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Photoacoustic Imaging Could Make Cardiac Interventions Safer

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Researchers at Johns Hopkins University investigated how photoacoustic imaging could be used during cardiac interventions to reduce radiation exposure caused by conventional medical imaging techniques.

In an intervention, a catheter is inserted into a vein or artery, then threaded up to the heart to diagnose and treat heart diseases such as abnormal heartbeats. Doctors typically use fluoroscopy, a sort of x-ray movie that can show only the shadow of the catheter tip and cannot provide detailed information about depth. Fluoroscopy also requires ionizing radiation, which can be harmful to both the patient and the doctor.

The Johns Hopkins researchers tested a combination of photoacoustic imaging and vision-based robotic control. First, they placed an optical fiber inside a catheter’s hollow core, with one end of the fiber connected to a laser to transmit light. They performed cardiac catherization on two live pigs under anesthesia, using fluoroscopy to initially map the catheter’s path on its way to the heart. They used robotic technology to hold the ultrasound probe. Through robotic visual servoing, they were able to automatically track the photoacoustic signal and maintain constant visualization of this signal, receiving image feedback every few millimeters as they guided the catheter through the femoral or jugular vein and toward the heart.

The researchers examined the pigs’ cardiac tissue after the procedures and found no laser-related damage, despite the use of 2.98 mJ per pulse at the fiber tip. While the team needs to perform more experiments to determine whether the robotic photoacoustic imaging system can be miniaturized and used to navigate more complicated pathways, as well as perform clinical trials to definitively prove safety, they say these findings are a promising step forward.

“We envision that ultimately, this technology will be a complete system that serves the fourfold purpose of guiding cardiologists toward the heart, determining their precise locations within the body, confirming contact of catheter tips with heart tissue, and concluding whether damaged hearts have been repaired during cardiac radiofrequency ablation procedures,” professor Muyinatu Bell said.

The researchers believe that this procedure could potentially be applied to any procedure that uses a catheter, such as in vitro fertilization or surgeries using the da Vinci robot, where clinicians need a clearer view of large vessels.

The research was published in IEEE Transactions on Medical Imaging (www.10.1109/TMI.2019.2939568).  

Jul/Aug 2020
photoacoustic imaging
Abbreviated PAI. An imaging modality with a hybrid technique based on the acoustic detection of optical absorption from endogenous chromophores or exogenous contrast agents. Light is absorbed by the chromophores and converted into transient heating, and through thermoelastic expansion there is a resulting emission of ultrasonic waves. In tissue, ultrasound scatters less than light, therefore PAI generates high-resolution images in the diffusive and optical ballistic regimes compared to purely...
optical fiber
A thin filament of drawn or extruded glass or plastic having a central core and a cladding of lower index material to promote total internal reflection (TIR). It may be used singly to transmit pulsed optical signals (communications fiber) or in bundles to transmit light or images.
The study and analysis of images produced by a fluoroscope.
Research & TechnologyeducationAmericasJohns Hopkins Universitybiomedical optical imagingphotoacoustic imagingcatheterizationcardiologymedical roboticsautonomous systemsoptical fiberimaginglight sourcesopticsroboticsfiber laserslasersmedicalBiophotonicsrobotic visual servoingfluoroscopyBioScan

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