Abstract
We show how to apply the Mellin-Laplace transform to process time-resolved reflectance measurements for diffuse optical tomography. We illustrate this method on simulated signals incorporating the main sources of experimental noise and suggest how to fine-tune the method in order to detect the deepest absorbing inclusions and optimize their localization in depth, depending on the dynamic range of the measurement. To finish, we apply this method to measurements acquired with a setup including a femtosecond laser, photomultipliers and a time-correlated single photon counting board. Simulations and experiments are illustrated for a probe featuring the interfiber distance of 1.5 cm and show the potential of time-resolved techniques for imaging absorption contrast in depth with this geometry.
Highlights
Near-infrared optical measurements in biological tissues offer relevant contrast on phenomena related to haemoglobin and other endogenous chromophores like water or lipids
We have developed an original way to take into account the Instrument Response Function (IRF) by using a reference measurement in a known diffusive medium
The analysis and reconstruction results presented in this article were carried out for a given precision of Mellin-Laplace transform (MLT) of p = 3 ns-1, which represents a good compromise between the pieces of information extracted from the Time-Point Spread Functions (TPSFs) and the computation time
Summary
Near-infrared optical measurements in biological tissues offer relevant contrast on phenomena related to haemoglobin and other endogenous chromophores like water or lipids. Detection is the final goal, but in other cases like biopsy guidance, precise localization and quantification of the contrast are the clinically relevant pieces of information. In most cases for human applications, transmission measurements cannot be obtained, so only reflectance measurements are available to retrieve information on optical contrast in depth. Even in cases where transmission measurements could be possible due to anatomy, probe-like configurations enabling only reflectance measurements with small source-detector distances can be preferred. Reflectance-only devices are more portable, facilitating medical practice in applications such as mammography [6] and offer a better control on distances between sources and detectors which is interesting for brain applications, where the use of remote optical fibres in flexible helmets is a cause of localization errors [7]
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