Diffuse optical tomography (DOT) is a noninvasive imaging technique in which near-infrared light is used to probe the interior of the body for oxygenation and other physiological changes. Applications include brain monitoring, optical mammography, and diagnostic imaging of joints and limbs.

A major challenge in optical imaging of biological tissue is the strong scattering of visible and infrared light by tissue. Unlike x-rays, low-energy photons do not travel through the body in a straight line, but instead propagate in a diffuse manner and thus carry little spatial information about the volume. DOT systems deal with this situation by using an array of detectors to sample as much reflected light as possible over a surface area, and then processing this information with statistical models of photon transport to generate cross-sectional or 3-D images of the tissue. In addition to structural data, these images provide functional information about the tissue, which can be derived from the typical absorption spectra of specific molecular species such as oxy- and deoxyhemoglobin.

DOT systems use various types of measurement methods, including frequency domain measurement, continuous wave measurement, and time-resolved methods such as time-correlated photon counting. Measurements are mostly made at wavelengths between 750 nm and 1000 nm. Typically, detectors placed close to the light source will detect light scattered from tissue just below the surface, while detectors placed further away will detect light from deeper tissue where the signal is very weak. Imaging deeper tissue thus requires detectors with high sensitivity and wide dynamic range. Detectors should also have excellent time or frequency response in order to discriminate between surface scattering and deep-tissue scattering.

• H9305-03 compact PMT module: spectral response from 18 to 900 nm. High-sensitivity type.
• H7546B PMT module: 64-channel PMT module with spectral response from 300 to 650 nm.
• H7422P-50 PMT module: spectral response from 380 to 890 nm. High-gain type for photon counting.
• R3896 28 mm side-on PMT: high-sensitivity multialkali photocathode with spectral response from 185 to 900 nm.
• C5658 APD module: includes avalanche photodiode with 1 GHz response speed and high sensitivity.
• C5331 series APD modules: operates the built-in avalanche photodiode with a single 5 V power supply. Spectral response from 400 to 1000 nm or 200 to 1000 nm.
• S2387 series silicon photodiodes: visible to near-infrared range, low dark current.
• S1337 series silicon photodiodes: UV to near-infrared sensitivity, low dark current.
• Orca AG deep-cooled digital camera (C4742-80-12AG): high-sensitivity camera with high-resolution progressive scan CCD. Wide dynamic range. For low-light imaging in the visible to near-infrared spectrum.

Please contact us for information on other products which can be used for this application.