Rapid near-infrared diffuse tomography for hemodynamic imaging using a low-coherence wideband light source

Rapid near-infrared (NIR) diffuse optical tomography is implemented using a low-coherence source. The spectral bandwidth of the low-coherence source is dispersed and coupled to linearly bundled fibers, such that "spread"-spectral encoding among the bundled fibers is formed, and could be used for parallel source illumination onto tissue. In comparison with a previous spectral-encoding technique that employed multiple laser diodes, the use of a low-coherence source for spread-spectral encoding presents a few unique characteristics: (1) it provides shift-free spectral encoding; (2) it reduces the reconstruction uncertainty significantly owing to the minimization of spontaneous channel-to-channel intensity fluctuation; and (3) it enables the implementation of NIR tomography into an endoscopic imaging mode. A 20-mW superluminescent diode centered at 840 nm with a 40-nm bandwidth is used as the source, and a sampling speed of 5 Hz is obtained in a 27-mm imaging array consisting of eight sources and eight detection channels. The principles of using a low-coherence source for spread-spectral encoding are elaborated, the characteristic performances are demonstrated, and the preliminary results of imaging hemoglobin absorption variations during 10 s of voluntary breath-holding are presented.