(G-241) Feasibility of Lesion Assessment with 3D Acoustic Radiation Force Impulse Imaging using Helicoid Array Transducers

This study evaluates the feasibility of using a helicoid array transducer, AcuNav V, for volumetric acoustic radiation force impulse (ARFI) imaging on polyvinyl alcohol cryogel (PVA-C) plate phantoms mimicking homogeneous diastolic atrial myocardium. This technique could potentially improve the clinical endpoint for pulmonary vein isolation (PVI) in atrial fibrillation treatment. This study aims to demonstrate the ability to perform volumetric ARFI and optimize sub-aperture. The results show promise for real-time RF lesion assessment, potentially reducing procedural duration and redo rate in atrial fibrillation treatment.

The AcuNav V system with a helicoid array transducer was used to perform volumetric ARFI imaging on PVA-C plate phantoms mimicking atrial myocardium as shown in Fig. 1. Two homogenous phantoms with different stiffness were created to represent soft and ablated tissue conditions. ARFI imaging was performed using a focused push pulse and track sequences, and ARFI images were generated one millisecond after the push. The volumetric data output was reconstructed using 3D scattered nearest-neighbor interpolation. The push and track sub apertures were varied to observe the effect of these settings.

Table 1 shows that the shear wave group velocities in one and two freeze-thaw cycle phantoms differs, and corresponded to baseline and ablated myocardial tissue, respectively. It also shows that motion-filtered ARFI displacement profiles showed differences between stiffer and softer phantoms. Fig. 2 demonstrates that ARFI displacements increase with the push sub-aperture size up to around 64 elements, after which they decrease due to sidelobes created by the helicoid array's elevation twist. Fig. 3 shows that track sub-apertures with less than 12 elements have lower mean ARFI displacements and higher standard deviations. There is no significant increase in displacement beyond 20 elements.

Different averaged displacements were observed for normal myocardium and ablated tissue. The study also provided insights into sub-aperture size selection.

There exists trade-offs between sub-aperture sizes for push and track sequences, affecting push strength, SNR, and imaging elevation span. Optimal sub-aperture sizes can be identified based on CNR. The AcuNav V may offer potential time reduction for lesion evaluation compared to traditional catheters. PVA phantoms were used for tissue replication, avoiding inconsistencies in ex vivo tissue phantoms.