Impact of skin tone on target size detectability in photoacoustic breast imaging.

Significance: Photoacoustic imaging has the potential to improve non-invasive breast cancer diagnosis. However, illumination through the skin introduces a skin tone bias, as greater melanin content increases optical absorption and can create acoustic clutter, reducing the visibility of various target sizes.

Aim: We investigate the impact of skin tone bias as a function of target sizes in three photoacoustic image reconstruction methods: fast Fourier transform (FFT)-based reconstruction, delay-and-sum (DAS) beamforming, and short-lag spatial coherence (SLSC) beamforming.

Methods: The three imaging methods were applied to channel data from multidomain simulations with 757, 800, and 1064 nm wavelengths, 11 target sizes (ranging 0.5 to 3 mm), 18 skin tones [ranging individual typology angles (ITAs) of -54 deg to 60 deg], and a previously validated realistic 3D breast model. The signal-to-noise ratio (SNR) and generalized contrast-to-noise ratio (gCNR) were measured to assess visibility.

Results: With 757 and 800 nm wavelengths, targets underlying dark skin tones (ITA range: -54 deg to -33 deg) with sizes ≤3 mm were poorly visible with ≤2.38 to 4.21 mean SNR and ≤0.46 to 0.74 mean gCNR, with smaller targets generally being more visible with lighter skin tones. A 1064-nm transmit wavelength improved visualization with DAS and SLSC beamforming, relative to both FFT reconstruction with a 1064 nm wavelength and DAS or SLSC beamforming with 757 and 800 nm wavelengths. When combined with SLSC beamforming, the 1064-nm wavelength offered the greatest improvements, enabling visualization of simulated target sizes ranging from 0.5 to 3 mm underlying very light (ITA = 60 deg) to dark (ITA = -54 deg) skin tones, with mean SNR ≤10.01 and mean gCNR ≤1. Visualization of simulated vessel structures derived from in vivo photoacoustic images was consistent with simulation-based target size expectations.

Conclusions: Results are promising for advancing next-generation photoacoustic imaging systems for breast cancer diagnosis across the range of skin tones represented in healthcare systems throughout the world.