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Multichannel single-photon-counting NIR imager for coregistration with MRI

An effective way to investigate the competence of NIR Imaging is to associate NIR images with ones from other, well established modalities, such as X-ray Mammography, Tomography or Magnetic Resonance Imaging (MRI). MRI is an excellent candidate for such an approach since besides having immense sensitivity and rendering great anatomical information, it also employs non-ionizing radiation. The simultaneous acquisition of MR and NIR data may afford very precise co-registration of images and investigate the potential and limitations of the technique. In return, by establishing confidence on the NIR Tomography capability, the MR specificity may be enhanced due to the additional information content of the simultaneous examination. We have developed a 24 X 8 source-detector multi-channel NIR imager and spectrometer based on the time-correlated single photon counting technique. The instrument is capable of operating as a stand-alone modality or coupled to an MR scanner. We have tested the instrument as a breast imager with volunteers and patients in the MR examination room. We have used specially designed soft compression plates bearing the optical fibers and the MR coils. The acquisition time has been optimized to be within the time limits of a typical MR breast examination protocol. We have obtained approximately 25 dB signal to noise ratio per sec of averaging time for 6 cm breast separation and sensitivity of absorption coefficient changes, following contrast agent administration, of the order of 10-3 cm-1. Additionally we demonstrate the use of the instrument as a stand-alone motor cortex activity imager/spectrometer.