Label-free photoacoustic tomography of whole mouse brain structures ex vivo

Abstract

Abstract. Capitalizing on endogenous hemoglobin contrast, photoacoustic-computed tomography (PACT), a deep-tissue high-resolution imaging modality, has drawn increasing interest in neuroimaging. However, most existing studies are limited to functional imaging on the cortical surface and the deep brain structural imaging capability of PACT has never been demonstrated. Here, we explicitly studied the limiting factors of deep brain PACT imaging. We found that the skull distorted the acoustic signal and blood suppressed the structural contrast from other chromophores. When the two effects are mitigated, PACT can potentially provide high-resolution label-free imaging of structures in the entire mouse brain. With 100-μm in-plane resolution, we can clearly identify major structures of the brain, which complements magnetic resonance microscopy for imaging small-animal brain structures. Spectral PACT studies indicate that structural contrasts mainly originate from cytochrome distribution and that the presence of lipid sharpens the image contrast; brain histology results provide further validation. The feasibility of imaging the structure of the brain in vivo is also discussed. Our results demonstrate that PACT is a promising modality for both structural and functional brain imaging.

Uniform light delivery in volumetric optoacoustic tomography

“…The laser was tuned to a wavelength of 532 nm for sphere phantom imaging, a highly absorbing wavelength for blood and commonly used for phantom testing in OA tomography . Excitation wavelength of 590 nm was used for both heart and brain imaging, as it has been previously shown to attain high contrast for elucidating organ structures . The laser was operated at a pulse repetition frequency of 10 Hz.…”

Real-time spectroscopic photoacoustic/ultrasound (PAUS) scanning with simultaneous fluence compensation and motion correction for quantitative molecular imaging

“…PA tomography (PAT) and microscopy (PAM) have numerous diagnostic applications [9][10][11], providing both endogenous [12][13][14][15] and exogenous molecular contrast in structural and functional images [15][16][17]. In particular, PA spectroscopy has produced functional images in the brain and heart [10,[18][19][20], and molecular images using the unique spectra of nanoengineered contrast agents [16,[20][21][22]. These tools have been extended to clinical breast cancer screening [23][24][25][26], skin lesion diagnosis [27,28], biopsy guidance [29,30], gastrointestinal imaging [31], and tumor metastases and lymph node screening [32].…”

Dichroism-sensitive photoacoustic computed tomography

“…PA computed tomography (PACT) is an embodiment of PAT that provides up to multiple centimeters' imaging depth in tissues with high spatial resolution [8][9][10][11]. Here, we present a new approach, called dichroism-sensitive PACT (DS-PACT), which we developed by upgrading a conventional PACT system [12] for dichroism measurement.…”