sections were histologically analyzed and characterized immunohistochemically by anti-CD68 antibody for macrophage infiltration.

Results
In vitro study showed linear correlation between counts and ¹⁸F souse dose until at 100kBq (R²=0.996). For ex vivo study, 71 sections were obtained from 6 rabbits, and the cpm from each catheter was correlated with counts from well counter. The counts of both sCath-R and -L demonstrated the highest correlation (nsCath: r=0.47, sCath-R: r=0.42, -L: r=0.53, sCath-R+L: r=0.54, p<0.01, respectively), and showed excellent agreement with ipsilateral CD68-positive areas, CD68-L & sCath-L: r=0.50, CD68-R & sCath-R=0.42, p<0.01). The average CD68 area correlated with sCath-R+L, but not with nsCath (av. CD68 & sCath-R+L: r=0.44, p<0.01, CD68 average; nsCath: r=0.18, p=0.12).

Conclusions
The Shielded RI catheter counts correlated with well counts and ipsilateral CD68-positive area and are potentially useful for the detection of inflammation in high-risk plaques.