Abstract
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 (T2-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/microM versus 0.48 +/- 0.15 M/microM). Tissue hemoglobin oxygen saturation (StO2) also showed a large variation between tissue types: viable tissue had an optically measured StO2 value of 61 +/- 5%, whereas StO2 determined for necrotic tissue was 43 +/- 6%.
Highlights
The development of noninvasive diagnostic techniques to image and characterize physiological properties of tissues is an area of intense research and clinical interest
Through the use of MRI contrast agents these studies access functional tissue information, which is key to understanding physiology
The fit of the chromophore spectraHb, HbO2, H2O, and constant background absorptionto the a spectrum allows for the determination of the concentrations
Summary
The development of noninvasive diagnostic techniques to image and characterize physiological properties of tissues is an area of intense research and clinical interest. Such diagnostic tools are crucial for the study of tumor physiology and in particular angiogenesis. DOS can be used to measure chromophore concentrations such as oxy- and deoxyhemoglobinHbO2 and Hb, respectively, waterH2O, and fat within a local volume of tissue, Received 6 September 2002; revised manuscript received 2 December 2002. The literature documenting the use of MRI to monitor tumor growth and response to therapy is extensive.[3,4,5,6] Through the use of MRI contrast agents these studies access functional tissue information, which is key to understanding physiology. Another example of a widely used contrast agent is Gadopentate dimeglumineGd-DTPA, which allows for the determination of vascular volume fraction.[6]
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