High-speed light source depth estimation using spatially-resolved diffuse imaging

Abstract

We describe a system for high-speed depth estimation of a light source embedded in a scattering medium. A polynomial model estimates source depth from the spatially-resolved, diffuse reflectance profile measured with a fibre optic probe on the surface of a scattering medium. A dataset of Monte Carlo reflectance profiles is generated over a range of typical optical properties and the model is fit to the simulated reflectance at four detector locations. The model accounts for a source depth up to 15mm. Cross-validation using the Monte Carlo dataset produced a root mean square error of 0.12mm. Experimental reflectance data is acquired with the detector probe, which consists of four optical fibres mounted in a black acetal plastic disk. The optical fibres are coupled into avalanche photodiodes for high-speed acquisition of the reflectance profile. When applied to measurements from a tissue-mimicking phantom with an embedded light source, the polynomial model generates depth estimates within 2mm of the true depth, up to a source depth of 15mm.

Spatially resolved diffuse imaging for high‐speed depth estimation of jet injection

“…Furthermore, depth estimates were produced using the surface profile sampled at only four radial distances. The method is therefore applicable to measurements from a previously developed fiber optic probe, specifically designed for the high‐speed acquisition required during a jet injection . Once implemented in real time, this system could provide the means of delivering fluid to the subcutaneous fat, which typically resides from between 2 and 15 mm beneath the skin surface.…”

“…For this, measurements of the surface profile were used from only four radial distances: 3, 5, 7 and 9 mm from the insertion point of the source. This was done to be consistent with the detector configuration of a previously developed fiber optic probe, capable of very high‐speed acquisition .…”

“…Estimating light source depth using this method has received less attention, with some studies determining the depth of a light source by inverting an analytical diffusion model of light propagation . We have also previously shown it is possible to recover source depth with a fiber‐based detector probe using a polynomial model fitted to a dataset generated from Monte Carlo simulations . The polynomial model produced depth estimates within 2 mm of the true source down to a depth of 15 mm in tissue‐mimicking phantoms.…”

Classification of diffuse light emission profiles for distinguishing skin layer penetration of a needle-free jet injection

“…The inputs to the model, the predictor variables, were surface intensity profile measurements from radial positions of 3 mm, 5 mm, 7 mm, and 9 mm. These locations were selected as a previous depth estimation technique demonstrated success using measurements from these positions [16]. The surface intensity profile measurements, y i , at the i th radial position, were normalized to cancel the effect of optical variation from sample to sample according to:…”

“…Methods of estimating the depth of a light source in tissue have previously involved an inversion of the analytical diffusion model of light propagation [13][14][15]. We have previously shown it is possible to recover source depth using a Monte Carlo-based polynomial model [16]. Our polynomial model produced depth estimates within 2 mm of the true source, down to a depth of 15 mm in tissue-mimicking phantoms.…”