Role of late photons in diffuse optical imaging

Abstract

The ability to image through turbid media, such as organic tissues, is a highly attractive prospect for biological and medical imaging. This is challenging, however, due to the highly scattering properties of tissues which scramble the image information. The earliest photons that arrive at the detector are often associated with ballistic transmission, whilst the later photons are associated with complex paths due to multiple independent scattering events and are therefore typically considered to be detrimental to the final image formation process. In this work, we report on the importance of these highly diffuse, "late" photons for computational time-of-flight diffuse optical imaging. In thick scattering materials, >80 transport mean free paths, we provide evidence that including late photons in the inverse retrieval enhances the image reconstruction quality. We also show that the late photons alone have sufficient information to retrieve images of a similar quality to early photon gated data. This result emphasises the importance in the strongly diffusive regime of fully time-resolved imaging techniques.

High resolution TCSPC imaging of diffuse light with a one-dimensional SPAD array scanning system

“…Time-correlated imaging can be used to observe the progression of light through highly scattering media for imaging applications [12][13][14][15]. For example, time-resolved imaging of light emission from a point source suspended within scattering media has the potential to infer the location of that source [11].…”

“…However, here a compromise was made to provide sufficient signal to noise to allow reliable automatic processing of data. In future more advanced processing of earlier photon arrivals, or indeed analysis including later photon arrivals [15], could be employed. , where all point locations (blue stars) were recovered in proximity to the known locations (red triangles).…”

“…We suggest the ability to locate fibre devices deep within scattering media is relevant to medical device location as previously described [11], we build upon this by offering improved light detection capability and device path observation rather than a single point. The improved time-resolved imaging of diffuse photons has application in further environments [12][13][14][15].…”

Coherence-gated digital holographic imaging through extended scattering media for autonomous driving vehicles

“…It should be mentioned that there are approaches where object information may be extracted from multiple scattered photons. [14][15][16] However, these techniques require precise knowledge of the scattering medium and are extremely impractical for extended bodies of scattering media (several meters and beyond). To increase the imaging range through scattering media without increasing the illumination power (thus maintaining eye-safety), technologies providing a higher SNR need to be incorporated.…”

Near-Infrared 3D Imaging with Upconversion Detection

“…Some other optical techniques are also present in the literature to address imaging through multi-scattered media. Most of these techniques can be broadly classified as relying on ballistic photons [39,46], diffuse optical tomography [47,48], etc. Those techniques offer potential applications for medical imaging, communications and security [2,49].…”