Focal ICG deposition in rabbit atheroma evolves rapidly after injection and provides stable target-to-background ratios (TBRs). After ICG injection, serial NIRF guidewire pullbacks were performed in vivo through blood, with each pullback initiated distal to plaques and with the starting position confirmed by both IVUS and X-ray angiography. (A) The maximum plaque TBR was 10.4±6.2 in the rabbits (n=5) studied. *p<0.05, paired t-test, versus the maximum pre–ICG-injection TBR. (B) Immediately after ICG injection, the NIRF guidewire signal recorded a saturating signal (10 au) owing to high concentration of ICG in the blood, followed by a rapid exponential decay (upper inset). A representative baseline NIRF signal during manual guidewire pullback, prior to ICG injection is shown (below, left). Fifteen minutes (below, middle) and 25 minutes (below, right) after ICG injection, the NIRF signal presented focal peaks at the site of the atheroma, as visualized on corresponding X-ray angiograms and registered in real-time during X-ray fluoroscopic tracking of the radiopaque NIRF guidewire. Each data point depicts one measurement. The red line shows a best fit with an exponential decay of the data points from 10 to 33 minutes. (C) Over the course of the imaging session (approximately 45 minutes), the ICG peak plaque TBR remained stable (n=5). Error bars show the measurement error of each TBR data point.