Impact of skin pigmentation on photoacoustic imaging using linear array transducer: a pilot in vivo study

Clinical photoacoustic (PA) imaging systems commonly integrate illumination and detection into the same probe. In this case, PA waves originating from light absorption by melanin in the skin propagate into the tissue and are backscattered to the transducer, which introduces acoustic clutter artifacts. In addition, skin absorption also decreases light fluence within the imaging plane. Therefore, it is important to understand how the amount of melanin in the epidermis impacts PA imaging quality. Toward this goal, PA images of 10 volunteers with different skin constitutive pigmentation were acquired with laser wavelengths of 750 nm, 810 nm, and 870 nm. The radial artery was adopted as the reference to calculate signal-to-noise ratios (SNRs) in order to quantify the presence of clutter artifacts in conventional amplitude-based PA images, as well as the capability of reducing clutter by applying short-lag spatial coherence (SLSC) beamforming. With conventional amplitude-based beamforming, the mean SNR across the 10 volunteers decreased from 38.9 dB to 33.7 dB with the decreasing epidermal melanin content. However, the mean SNR improved by 4.2 dB with SLSC PA images compared to conventional PA images. Overall, SLSC beamforming successfully reduced the appearance of clutter artifacts in PA images, resulting in better visualization of the radial artery and improved image quality. These results are promising to implement SLSC to both reduce acoustic clutter and improve target visualization in photoacoustic images acquired with light transmission through darker skin tones.