Photoacoustic imaging of voltage responses beyond the optical diffusion limit

Area of Science:

• Neuroscience
• Biomedical Engineering
• Optical Imaging

Background:

• Non-invasive optical imaging of neuronal voltage is limited by light scattering in brain tissue.
• Photoacoustic tomography (PAT) uses diffused photons and acoustic detection to overcome optical diffusion limits.
• PAT has not previously been used for voltage response imaging.

Purpose of the Study:

• To demonstrate photoacoustic voltage response imaging in biological samples.
• To overcome the depth limitations of optical imaging for neuronal activity.
• To establish a foundation for future deep brain voltage imaging.

Main Methods:

• Developed spectroscopic photoacoustic tomography (sPAT) using isosbestic wavelengths.
• Applied sPAT to image voltage responses in vitro (HEK-293 cells) and in vivo (mouse brain surface).
• Tested imaging through ex vivo rat brain tissue to demonstrate depth penetration.

Main Results:

• Successfully demonstrated photoacoustic voltage response imaging in cell cultures and on live mouse brain surfaces.
• Utilized sPAT to differentiate voltage signals from hemodynamic signals in vivo.
• Showcased imaging of cell membrane voltage responses through 4.5 mm of brain tissue, exceeding optical diffusion limits.

Conclusions:

• Photoacoustic tomography is a viable method for imaging neuronal voltage responses.
• This technique overcomes the optical diffusion limit, enabling imaging beyond scattering depth.
• While current voltage dyes limit deep in vivo application, the method provides a path for future deep brain studies.