Combining two excitation wavelengths for pulsed photothermal profiling of hypervascular lesions in human skin

Abstract

When pulsed photothermal radiometry (PPTR) is used for depth profiling of hypervascular lesions in human skin, melanin absorption also heats the most superficial skin layer (epidermis). Determination of lesion depth may be difficult when it lies close to the epidermal dermal junction, due to PPTR's limited spatial resolution. To overcome this problem, we have developed an approximation technique, which uses two excitation wavelengths (585 and 600 nm) to separate the vascular and epidermal components of the PPTR signal. This technique permits a noninvasive determination of lesion depth and epidermal thickness in vivo, even when the two layers are in close physical proximity to each other. Such information provides the physician with guidance in selecting the optimal parameters for laser therapy on an individual patient basis.

Computational model to evaluate port wine stain depth profiling using pulsed photothermal radiometry

“…In our analysis, reconstructed profiles are presented using a single PPTR signal ͑single wavelength excitation, SWE͒ or PPTR signals obtained using a dual wavelength excitation ͑DWE͒ approach. 25,26 Comparison of the actual and reconstructed profiles from PPTR data revealed a good match. Results of this study indicate that PPTR is a viable approach for depth profiling of PWS skin.…”

“…The PPTR signal ⌬S(t) is considered as the sum of two components, originating from light absorption in blood ͓x(t)͔ and epidermal melanin ͓ y(t)͔. 25 PPTR signals after irradiation at 585 and 600 nm are…”

In vivo results using photothermal tomography for imaging cutaneous blood vessels

“…With appropriate selection of a and 3, according to principles outlined by Majaron et al [12,13], PTT images of epidermal melanin and PWS blood vessels are obtained in separate reconstruction steps. Previous studies [12][13][14] of 1-D depth profiling of PWS skin using this dual wavelength excitation (DWE) approach have demonstrated its advantages over single wavelength excitation (SWE) (e.g.…”

“…Previous studies [12][13][14] of 1-D depth profiling of PWS skin using this dual wavelength excitation (DWE) approach have demonstrated its advantages over single wavelength excitation (SWE) (e.g. , use of 585 nm alone).…”

“…Since the most superficial vessel (255 m depth) was in close proximity to the basal layer, the SWE approach was limited in its ability to differentiate heating of superficial vessels from that of the lower epidermal regions [12]. Use of the DWE approach (Equation 5) allows us to image selectively the vascular component of PWS skin, as evidenced by absence of epidermal heating in the superficial cross section (Figure 5a).…”