Relying on deeper penetration of light in the tissue, Diffuse Optical Tomography (DOT) achieves organ-level
tomography diagnosis, which can provide information on anatomical and physiological features. DOT has been widely
used in imaging of breast, neonatal cerebral oxygen status and blood oxygen kinetics observed by its non-invasive, security
and other advantages.
Continuous wave DOT image reconstruction algorithms need the measurement of the surface distribution of the
output photon flow inspired by more than one driving source, which means that source coding is necessary. The most
currently used source coding in DOT is time-division multiplexing (TDM) technology, which utilizes the optical switch to
switch light into optical fiber of different locations. However, in case of large amounts of the source locations or using the
multi-wavelength, the measurement time with TDM and the measurement interval between different locations within the
same measurement period will therefore become too long to capture the dynamic changes in real-time.
In this paper, a frequency division multiplexing source coding technology is developed, which uses light sources
modulated by sine waves with different frequencies incident to the imaging chamber simultaneously. Signal corresponding
to an individual source is obtained from the mixed output light using digital phase-locked detection technology at the
detection end. A digital lock-in detection circuit for photon counting measurement system is implemented on a FPGA
development platform. A dual-channel DOT photon counting experimental system is preliminary established, including the
two continuous lasers, photon counting detectors, digital lock-in detection control circuit, and codes to control the
hardware and display the results. A series of experimental measurements are taken to validate the feasibility of the system.
This method developed in this paper greatly accelerates the DOT system measurement, and can also obtain the multiple
measurements in different source-detector locations.