We report coregistration of near-infrared diffuse optical spectroscopy (DOS) and magnetic resonance imaging (MRI) for the study of animal model tumors. A combined broadband steady-state and frequency-domain apparatus was used to determine tissue oxyhemoglobin, deoxyhemoglobin, and water concentration locally in tumors. Simultaneous MRI coregistration provided structural (T<sub>2</sub>-weighted) and contrast-enhanced images of the tumor that were correlated with the optical measurements. By use of Monte Carlo simulations, the optically sampled volume was superimposed on the MR images, showing precisely which tissue structure was probed optically. DOS and MRI coregistration measurements were performed on seven rats over 20 days and were separated into three tumor tissue classifications: viable, edematous, and necrotic. A ratio of water concentration to total hemoglobin concentration, as measured optically, was performed for each tissue type and showed values for edematous tissue to be greater than viable tissue (1.2 ± 0.49 M/μM versus 0.48 ± 0.15 M/μM). Tissue hemoglobin oxygen saturation (StO<sub>2</sub>) also showed a large variation between tissue types: viable tissue had an optically measured StO<sub>2</sub> value of 61 ± 5%, whereas StO<sub>2</sub> determined for necrotic tissue was 43 ± 6%.
© 2003 Optical Society of America
Sean Merritt, Frederic Bevilacqua, Anthony J. Durkin, David J. Cuccia, Ryan Lanning, Bruce J. Tromberg, Gultekin Gulsen, Hon Yu, Jun Wang, and Orhan Nalcioglu, "Coregistration of diffuse optical spectroscopy and magnetic resonance imaging in a rat tumor model," Appl. Opt. 42, 2951-2959 (2003)