Intravascular near-infrared fluorescence (NIRF) imaging offers a new approach for characterizing atherosclerotic plaque, but random catheter positioning within the vessel lumen results in variable light attenuation and can yield inaccurate measurements. We hypothesized that NIRF measurements could be corrected for variable light attenuation through blood by tracking the location of the NIRF catheter with intravascular ultrasound (IVUS). In this study, a combined NIRF-IVUS catheter was designed to acquire coregistered NIRF and IVUS data, an automated image processing algorithm was developed to measure catheter-to-vessel wall distances, and depth-dependent attenuation of the fluorescent signal was corrected by an analytical light propagation model. Performance of the catheter sensing distance correction method was evaluated in coronary artery phantoms and ex vivo arteries. The correction method produced NIRF estimates of fluorophore concentrations, in coronary artery phantoms, with an average root mean square error of 17.5%. In addition, the correction method resulted in a statistically significant improvement in correlation between spatially resolved NIRF measurements and known fluorophore spatial distributions in ex vivo arteries (from r=0.24 to 0.69, p<0.01 , n=6 ). This work demonstrates that catheter-to-vessel wall distances, measured from IVUS images, can be employed to compensate for inaccuracies caused by variable intravascular NIRF sensing distances.
Intravascular near-infrared fluorescence (NIRF) imaging is a new approach for characterizing the physiological features
of atherosclerotic plaque, but random catheter positioning within the vessel results in non-quantitative measurements due to light attenuation through variable distances through blood. We hypothesized that the construction of a combined NIRF-intravascular ultrasound (IVUS) catheter would enable tracking of the catheter position within the blood vessel and permit corrections to NIRF measurements taken at variable distances from the vessel wall. In this study, a combined NIRF-IVUS catheter was designed, co-registered NIRF and IVUS data was acquired in vessel phantoms and ex vivo arteries, depth-dependent attenuation of the fluorescent signal was corrected by an analytical light propagation model. Average root-mean-square error between NIRF estimates of fluorophore concentrations and known concentrations of fluorescent targets in coronary artery phantoms improved from 94.9% to 16.2% following NIRF corrections. We demonstrate that catheter-to-vessel wall distances derived from IVUS imaging can be employed to correct for inaccuracies caused by random NIRF catheter sensing distances.