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Access Type
WSU Access
Date of Award
January 2022
Degree Type
Dissertation
Degree Name
Ph.D.
Department
Biomedical Engineering
First Advisor
Mohammad Mehrmohammadi
Abstract
Image-guided surgeries and therapeutic procedures utilize imaging modalities to enhance the surgeon’s capability of visualizing and guiding the medical instruments within the body. One such application is the endovenous laser ablation (EVLA), which utilizes an ultrasound (US)-guided catheter carrying high power continuous wave (CW) energy for treating varicose veins. Varicose veins, a condition defined by venous insufficiency, affects nearly 40 million people in the United States annually. In EVLA procedures, US limitations including angular dependency, poor contrast-to-noise ratio, poor signal-to-noise ratio, and artifacts limit the ability of the surgeon to detect the catheter tip within the vein. Furthermore, the absence of a real-time temperature feedback system limits the efficacy of EVLA procedures, and can cause various complications, such as deep vein and heat-induced thrombosis, which ultimately leads to the reduced quality of delivered healthcare to patients.To minimize these inaccuracies in image-guided procedures, this PhD dissertation focusses on integrating photoacoustic (PA) imaging into EVLA procedures. A PA-guided laser ablation system was developed by combining the pulsed laser for PA imaging and the CW laser for ablation through dichroic optics into an ablation catheter. Combined US and PA imaging provides simultaneous visualization of background anatomical structures as well as high contrast, artifact-free images of the ablation catheter tip. The ex vivo vessel-mimicking tissue-based phantom studies and in vivo canine studies validated the catheter tracking capability of PA imaging. In addition, PA imaging provides real-time temperature monitoring caused by the CW laser within the vein. Our ex vivo phantom and in vivo canine studies validated the effective thermometry probing capability of PA imaging. However, extreme temperatures in the tissue chromophores result in non-linear changes to the PA amplitude, limiting the accuracy of the thermometry measurements. Hence, the changes in the optical absorption properties of these chromophores were experimentally studied at higher temperatures and the PA-guided thermometry system was calibrated. The calibrated thermometry system provided quantitative temperature measurements which can be further translated in vivo. Moreover, a software-based heat diffusion model was developed and validated, which provided a heatmap at different distances from the heat source during EVLA procedures. These improvements can enhance the physician’s accuracy in performing accurate EVLA procedures and other US-guided procedures, improving treatment outcomes. Additionally, the PA-guided catheter tip tracking and thermometry features have been experimentally validated into other clinical applications including atrial fibrillation and gastrostomy tube placement procedures.
Recommended Citation
John, Samuel, "Photoacoustic Imaging For Image-Guided Interventions" (2022). Wayne State University Dissertations. 3735.
https://digitalcommons.wayne.edu/oa_dissertations/3735