Transcranial imaging with the optoacoustic memory effect

Acoustic mismatched biological tissues such as lungs and bones are known to cause strong distortion and image artifacts when optoacoustic and ultrasound images are rendered by assuming a uniform non-attenuating acoustic medium. Of particular importance is the severe distortion undergone by ultrasound waves as they propagate through the solid skull bone, which generally impedes visualization of cerebral structures in humans with adequate spatial resolution. Optoacoustic image reconstruction by means of model-based inversion has facilitated the development of new approaches potentially capable of correcting for the induced distortion. However, accurate modelling of ultrasound propagation through the skull is challenging due to its highly heterogeneous acoustic and dimensional properties, which result in multiple scattering events, reverberations and mode conversions of the incident longitudinal wave to shear or guided waves. Herein, we demonstrate that the acoustic distortion induced by the skull is preserved for ultrasound waves optoacoustically generated at neighboring point sources. We refer to this phenomenon as the optoacoustic memory effect, which is subsequently exploited for building a three-dimensional optoacoustic model from the collected time-resolved signals corresponding to a light-absorbing particle at a defined position. Model-based inversion based on this approximation is shown to accurately recover the absorption distribution with comparable spatial resolution to that obtained without the presence of the skull.

Automated summary

This study investigates the preservation of acoustic distortion induced by the skull when optoacoustic waves are generated at neighboring point sources, introducing the concept of the "optoacoustic memory effect" for building a three-dimensional optoacoustic model. Model-based inversion using this approximation accurately recovers absorption distribution with comparable spatial resolution to that obtained without the presence of the skull.