This paper reports the use of a two-dimensional (2D) capacitive micro-machined ultrasound transducer (CMUT) to acquire radio frequency (RF) echo data from relatively large volumes of a simple ultrasound phantom to compare 3D elasticity imaging methods. Typical 2D motion tracking for elasticity image formation was compared to three different methods of 3D motion tracking, with sum-squared difference (SSD) used as the similarity measure. Differences among the algorithms were the degree to which they tracked elevational motion: not at all (2D search), planar search, combination of multiple planes, and plane independent guided search. The cross correlation between the pre-deformation and motion-compensated post-deformation RF echo fields was used to quantify motion tracking accuracy. The lesion contrast-to-noise ratio was used to quantify image quality. Tracking accuracy and strain image quality generally improved with increased tracking sophistication. When used as input for a 3D modulus reconstruction, high quality 3D displacement estimates yielded accurate and low noise modulus reconstruction.
Abstract. This paper presents a method for registering 3D intracardiac echo (ICE) to pre-operative images. A magnetic tracking sensor is integrated on the ICE catheter tip to provide the 3D location and orientation. The user guides the catheter into the patient heart to acquire a series of ultrasound images covering the anatomy of the heart chambers. An automatic intensity-based registration algorithm is applied to align these ultrasound images with pre-operative images. One of the important applications is to help electrophysiology doctors to treat complicated atrial fibrillation cases. After registration, the doctor can see the position and orientation of the ICE catheter and other tracked catheters inside the heart anatomy in real time. The image guidance provided by this technique may increase the ablation accuracy and reduce the amount of time for the electrophysiology procedures. We show successful image registration results from animal experiments.
Summary. In Electrophysiology catheter ablation is an established treatment for cardiac arrhythmias. Nevertheless, complicated ablation procedures such as Pulmonary vein isolation for atrial fibrillation treatment are difficult to learn. This can be improved by a better integration of the image modalities available today and in the future Electrophysiology lab. In this paper, we present a method to register ultrasound images from an Intracardiac Echo catheter and 3D cardiac C-arm CT images, which can both be obtained during the intervention. This is the first step required to display the Intracardiac Echo images relative to the complex anatomy of the left atrium.
Purpose: Assess the performance of various motion tracking strategies applied to a 3‐D RF echo data set from an oil‐in‐gelatin phantom with spherical targets for a multi‐step deformation totaling about 15% axial strain. Discuss the prospects and preliminary experience of in vivo motion tracking. Method and Materials: A prototype 9‐MHz 2‐D CMUT array connected to a Siemens SONOLINE Antares was used to acquire RF echo data from a 100‐mm × 100‐mm × 70‐mm oil‐in‐gelatin phantom containing a 10‐mm diameter spherical inclusion that has a 5:1 elastic contrast with the background. This CMUT array images like a 1‐D linear array in generating a 2‐D image in the azimuthal plane, and it acquires a 3‐D volume by electronically stepping the 2‐D imaging plane in the elevational direction. A series of controlled compressions of 1.5–2% axial strain were applied. Phantom motion was tracked with off‐line data processing using different approaches including 2‐D, 2.5‐D and 3‐D axial guidance tracking. The method that performed the best was applied to a 3‐D in vivo data set obtained with the same transducer. Results: The contrast to noise ratios (CNR) and the cross correlation between the motion‐compensated RF and the reference RF for the four motion tracking approaches were used as metrics of performance. The CNR increased with increasingly sophisticated motion tracking with 3‐D axial guidance performing the best. The same trend was observed with the normalized cross correlation. Tracking in vivo data has proved more difficult. Conclusions: These results demonstrate the improvement in motion tracking available through 3‐D tracking. This work also demonstrates that volume data acquisition allows accurate motion tracking and axial strain image formation for an entire target (within the field of view). Volume data acquisition with 2‐D arrays will provide a major advancement in the capabilities of elasticity imaging systems.
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