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Biomedical Optics Express

Biomedical Optics Express

  • Editor: Joseph A. Izatt
  • Vol. 4, Iss. 3 — Mar. 1, 2013
  • pp: 447–459

Improving the depth sensitivity of time-resolved measurements by extracting the distribution of times-of-flight

Mamadou Diop and Keith St. Lawrence  »View Author Affiliations

Biomedical Optics Express, Vol. 4, Issue 3, pp. 447-459 (2013)

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Time-resolved (TR) techniques provide a means of discriminating photons based on their time-of-flight. Since early arriving photons have a lower probability of probing deeper tissue than photons with long time-of-flight, time-windowing has been suggested as a method for improving depth sensitivity. However, TR measurements also contain instrument contributions (instrument-response-function, IRF), which cause temporal broadening of the measured temporal point-spread function (TPSF) compared to the true distribution of times-of-flight (DTOF). The purpose of this study was to investigate the influence of the IRF on the depth sensitivity of TR measurements. TPSFs were acquired on homogeneous and two-layer tissue-mimicking phantoms with varying optical properties. The measured IRF and TPSFs were deconvolved using a stable algorithm to recover the DTOFs. The microscopic Beer-Lambert law was applied to the TPSFs and DTOFs to obtain depth-resolved absorption changes. In contrast to the DTOF, the latest part of the TPSF was not the most sensitive to absorption changes in the lower layer, which was confirmed by computer simulations. The improved depth sensitivity of the DTOF was illustrated in a pig model of the adult human head. Specifically, it was shown that dynamic absorption changes obtained from the late part of the DTOFs recovered from TPSFs acquired by probes positioned on the scalp were similar to absorption changes measured directly on the brain. These results collectively demonstrate that this method improves the depth sensitivity of TR measurements by removing the effects of the IRF.

© 2013 OSA

OCIS Codes
(170.3660) Medical optics and biotechnology : Light propagation in tissues
(170.3890) Medical optics and biotechnology : Medical optics instrumentation

ToC Category:
Optics of Tissue and Turbid Media

Original Manuscript: November 13, 2012
Revised Manuscript: January 24, 2013
Manuscript Accepted: February 13, 2013
Published: February 15, 2013

Mamadou Diop and Keith St. Lawrence, "Improving the depth sensitivity of time-resolved measurements by extracting the distribution of times-of-flight," Biomed. Opt. Express 4, 447-459 (2013)

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