Large-Scale Single-Cell Photoacoustic Microscopy of the Brain in Action

The brain accounts for more than 20% of total oxygen consumption even at the resting state. Oxygen metabolism is not only closely associated with neuron activities, but also plays a key role in many life-threatening brain disorders, such as ischemic stroke, Alzheimer’s disease, seizure, neurodegeneration, and brain tumors. In vivo imaging of cerebral oxygen delivery in small-animal disease models is of crucial importance for understanding pathogenic mechanisms and exploring new therapeutic strategies in translational medicine. Because of the highly dynamic nature and close interconnections among different sub-regions in the brain, imaging of cerebral oxygen delivery does not only require high spatial resolution, but also needs to achieve high imaging speed over a large field of view. However, it is still challenging for existing biomedical imaging techniques to meet all of these requirements in a single imaging modality.In 2013, the PI demonstrated that voice-coil photoacoustic microscopy can quantitatively image oxygen release from single red blood cells in a capillary, which sheds light on functional brain imaging with an unprecedented single-cell resolution. Here we propose a major technical advance based on voice-coil photoacoustic microscopy that can image oxygen release from single red blood cells in large-scale vessels in the brain. The proposed project will build a new photoacoustic microscope based on an ultrafast scanning mirror and a voice-coil stage to achieve video-rate three-dimensional imaging over a large field of view. A dual-pulse-width method will be used to determine the oxygen saturation in each flowing red blood cells with 800-kHz pulse repetition rate.This novel brain imaging capability enables monitoring oxygen delivery with the ultimate single-cell resolution and a large field of view. This allows us study the interconnections among different sub-regions in the brain cortex with single-cell resolution. In addition, we can simultaneously quantify multiple important state parameters, such as total hemoglobin concentration, blood oxygen saturation, and blood flow speed, in multiple capillaries and trunk vessels. These state parameters can provide insights into the mechanisms behind the oxygen supply changes in the brain. The in vivo imaging of oxygen delivery at the single-cell resolution in large-scale blood vessels represents a powerful enabling technique for functional imaging—potentially opening up many new applications in preclinical brain imaging, such as studying coupling between neuron activities and single-cell oxygen release in a large area, or monitoring the progress and therapeutic outcomes of ischemic stroke, Alzheimer’s disease, or glioblastoma.