Spatial resolution in depth for time-resolved diffuse optical tomography using short source-detector separations

Abstract

Diffuse optical tomography for medical applications can require probes with small dimensions involving short source-detector separations. Even though this configuration is seen at first as a constraint due to the challenge of depth sensitivity, we show here that it can potentially be an asset for spatial resolution in depth. By comparing two fiber optic probes on a test object, we first show with simulations that short source-detector separations improve the spatial resolution down to a limit depth. We then confirm these results in an experimental study with a state-of-the-art setup involving a fast-gated single-photon avalanche diode allowing maximum depth sensitivity. We conclude that short source-detector separations are an option to consider for the design of probes so as to improve image quality for diffuse optical tomography in reflectance.

New frontiers in time-domain diffuse optics, a review

“…At any rate, this technology has been considered within recent years [69][70][71][72]97,106,107 because it is the only one presently allowing the exploration of new physical concepts like the null source-detector separation and measurement schemes based on the dense arrangement of optodes. 73 We already discussed in Sec.…”

Characterization of a time-resolved non-contact scanning diffuse optical imaging system exploiting fast-gated single-photon avalanche diode detection

“…Indeed, in reflectance geometry, photons that are collected within a few hundreds of picoseconds with respect to the time of injection of the laser pulse have travelled only in a superficial region, whereas after 1 ns depths greater than 1 cm can be explored. 17,18 It has also been demonstrated that by using a quasi-null source-detector distance, an improvement of spatial resolution and an increase in the amount of detected photons at all times are obtained. 19 The main disadvantage of this technique is the huge increase (with respect to larger source-detector distance) of the peak of early photons causing saturation of the detection electronics.…”

Time-domain diffuse optical tomography using silicon photomultipliers: feasibility study

“…2 However, only the TD approach has the added advantage of encoding different average penetration depths in the photon arrival time. 7,8 Therefore, a time-gated analysis 9 and/or detection 10,11 of the reflectance curve allows one to separate information coming from different layers of the investigated medium. The use of the photon arrival time as an additional information to differently weight spatial regions explored by the photons also leads to ideally better image quality with respect to other techniques, 12 as well as to lower dependence on moving artifacts.…”

“…Indeed, DOT can involve long acquisition times, in particular, when tomographic reconstructions are obtained by scanning the tissue surface instead of using a multichannel system. 10 The aim of this paper is to address these issues and demonstrate the suitability of SiPMs for optical tomography in the TD. In particular, we have studied on tissue-mimicking heterogeneous phantoms (using absorbing inclusions at different depths), the sensitivity of SiPMs to deep perturbations into the medium and their capability to properly localize and reconstruct buried inclusions.…”