Depth determination of chromophores in human skin by pulsed photothermal radiometry

Thomas E Milner,Alice Lau,Derek J Smithies,Dennis M Goodman,J Stuart Nelson

doi:10.1364/ao.35.003379

Abstract

We report on the application of pulsed photothermal radiometry (PPTR) to determine the depth of in-vitro and in-vivo subsurface chromophores in biological materials. Measurements provided by PPTR in combination with a nonnegative constrained conjugate-gradient algorithm are used to determine the initial temperature distribution in a biological material immediately following pulsed laser irradiation. Within the experimental error, chromophore depths (50-450 µm) in 55 in-vitro collagen phantoms determined by PPTR and optical low-coherence reflectometry are equivalent. The depths of port-wine-stain blood vessels determined by PPTR correlate very well with their locations found by computer-assisted microscopic observation of histologic sections. The mean blood-vessel depth deduced from PPTR and histologic observation is statistically indistinguishable (p > 0.94).

Highlights

In recent years, a number of investigators have studied various techniques to image the internal structure of human skin.[1,2,3] Many of these studies have been motivated by efforts to improve diagnosis and treatment of various skin pathologies
Pulsed photothermal radiometry 1PPTR2 is a noncontact technique that utilizes an infrared detector to measure temperature changes induced in a test material exposed to pulsed radiation
Heat generated as a result of light absorption by subsurface chromophores in the test material diffuses to the

Summary

Depth determination of chromophores in human skin by pulsed photothermal radiometry. We report on the application of pulsed photothermal radiometry 1PPTR2 to determine the depth of in-vitro and in-vivo subsurface chromophores in biological materials. Measurements provided by PPTR in combination with a nonnegative constrained conjugate-gradient algorithm are used to determine the initial temperature distribution in a biological material immediately following pulsed laser irradiation. Chromophore depths 150–450 μm[2] in 55 in-vitro collagen phantoms determined by PPTR and optical low-coherence reflectometry are equivalent. The depths of port-wine-stain blood vessels determined by PPTR correlate very well with their locations found by computer-assisted microscopic observation of histologic sections. The mean blood-vessel depth deduced from PPTR and histologic observation is statistically indistinguishable 1 p . The mean blood-vessel depth deduced from PPTR and histologic observation is statistically indistinguishable 1 p . 0.942

Introduction

Methods and Materials

Results and Discussion

For each biopsied skin site a normalized thermal