Monte Carlo simulations and photoacoustic experiments to compare imaging depth at 532 nm, 800 nm, and 1064 nm

摘要

Photoacoustic imaging (PAI) is a rapidly growing imaging modality which offers the advantages of good optical contrastand high ultrasound resolution. Although PAI provides imaging depth beyond the optical diffusion limit, penetrationdepth in biological samples is limited due to absorption and scattering of light in tissues. Improvement in imaging depthhas been achieved by irradiating the sample with laser pulses of near infrared-I (NIR-I) region (700 nm–900 nm) due todecreased scattering of light in tissues within this optical window. Recently, further improvement in imaging depth hasbeen reported by irradiating the sample in near infrared-II (NIR-II) region (900 nm-1700 nm). In this work, imagingdepth in breast tissues when samples were irradiated by wavelengths in different optical windows has been compared.Initially, Monte Carlo simulation for light propagation in biological tissues was performed to compute imaging depth forexcitation wavelengths of 532 nm, 800 nm, and 1064 nm. Further, photoacoustic tomography at 532 nm, 740 nm, and1064 nm and acoustic resolution photoacoustic microscopy at 570 nm and 1064 nm were conducted to validate theresults. We have shown that maximum imaging depth is achieved by NIR-I (740 nm/ 800 nm) when surface energy forall wavelengths is kept constant. However, when the energy density is proportional to maximum permissible exposure(MPE) at corresponding wavelength, maximum imaging depth is achieved by 1064 nm (NIR-II window). Therefore, weconclude that increased MPE in NIR-II window is responsible for the improved penetration depth in breast tissue in thisregion.