Stephanie Eyerly

An in vitro assessment of acoustic radiation force impulse imaging for visualizing cardiac radiofrequency ablation lesions.

Ablation Lesion Quantification with ARFI Imaging. Introduction: Lesion placement and transmurality are critical factors in the success of cardiac transcatheter radiofrequency ablation (RFA) treatments for supraventricular arrhythmias. This study investigated the capabilities of catheter transducer based acoustic radiation force impulse (ARFI) ultrasound imaging for quantifying ablation lesion dimensions.

Intracardiac acoustic radiation force impulse imaging: A novel imaging method for intraprocedural evaluation of radiofrequency ablation lesions

BACKGROUND Arrhythmia recurrence after cardiac radiofrequency ablation (RFA) for atrial fibrillation has been linked to conduction through discontinuous lesion lines. Intraprocedural visualization and corrective ablation of lesion line discontinuities could decrease postprocedure atrial fibrillation recurrence. Intracardiac acoustic radiation force impulse (ARFI) imaging is a new imaging technique that visualizes RFA lesions by mapping the relative elasticity contrast between compliant-unablated and stiff RFA-treated myocardium. OBJECTIVE To determine whether intraprocedure ARFI images can identify RFA-treated myocardium in vivo. METHODS In 8 canines, an electroanatomical mapping-guided intracardiac echo catheter was used to acquire 2-dimensional ARFI images along right atrial ablation lines before and after RFA. ARFI images were acquired during diastole with the myocardium positioned at the ARFI focus (1.5 cm) and parallel to the intracardiac echo transducer for maximal and uniform energy delivery to the tissue. Three reviewers categorized each ARFI image as depicting no lesion, noncontiguous lesion, or contiguous lesion. For comparison, 3 separate reviewers confirmed RFA lesion presence and contiguity on the basis of functional conduction block at the imaging plane location on electroanatomical activation maps. RESULTS Ten percent of ARFI images were discarded because of motion artifacts. Reviewers of the ARFI images detected RFA-treated sites with high sensitivity (95.7%) and specificity (91.5%). Reviewer identification of contiguous lesions had 75.3% specificity and 47.1% sensitivity. CONCLUSIONS Intracardiac ARFI imaging was successful in identifying endocardial RFA treatment when specific imaging conditions were maintained. Further advances in ARFI imaging technology would facilitate a wider range of imaging opportunities for clinical lesion evaluation.

Contrast in Intracardiac Acoustic Radiation Force Impulse Images of Radiofrequency Ablation Lesions

We have previously shown that intracardiac acoustic radiation force impulse (ARFI) imaging visualizes tissue stiffness changes caused by radiofrequency ablation (RFA). The objectives of this in vivo study were to (1) quantify measured ARFI-induced displacements in RFA lesion and unablated myocardium and (2) calculate the lesion contrast (C) and contrast-to-noise ratio (CNR) in two-dimensional ARFI and conventional intracardiac echo images. In eight canine subjects, an ARFI imaging-electroanatomical mapping system was used to map right atrial ablation lesion sites and guide the acquisition of ARFI images at these sites before and after ablation. Readers of the ARFI images identified lesion sites with high sensitivity (90.2%) and specificity (94.3%) and the average measured ARFI-induced displacements were higher at unablated sites (11.23 ± 1.71 µm) than at ablated sites (6.06 ± 0.94 µm). The average lesion C (0.29 ± 0.33) and CNR (1.83 ± 1.75) were significantly higher for ARFI images than for spatially registered conventional B-mode images (C = −0.03 ± 0.28, CNR = 0.74 ± 0.68).

Three-dimensional fusion of Shear Wave Imaging and electro-anatomical mapping for intracardiac radiofrequency ablation monitoring

Electroanatomical Mapping (EAM) provides electrophysiologists with a three-dimensional visualization of endocardial geometry and electrical activity, used to guide transcatheter ablation (TCA) treatment of arrhythmia. Acoustic Radiation Force Impulse (ARFI) and Shear Wave Imaging (SWI) are ultrasonic methods of imaging the mechanical properties of the myocardium that may allow direct visualization of ablation lesion formation, and can be acquired with Intracardiac Echocardiography (ICE) imaging catheters, which are commonly used to guide TCA. The mechanical substrate mapping holds promise to complement the electrical data to improve the safety and efficacy of the procedure. This work demonstrates the use of an image fusion system to stitch a series of in vivo planar ARFI or SWI images together into a 3-D volume of substrate elasticity.

Feasibility of using a generalized-Gaussian Markov random field prior for Bayesian speckle tracking of small displacements

Accurate displacement estimation can be a challenging task in acoustic radiation force elastography, where signal decorrelation can degrade the ability of a normalized cross-correlation (NCC) estimator to characterize the tissue response. In this work, we describe a Bayesian estimation scheme which models both signal decorrelation and thermal noise, and uses an edge-preserving, generalized Gaussian Markov random field prior. The performance of the estimator was evaluated in FEM simulations modeling the acoustic radiation force impulse response in a linearly-isotropic material. Bias, variance, and mean-square error were calculated over a range of estimator parameters, and compared to NCC. The results demonstrate that a significant reduction in mean-square error can be achieved with the proposed estimator. Finally, in vivo data of an radio-frequency ablation in a canine model are shown, demonstrating the in vivo feasibility of the proposed method.

