Effects of the murine skull in optoacoustic brain microscopy

Abstract

Despite the great promise behind the recent introduction of optoacoustic technology into the arsenal of small‐animal neuroimaging methods, a variety of acoustic and light‐related effects introduced by adult murine skull severely compromise the performance of optoacoustics in transcranial imaging. As a result, high‐resolution noninvasive optoacoustic microscopy studies are still limited to a thin layer of pial microvasculature, which can be effectively resolved by tight focusing of the excitation light. We examined a range of distortions introduced by an adult murine skull in transcranial optoacoustic imaging under both acoustically‐ and optically‐determined resolution scenarios. It is shown that strong low‐pass filtering characteristics of the skull may significantly deteriorate the achievable spatial resolution in deep brain imaging where no light focusing is possible. While only brain vasculature with a diameter larger than 60 µm was effectively resolved via transcranial measurements with acoustic resolution, significant improvements are seen through cranial windows and thinned skull experiments.

Prediction and near-field observation of skull-guided acoustic waves

“…From a practical stand-point, the reported skull-guided waves could be potentially used as sole or complementary carriers of acoustic information across the skull in imaging or therapeutic applications. Due to similitudes of the cranial bone structure in small mammals and humans [12], it is generally expected that similar phenomena also exists in human skulls, although must be scaled accordingly in frequency and space. Acoustic scattering and exponential decay along the depth direction (ẑ) may restrict the practical use of the guided-wave phenomenon to low frequencies.…”

Estimation of the skull insertion loss using an optoacoustic point source

“…The signal degradation equally affects optical resolution or acoustic resolution optoacoustic techniques as demonstrated in. 10 …”

Observation of Guided Acoustic Waves in a Human Skull

“…Further experimental and theoretical work is neccesary to fully characterize skull-guided waves, as well as to identify their excitation strategies suitable for in vivo conditions. Observation and characterization of the skull-guided waves can be used for a more accurate interpretation of transcranial image data, such as optoacoustic images that are often afflicted by the complex wave propagation in the skull manifested via distortions in the location and shape of the vascular structures [13]. Our results may thus contribute to the development and optimization of non-invasive ultrasound-based techniques for diagnostic brain imaging [10,[21][22][23]32], monitoring of neural activity [24,25], guided surgery applications [33], or cranial bone assesment without the use of ionizing radiation [18].…”