Photoacoustic Imaging for Improved Guidance of Laser Ablation Procedures

 

It is estimated that about 23% of all adults (in US) are at risk for venous insufficiency during their lifetime. Of the estimated 25 million people with symptomatic superficial venous reflux, 1.7 million seek treatment annually. Endovenous laser ablation (EVLA) is a minimally-invasive treatment procedure in which a thin fiber is inserted into the diseased vein.  Light energy generates heat to cauterize the vein internally. Current ultrasound (US)-guided venous ablation procedures often lack precision in tracking the accurate location of the catheter tip inside the vein due to ultrasound imaging artifacts such as angular dependence. Additionally, existing systems lack the ability to determine the thermal dose deposition rate within the tissue.

Photoacoustic (PA) imaging is an emerging imaging technology that allows for ultrasonic detection of light-activated objects. Briefly, in PA, short and low power laser pulses excite the light absorbing chromophores within the tissue (such as red blood cells), causing rapid thermal expansion and the formation of acoustic waves. The omnidirectional PA waves can be received with clinical US transducers, thereby forming PA images. Our system integrates the ultrasound-guided fiber optic ablation technique of EVLA with the PA imaging to enhance the procedure guidance. In particular, our PA system can accurately identify the location of the ablation catheter tip (which is the most important part of the catheter to be accurately visualized) in different clinically-relevant scenarios (such as a straight fiber versus a bent fiber). The nature of the PA signal generation makes the tip visualization independent from all existing US artifacts and false-readings.  Additionally, PA can be easily combined with US to provide a unique image showing the tip of the ablation catheter on top of the background US tissue image. In addition, the generated PA signal varies depending on the temperature of the surrounding tissue. Therefore, the proposed method can accurately measure the thermal dose deposition within the tissue in real time. One key advantage of the proposed technology is the fact that the existing devices can be easily upgraded to use PA with minimal hardware change and low added cost. In addition, the procedure will be easy to adopt by physicians and technicians with an acceptable safety profile. Since the addition of low power pulsed laser does not increase the risk of the procedure, we anticipate that obtaining safety and regulatory approvals for clinical translation will be straightforward.