Photoacoustic Monitoring of Dye Movement in Cortical Blood Vessels

Place an anesthetized rat, pre-applied with ultrasound gel, on a lab jack at the center of a scanner with ultrasound transducers.

Activate the pulsed laser diode within the scanner to emit light pulses.

Blood components in the brain's blood vessels, including the sinus, absorb these pulses, causing localized heating, vessel expansion, and generating photoacoustic signal waves.

The transducers rotate fully to detect these signals, creating cross-sectional images of the brain’s vessels.

Stop the laser and adjust the scanner for partial transducer rotation to collect baseline data.

Inject an imaging dye intravenously into the rat's tail.

During the wash-in, the dye spreads through the brain’s blood vessel and binds to plasma proteins.

Scanning detects enhanced pulse absorption, producing strong photoacoustic signals.

During the wash-out, the dye is metabolically cleared, reducing the signal strength.

Generate the vasculature image and obtain the photoacoustic signals to visualize dye absorption and clearance, providing insights into blood flow in the brain.

After setting the parameters in the data acquisition software for a 360-degree acquisition scan, enable the output of the function generator to turn on the pulsed laser diode laser emission. Slowly increase the voltage of the variable high voltage power supply to 120 volts for maximum per pulse energy.

Run the data acquisition software program to rotate all eight of the transducers 360 degrees over a four-second scan time. Disable the output of the function generator to turn off the laser emission. Using the reconstruction algorithm in the data processing software, determine the scanning radius of all eight of the transducers by trial and error using the backprojection algorithm.

Set the parameters in the data acquisition software for a 45-degree acquisition over a 0.5 second scan time. Enable the output of the function generator to turn on the laser emission. Run the data acquisition software program to rotate all eight of the transducers 45 degrees to obtain the initial control data. Disable the output of the function generator to turn off the laser emission.

Next, inject 0.3 milliliters of indocyanine green into the tail vein of the rat. Enable the output of the function generator to turn on the laser emission. Then run the data acquisition software to acquire A-lines over a 0.5-second scan time in a 45-degree rotation. At the end of the acquisition, use the backprojection algorithm to reconstruct the cross-sectional brain image from the saved A-lines.