Near real time evaluation of cardiac radiofrequency ablation lesions with intracardiac echocardiography based acoustic radiation force impulse imaging.

[Cardiac radiofrequency (rf) ablation is used to treat cardiac arrhythmias. Multiple rf lesions are created to form lines of electrical block to disrupt arrhythmic wavefronts. However, image based lesion evaluation is not performed and clinicians rely on changes in electrical propagation to evaluate lesion quality. A near real time lesion evaluation system was developed and tested in vitro and in canines using acoustic radiation force impulse imaging (ARFIi) combined with a catheter tracking system (CARTO, Biosense Webster). rf ablation was performed and delivery sites were indicated on a CARTO electroanatomic map. A CARTO spatially tracked SoundStar® catheter was then used to steer the imaging plan to transect lesions, and intracardiac echocardiography (ICE) based ARFIi (Siemens, S2000 Acuson) was used to evaluate lesion contiguity and transmurality. Imaging was gated to diastole when unablated tissue is soft; motion filtering was employed to reduce the effects of catheter and cardiac movement. ARFIi bas...

A comparison of intracardiac ARFI and SWI for imaging radiofrequency ablation lesions

Radiofrequency ablation (RFA) is commonly used to treat cardiac arrhythmias, by generating a contiguous series of discrete radiofrequency ablation (RFA) lesions in the myocardium to destroy or isolate arrhythmogenic conduction pathways. The size of each lesion is controlled by the duration and power of the delivered RF energy, and by the temperature of the tissue at the surface, but feedback on the extent and transmurality of the generated lesion are unavailable with current technology. Intracardiac Echocardiography (ICE) may provide a solution through Acoustic Radiation Force Impulse (ARFI) imaging or Shear Wave Imaging (SWI), which each generate images of local mechanical compliance from very small ultrasonically-induced waves. This work compares ARFI and SWI in an ex vivo experiment for lesion boundary assessment and lesion gap resolution.

Acoustic radiation force impulse imaging of cardiac tissue

Cardiovascular disease remains the most likely cause of death in developed countries, accounting for approximately 870,000 deaths in the United States alone in 2004. Virtually every form of cardiovascular disease involves modifications in tissue stiffness. Acoustic radiation force impulse (ARFI) imaging shows great promise in the regional characterization of tissue stiffness in a variety of clinical applications. Cardiovascular tissues present unique challenges to ARFI imaging because of their dynamic changes in stiffness, high-amplitude physiological motion, and elevated stiffness levels compared to other tissues.

Scanned 3-D Intracardiac ARFI and SWEI for Imaging Radio-Frequency Ablation Lesions

Radio-frequency ablation (RFA) is used to locally disrupt electrical propagation in myocardium and treat arrhythmias, and direct visualization of ablation lesions by acoustic radiation force methods may benefit RFA procedures. This paper compares four imaging modalities, B-mode, acoustic radiation force impulse (ARFI), single-track-location shear wave elasticity imaging (STL-SWEI), and multiple-track-location shear wave elasticity imaging (MTL-SWEI), in their ability to resolve RFA lesions in four ex vivo experiments. Ablation lesions are shown to be marked by at least a local halving of ARFI displacements and doubling of shear wave speeds. In a controlled ablation of ex vivo porcine and canine cardiac tissue, STL-SWEI and ARFI are shown to have a similar CNR, better than MTL-SWEI and B-mode. The SWEI modalities are demonstrated to have improved imaging of distal lesion boundaries. Gaps smaller than 5 mm are visualized in ablation lines made of discretely spaced ablations, and complex structures are reconstructed through depth in an “x” ablation experiment. Scans of suspended atria show increased noise, but successfully visualize ablations in ARFI, MTL-SWEI, and STL-SWEI.

Characterization of catheter motion in intracardiac echocardiography (ICE) elastography imaging

Momentum created by a high intensity acoustic wave emitted in intracardiac echocardiography (ICE) Acoustic Radiation Force Impulse (ARFI) imaging sequences is absorbed by the backing material of the catheter causing a kickback motion. This study was designed to characterize this motion. An elastography phantom was imaged with an 8Fr Soundstar™ ICE catheter and a 10Fr, 128 element ICE catheter with various fulcrum lengths and mechanical steering angles to assess the kickback motion. The fulcrum lengths (FLs) varied from 30 mm to 50 mm and showed irregularities in the motion in FLs over 40 mm in the 8Fr SoundStar™, but not in the 10Fr, 128 element ICE catheter. The mechanical steering, over the range tested in the 8Fr SoundStar™, did not have a statistically significant effect on the kickback motion. The motion was on the same order of magnitude of the induced displacements in both catheters. The kickback motion induces a bias of 0.5 to 3 μm to the ARFI images that is not consistent over the ARFI imaging ensemble. The current motion filtering techniques that are used to remove bulk cardiac or respiratory motion from the induced ARFI displacements are not sufficient for removing the kickback motion. In some cases, the motion filter increases the present bias. For both catheters, failure to properly account for this effect could degrade ICE ARFI image quality. New motion filtering techniques are necessary to reduce the kickback motion effect on induced displacements during ICE ARFI imaging.