Abstract
We present the first experimental results of reflectance Diffuse Optical Tomography (DOT) performed with a fast-gated single-photon avalanche diode (SPAD) coupled to a time-correlated single-photon counting system. The Mellin-Laplace transform was employed to process time-resolved data. We compare the performances of the SPAD operated in the gated mode vs. the non-gated mode for the detection and localization of an absorbing inclusion deeply embedded in a turbid medium for 5 and 15 mm interfiber distances. We demonstrate that, for a given acquisition time, the gated mode enables the detection and better localization of deeper absorbing inclusions than the non-gated mode. These results obtained on phantoms demonstrate the efficacy of time-resolved DOT at small interfiber distances. By achieving depth sensitivity with limited acquisition times, the gated mode increases the relevance of reflectance DOT at small interfiber distance for clinical applications.
Highlights
Diffuse Optical Tomography (DOT) was developed in the 1990’s for medical imaging with potential applications including mammography or functional brain activity monitoring
In this article we show that the signals acquired with fast-gated single-photon avalanche diode (SPAD) combined with time-correlated single photon counting (TCSPC) enable the reconstruction of maps of μa coefficients in the medium by using analysis methods requiring the full temporal point spread function (TPSF) like the Mellin-Laplace transform
The perfect overlap of all homogeneous measurements at both interfiber distances for non-gated and gated acquisitions confirms that the differences between TPSFs measured for different depths of the inclusion are due to the position of the inclusion and not due to experimental drifts
Summary
Diffuse Optical Tomography (DOT) was developed in the 1990’s for medical imaging with potential applications including mammography or functional brain activity monitoring. A few geometries enable transmittance measurements through tissue and yield information on the whole tissue volume. This is the case of mammography with cylindrical or spherical arrangements of sources and detectors around the breast or of brain imaging of premature infants with helmets of optical fibers [1,2]. For the widespread category of DOT instruments using continuous wave sources and detection, depth sensitivity is addressed by using large interfiber distances between sources and detectors so that the majority of collected photons probe deep layers of the tissue. The use of small interfiber distances can make the diagnostic procedure more practical, enabling the use of optical probes which are more easy-to-handle than helmets or cylinders of optical fibers which require perfect positioning in order to achieve proper image reconstruction (e.g. for brain measurements [6])
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