Report Submission Date:
Section 1: Projects you are the lead
3D Functional Photoacoustic Imaging of Mouse Brain with Multispectral Windowing Using High Frequency Linear Ultrasound Probe
In recent years, advanced imaging methodologies with increased spatial and temporal resolution have been used to extend our understanding of brain functions. Brain positron emission tomography (PET) is a metabolic imaging method that detects the emissions from radioactive tracers that are injected into the blood stream and eventually reach the brain . Functional magnetic resonance imaging (fMRI) measures brain activity by using the blood oxygenation level-dependent (BOLD) effect .
Both methods have drawbacks: PET uses ionizing radiation and has poor spatial resolution, and fMRI is too slow for studying fast hemodynamics. Recently, functional ultrasound imaging has successfully been used to monitor cerebral microvascular hemodynamics deep in the rat brain with high spatiotemporal resolution [3, 4]. Optical imaging techniques, such as optical coherence tomography and multiphoton microscopy, have also been demonstrated for imaging neural activity with cellular and subcellular resolution [5, 6], but the shallow penetration limits their observation to only the cortical layer (~1–2 mm). Given these limitations, photoacoustic (PA) Imaging (PAI) can play a complementary role.
Section 2: Projects you are collaborating
Internal Structure of Mouse Brain:
There were eight main regions reconstructed in the atlas. These regions include the olfactory bulb, limbic, parietal, somatosensory, retrosplenial, visual, motor, and temporal regions. Also, several subregions within the main regions were reconstructed in the atlas .
In this study, we utilize photoacoustic imaging system to image the mouse brain and to investigate the effect of different wavelength of the laser pulse on different part of the brain using spectral windowing. The experiment was performed using ultrasound probe from Verasonics (L38-V22) and Laser system from Opotek (Phocus). The laser and the ultrasound probe were connected to a custom-made holder and the laser illuminate from the side of the ultrasound probe. We have applied different wavelength to find the effect on different regions of the brain using the spectral windowing of the received signals.
Section 3: Manuscript
Need to know the Numerical Aperture of Optical fiber and the manufacturer details
The diagram of the photoacoustic imaging system is shown in figure 1. A Q‐switched Nd:Yag Opotek Phocus HE MOBILE laser (OPOTEK, LLC) with the pulse width of 5 ns and the repetition rate of 10 Hz was used. The laser was tuned using an internal optical parametric oscillator (OPO). The laser energy was controlled with an internal attenuator. A 12-bundle optical fiber with 0.75mm diameter each and the bundle diameter is 4.5mm was coupled with the laser using the 3D printed adapter at the Laser end and another end is custom printed holder of the transducer probe. For PA signal detection, an L38-22v capacitive micromachined ultrasonic transducer (CMUT) High Frequency Linear Array (Kolo SiliconWave) ultrasound probe with 256‐elements and 30-MHz central frequency was used (elevation focus: 8mm; aperture: 1.8 mm). Both the optical fibers and the probe were attached to a 3D XYZ motorized stage (Optics Focus- MOXYZ-02-100-100-100). The stage is controlled by a computer software and the stage is connected using a USB cable. The data were taken at a precision step of 0.6µ through the entire scanning area. Several wavelengths of pulse laser from 690-950nm were triggered. PA signal acquisition was performed using a 128‐channel, high‐frequency, programmable ultrasound system (Vantage 128, Verasonics Inc.). Both the data acquisition (DAQ) system and the laser flash lamp were triggered using a 10 Hz square pulse train at 5 V peak‐peak generated by a function generator. The Q‐switch was triggered by the Vantage 128. All the procedures were controlled through a MATLAB graphical user interface.
Manuscript In Preparation
The in-vivo study is BRL at University of Illinois (Chicago) approved. Description of what kind of mouse, weight, age, how many? Explain how the scalp is removed. What is anesthetic procedure and parameters set initially and during the experiment?
Section 4: Ideas
Ideas that worth perusing
The scalp of the mouse was surgically removed, and the exposed skull was cleaned with 0.9% sodium chloride irrigation solution right before imaging. Ultrasonic gel was used for ultrasound coupling and maintaining skull hydration. BL6 Mice were (X weeks old) used for this experiment. The mouse was obtained from Lab, UIC.