Abstract
Successful laser treatment of port wine stain (PWS) birthmarks requires knowledge of lesion geometry. Laser parameters, such as pulse duration, wavelength, and radiant exposure, and other treatment parameters, such as cryogen spurt duration, need to be optimized according to epidermal melanin content and lesion depth. We designed, constructed, and clinically tested a photoacoustic probe for PWS depth determination. Energy from a frequency-doubled, Nd:YAG laser (lambda=532 nm, tau(p)=4 nanoseconds) was coupled into two 1,500 mum optical fibers fitted into an acrylic handpiece containing a piezoelectric acoustic detector. Laser light induced photoacoustic waves in tissue phantoms and a patient's PWS. The photoacoustic propagation time was used to calculate the depth of the embedded absorbers and PWS lesion. Calculated chromophore depths in tissue phantoms were within 10% of the actual depths of the phantoms. PWS depths were calculated as the sum of the epidermal thickness, determined by optical coherence tomography (OCT), and the epidermal-to-PWS thickness, determined photoacoustically. PWS depths were all in the range of 310-570 microm. The experimentally determined PWS depths were within 20% of those measured by optical Doppler tomography (ODT). PWS lesion depth can be determined by a photoacoustic method that utilizes acoustic propagation time.
Highlights
Photoacoustics in biomedical optics may be described as a laser induced ultrasound
The photoacoustic signals and optical coherence tomography (OCT) and optical Doppler tomography (ODT) images for the dorsal hand, dorsal ring ®nger, palm, and palmar ring ®nger port wine stain (PWS) are shown in Figures 6±9, respectively
The probe was tested on PWS skin with successful acoustic wave detection and subsequent analysis leading to lesion depth determination
Summary
Photoacoustics in biomedical optics may be described as a laser induced ultrasound. while conventional ultrasound detects interfaces of different acoustic impedances, laser light in photoacoustics is transduced into acoustic energy so that the region of interest becomes an active source. Viator et al [3] determined the thickness of a turbid gel over an absorbing layer as a model of necrotic tissue over normally perfused tissue after photodynamic therapy. The latter application can be adapted to the problem of port wine stain (PWS) depth determination, which would aid in the treatment of these lesions. Successful laser treatment of port wine stain (PWS) birthmarks requires knowledge of lesion geometry. The photoacoustic propagation time was used to calculate the depth of the embedded absorbers and PWS lesion. Conclusions: PWS lesion depth can be determined by a photoacoustic method that utilizes acoustic propagation time.
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