Impacts of the murine skull on high‐frequency transcranial photoacoustic brain imaging

Abstract

Non‐invasive photoacoustic tomography (PAT) of mouse brains with intact skulls has been a challenge due to the skull's strong acoustic attenuation, aberration, and reverberation, especially in the high‐frequency range (>15 MHz). In this paper, we systematically investigated the impacts of the murine skull on the photoacoustic wave propagation and on the PAT image reconstruction. We studied the photoacoustic acoustic wave aberration due to the acoustic impedance mismatch at the skull boundaries and the mode conversion between the longitudinal wave and shear wave. The wave's reverberation within the skull was investigated for both longitudinal and shear modes. In the inverse process, we reconstructed the transcranial photoacoustic computed tomography (PACT) and photoacoustic microscopy (PAM) images of a point target enclosed by the mouse skull, showing the skull's different impacts on both modalities. Finally, we experimentally validated the simulations by imaging an in vitro mouse skull phantom using representative transcranial PAM and PACT systems. The experimental results agreed well with the simulations and confirmed the accuracy of our forward and inverse models. We expect that our results will provide better understanding of the impacts of the murine skull on transcranial photoacoustic brain imaging and pave the ways for future technical improvements.

A Skull-Removed Chronic Cranial Window for Ultrasound and Photoacoustic Imaging of the Rodent Brain

“…The cross-sectional profiles of four selected vessels (azPA, RRV, AchA, and LSCA) are co-plotted with their corresponding control group in different line types (Figure 4D). Obviously, the vessel signal of the skull-removed mouse was about four times stronger than that of the normal mouse, which is consistent with an earlier theoretical prediction (Liang et al, 2019).…”

“…Kneipp et al, estimated the skull insertion loss using a photoacoustic point source and found good quantitative agreement between their model and measurements (Oraevsky et al, 2016). Yao et al (2015) investigated the evolution of the acoustic waveform when penetrating through the skull (Liang et al, 2019). Acoustic ray-tracing was used to calculate the phase distortion along the acoustic travel path, and compensation algorithms were developed based on vector space similarity model and ray-tracing simulations (Mohammadi et al, 2020).…”

Recent Technical Progression in Photoacoustic Imaging—Towards Using Contrast Agents and Multimodal Techniques

“…These disadvantages complicate accurate image reconstruction. Yao's group systematically investigated the impact of murine skull on PA wave propagation and the corresponding PAI image reconstruction [83]. Their results confirmed that transcranial PACT displayed an inferior image quality compared with transcranial PAM (seen Figure 5), even in instances where the two modalities use a similar US frequency and effective detection aperture.…”

Multimodal Contrast Agents for Optoacoustic Brain Imaging in Small Animals

“…In the NIR I range, light scattering, hemoglobin absorbance, and skull attenuation interferes in the signal/noise ratio, unmixing, and penetration depth in the small animal brain ( Wan et al, 2018 ; Liang et al, 2019 ). The skull attenuation positively associates with increasing age, which makes imaging in aged disease animal models difficult.…”