Diffuse Optical Tomography (DOT) and Optical Spectroscopy using near-infrared (NIR) diffused light has demonstrated great potential for the initial diagnosis of tumors and in the assessment of tumor vasculature response to neoadjuvant chemotherapy. The NIR technique utilizes intrinsic hemoglobin contrast, which is directly related to tumor angiogenesis development, a key process required for tumor growth and metastasis. The NIR diffuse tomography holds great promise in distinguishing early-stage invasive breast cancers from benign lesions. This technique also provides insight into tumor metabolism and tumor hypoxia, important indicators of tumor response to various forms of therapy. Currently, the high cost of the DOT system is mainly because of three components, the cost of laser diodes, the cost of optical switches, and the cost of detectors, Photon Multiplier Tubes (PMT). With recent advances in photonics, the performance of light-emitting diodes (LEDs) is becoming increasingly comparable in terms of output power and spectral width. One of the most appealing strengths of LEDs is the cost, which is several dollars at a similar output power level as that of laser diodes. Besides, LEDs have demonstrated to be safer and more reliable in medical use due to their high resistance to physical lacerations, heat, and electrical damage. Because of the low cost of LEDs, multiple sources can be installed simultaneously. As a result, the expensive and fragile optical switch can be eliminated. On the detector side, silicon-based avalanche photodiodes (APDs) have the advantage of low cost, similar or even better sensitivity and resolution in the red and near-infrared spectral regions. The aims of this project are 1) to test the different types of LEDs in near-infrared range, and design the driving circuit, and test the modulation of LEDs at different frequencies; 2) to test the APDs as detector, and build the receiver system, test the light coupling, and compare the efficiency with PMT.