Combining near infrared tomography and magnetic resonance imaging to improve breast tissue chromophore and scattering assessment

This work describes a multi-spectral frequency domain Near Infrared (NIR) tomography system which was constructed specifically for operation inside the high magnetic fields presented by Magnetic Resonance Imaging (MRI). The combined platform is used to image breast tissue morphology and function simultaneously. Image reconstruction algorithms are outlined which incorporate a priori knowledge of breast tissue structure from MRI that could potentially improve the resolution and overall efficacy of NIR tomography. NIR spectroscopic imaging systems are used to estimate spatially resolved distributions of hemoglobin concentration and oxygenation, water, and light scattering in tissue, thereby localizing functional changes which may occur at centimeter depths. Due to the diffusive nature of NIR light propagation in tissue, computational model-based image reconstruction methods are used to provide the spatial resolution and quantification for the chromophore concentrations and scattering parameters sought. Optimizing spatial resolution is an important concern in research and clinical applications, and the combination with MRI is an important part of this. This NIR-MRI imaging system and its complimentary modeling tools have been tested and optimized using data collected from tissue-simulating phantoms, and used to study the properties of component normal breast tissues in vivo for a pilot population of women. Total hemoglobin concentration, hemoglobin oxygen saturation, water fraction, scattering amplitude, and scattering power were estimated for adipose tissue [17 μM, 71%, 47%, 1.3, and 0.6, respectively] and fibroglandular tissue [22 μM, 70%, 60%, 0.9, and 0.8, respectively]. Images with millimeter resolution and high contrast can be reconstructed which may provide indicators of functional activity and disease processes.