Volumetric Acoustic Radiation Force Impulse Imaging Using Intracardiac Echocardiography
Intracardiac echocardiography (ICE) based elastography methods have the potential to be useful for a number of clinical purposes including monitoring of ablation lesion formation and myocardial substrate characterization. However, 2-D field-of-view ICE catheters currently in use in the clinic have difficulties imaging face-on regions of myocardial tissue, requiring meticulous and time-consuming translational and rotational scanning of the array. This dissertation investigates the use of helicoid array transducers to perform ICE-based acoustic radiation force impulse (ARFI) imaging on multiple elevation planes at once, improving on current methods in terms of speed and ease-of-use.
The Siemens Acuson SC2000 ultrasound scanner was programmed with sequences to perform SWEI imaging on the Soundstar 8F linear array ICE catheter and to perform volumetric ARFI scans using the AcuNav V helicoid array catheter. These sequences were used respectively to characterize the stiffness contrast in ablated human atrial tissue and to characterize the performance of volumetric ARFI at detecting gaps in atrial tissue phantoms.
The first research chapter is a clinical study showing that shear wave elastography (SWE) using a traditional 2-D field-of-view ICE catheter can be used to distinguish between baseline and ablated left atrial (LA) tissue in patients undergoing radiofrequency ablation (RFA) for atrial fibrillation (AF). Shear wave velocities of baseline LA and right atrium (RA), low electrogram voltage areas of the LA, and ablated LA are reported. The second chapter investigates through simulation and experiments the volumetric B-mode imaging performance of helicoid array transducers. Experimental verification of pressure field simulations is done by the use of the Siemens Acuson AcuNav V, a 128-element helicoid array transducer. Guided by these results, a discussion of the design of helicoid array transducer imaging sequences is presented. The final chapter is about the use of the helicoid array transducer for volumetric ARFI imaging. Experiments in tissue phantoms of varying elasticities and inclusions demonstrate that it is possible to identify gaps as narrow as 1 mm when the contrast is similar to that of baseline and ablated human LA myocardium.
This work demonstrates the feasibility of using helicoid array transducers for volumetric elastography imaging of the heart and establishes a foundation for future clinical investigations using this technology.
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