We developed a time-resolved reflectance diffuse optical tomography (RDOT) system to measure tumor responses to chemotherapy in breast cancer patients at the bedside. This system irradiates the breast with a three-wavelength pulsed laser (760, 800, and 830 nm) through a source fiber specified by an optical switch. The light collected by detector fibers is guided to a detector unit consisting of variable attenuators and photomultiplier tubes. Thirteen irradiation and 12 detection points were set to a measurement area of 50 × 50 mm for a hand-held probe. The data acquisition time required to obtain the temporal profiles within the measurement area is about 2 minutes. The RDOT system generates topographic and tomographic images of tissue properties such as hemoglobin concentration and tissue oxygen saturation using two imaging methods. Topographic images are obtained from the optical properties determined for each source-detector pair using a curve-fitting method based on the photon diffusion theory, while tomographic images are reconstructed using an iterative image reconstruction method. In an experiment using a tissue-like solid phantom, a tumor-like cylindrical target (15 mm diameter, 15 mm high) embedded in a breast tissue-like background medium was successfully reconstructed. Preliminary clinical measurements indicated that the tumor in a breast cancer patient was detected as a region of high hemoglobin concentration. In addition, the total hemoglobin concentration decreased during chemotherapy. These results demonstrate the potential of RDOT for evaluating the effectiveness of chemotherapy in patients with breast cancer.
Near-infrared spectroscopy (NIRS) has been used for noninvasive assessment of oxygenation in living tissue. For muscle measurements by NIRS, the measurement sensitivity to muscle (SM) is strongly influenced by fat thickness (FT). In this study, we investigated the influence of FT and developed a correction curve for SM with an optode distance (3 cm) sufficiently large to probe the muscle. First, we measured the hemoglobin concentration in the forearm (n=36) and thigh (n=6) during arterial occlusion using a time-resolved spectroscopy (TRS) system, and then FT was measured by ultrasound. The correction curve was derived from the ratio of partial mean optical path length of the muscle layer 〈LM〉 to observed mean optical path length 〈L〉. There was good correlation between FT and 〈L〉 at rest, and 〈L〉 could be used to estimate FT. The estimated FT was used to validate the correction curve by measuring the forearm blood flow (FBF) by strain-gauge plethysmography (SGP_FBF) and TRS (TRS_FBF) simultaneously during a reactive hyperemia test with 16 volunteers. The corrected TRS_FBF results were similar to the SGP_FBF results. This is a simple method for sensitivity correction that does not require use of ultrasound.
Using near-infrared time-resolved spectroscopy (TRS), we measured the human head in transmittance mode to obtain the
optical properties, tissue oxygenation, and hemodynamics of deep brain tissues in 50 healthy adult volunteers. The right
ear canal was irradiated with 3-wavelengths of pulsed light (760, 795, and 835nm), and the photons passing through the
human head were collected at the left ear canal. Optical signals with sufficient intensity could be obtained from 46 of the
50 volunteers. By analyzing the temporal profiles based on the photon diffusion theory, we successfully obtained
absorption coefficients for each wavelength. The levels of oxygenated hemoglobin (HbO<sub>2</sub>), deoxygenated hemoglobin
(Hb), total hemoglobin (tHb), and tissue oxygen saturation (SO<sub>2</sub>) were then determined by referring to the hemoglobin
spectroscopic data. Compared with the SO<sub>2</sub> values for the forehead measurements in reflectance mode, the SO<sub>2</sub> values of the transmittance measurements of the human head were approximately 10% lower, and tHb values of the transmittance measurements were always lower than those of the forehead reflectance measurements. Moreover, the level of
hemoglobin and the SO<sub>2</sub> were strongly correlated between the human head measurements in transmittance mode and the forehead measurements in the reflectance mode, respectively. These results demonstrated a potential application of this TRS system in examining deep brain tissues of humans.