Multispectral Optoacoustic Tomography for Functional Imaging in Vascular Research

This protocol using optoacoustic technology enables us to assess a patient's vascular status in real time with functional imaging. And we can explore 3D image scans collected in static or dynamic conditions. The potential interest of such an approach is huge and impacts many health-related fields.

The system provides life in vivo visualization of skin vascular structure at different depths. That means that we can access both skin plexus, the superficial and the deeper, although that requires some repeated experience from the operator With detailed, truly functional imaging, early detection and characterization of microvascular impairment is possible and can be integrated as a diagnostic tool or follow-up protocol to evaluate the progression of disease, and/or effects of treatment. To load subject information, begin by turning on the optoacoustic imaging equipment.

While the equipment is warming up, introduce the Participant Information. The main Welcome window of the software opens to the Scan Overview. Introduce data after clicking on Patient ID, and finish the application by pressing on Select.

Make sure the laser is ready by checking the equipment screen. Following the warm-up time, the laser status bar on the equipment screen must change from laser standby. Select the optoacoustic acquisition preset, hemoglobin, oxyhemoglobin, and melanin, in the examination screen.

Press the laser switch foot pedal and wait for the laser power self-check. After a few seconds, a window appears with the current laser status with a checkup report Release this window by pressing the available OK button. Acclimatize the participant to the laboratory environment, choosing a comfortable position to minimize unnecessary movement.

Ensure that the area to be scanned is previously cleaned. Apply a thin layer of ultrasound gel to the 3D cup. Image stabilization is achieved by holding the 3D cup in the desired imaging position at the volunteer forearm.

After placing the 3D cup on the area of interest, partially lock the stabilizing arm lock for image acquisition. Select the anatomical area for baseline image acquisition. For exploratory purposes, the ventral forearm is recommended.

Apply minimal pressure to the imaging site so that higher pressure readouts can be properly acquired. When the image stability is maximized, capture a snapshot of the area by pressing the Snapshot button on the touchscreen. Acquire the baseline control scan.

To observe the post-occlusive reactive hyperemia maneuver, it's necessary to record a baseline acquisition with the deflated pressure cuff placed in the desired brachial area of the volunteer's arm. After following the previous steps, press and hold the laser foot switch pedal for continuous video acquisition, and pay attention to the View button on the touchscreen. The stabilized image will appear.

Press Record to begin live image recording. Dynamic measurements are required to observe the post-occlusive reactive hyperemia maneuver. Inflate the cuff with suprasystolic pressure, and proceed to acquire images of the vasculature under pressure.

To acquire a video to assess the impact of the pressure release on the imaged vasculature, open the pressure relief valve while acquiring the video. Follow the live image on the screen. Stop the recording by pressing the Stop button.

The optoacoustic imaging platform will stop recording and automatically render the video to Preview mode. In the XY-plane, the melanin signal can be also observed in the planes YZ and XZ, indicating the epidermis limit. The occlusion of the brachial artery provokes some stasis in the larger vessels, visualized by the OT probe.

In consequence, we detected an increase in the overall signals of reduced and oxidized hemoglobin shown as an increase of blue and red colors at axes XY, YZ, and XZ.The melanin signal confirms proper spectral unmixing as it remains constant during post-occlusive reactive hyperemia image acquisition. Unlike the recorded oxyhemoglobin and hemoglobin signals which change with the cuff pressure changes over time. It is critical to handle the 3D probe correctly to obtain good quality images.

Mastering the handling of the probe is crucial for correct data acquisition and analysis. Here, we demonstrate how to use the system under static and dynamic conditions. In this case, we used the post-occlusive reactive hyperemia maneuver, which is a classical challenger to explore local adaptive mechanisms.

We can apply the same strategies with different positionings, measuring in other body sites, and apply other challenges, of course. Established methodologies, such as laser doppler telemetry or photo plethysmography, although very useful, are single point measurements providing limited indiscriminate information partially related with perfusion. The functional information obtained with this system is not comparable from the area of interest to the depth and variables provided.

Measurements here, are made non-invasively in vivo and in real time. The potential for research and diagnostics with clinical application is huge.