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This paper describes the design of an improved multichannel time-domain diffuse optical tomography (TD-DOT) system. For the spread spectrum TD-DOT, the image quality depends on the stability of the time-resolved signals, which can be affected by fluctuation in the source modulation depth and drift in the detector gain. A microcontroller-based bias controller is designed to lock the bias of a Mach-Zehnder intensity modulator at the positive quadrature point. With additional temperature stabilization over the avalanche photodiodes, the temporal stability of the time-resolved signals has been significantly improved-the fluctuations of the temporal point spread function have been limited to ±2% for a testing period of a few hours. The image quality and reproducibility have been substantially improved with the stabilized signals.