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An imaging system which simultaneously performs near infrared (NIR) tomography and magnetic resonance imaging (MRI) has been developed at Dartmouth College, to study breast tissue of women in vivo. A NIR image reconstruction technique which exploits the combined multi-wavelength data set is presented which implements the MR structure as a soft-constraint in the NIR property estimation. The benefits of spatial and spectral priors, applied independently and together, in NIR diffuse tomography image reconstruction of in vivo measurements are presented. When both spatial and spectral priors are applied in a healthy volunteer, glandular tissue shows higher total blood content, water, and scattering power compared to fatty tissue. 1