2012 Proceedings - International Tissue Elasticity Conference

Session CVE–2: Cardiovascular Elasticity – II
Friday, October 5 1:30P – 3:00P
017 ACQUISITION OF HIGH FRAME RATE MOVIES OF SIMULTANEOUS ACOUSTIC RADIATION
FORCE IMPULSE (ARFI) AND SHEAR WAVE VELOCITY IMAGES FOR INTRACARDIAC
ECHOCARDIOGRAPHY (ICE) APPLICATIONS IN IN VIVO MYOCARDIUM.
PJ Hollender 1 , SJ Rosenzweig 1 , DP Bradway 1 , R Goswami 2 , PD Wolf 1 , GE Trahey 1 .
1 Duke University, Durham, NC, USA; 2 Duke University Medical Center, Durham, NC, USA.
Background: Imaging the dynamic elastic properties of the heart may be of significant diagnostic
interest, and Acoustic Radiation Force (ARF) imaging methods have been demonstrated as an effective
means of interrogating myocardial elasticity. Intracardiac echocardiography (ICE) transducers provide the
ability to remotely generate and track ARF excitations in myocardium from within the heart. [1,2]
However, conventional imaging sequences for creating ARFI images or Shear Wave Velocity (SWV) images
are prohibitively slow for imaging myocardium through periods of high motion.
Aims: This work demonstrates a method of using customized acquisition sequences, which image the on–axis
(ARFI) and off–axis (SWV) response to excitations with as few as four simultaneously beamformed lines
with ECG triggering to synthesize temporally registered excitation responses through the field of view for
creating series of ARFI and SWV images at a high frame rate.
Methods: Custom beam sequences were written for a phased array ICE transducer for use with Siemens’
Acuson S2000 and SC2000 ultrasound scanners. Parallel beamforming is used to place up to four beams
within the region of excitation and between three and eight beams covering 15 degrees off–axis to one or both
sides. ECG triggering gates fixed frame rate and length (approximately one heartbeat) sequences of excitations
to the cardiac cycle. Successive trigger events modulate the locations of each excitation–tracking ensemble in
the sequence such that, over a number of heartbeats, each azimuthal line in the region of interest is imaged
at each point in the cardiac cycle. The synthesized frame rate and number of azimuthal lines can be increased
by using more beats. The sequences were tested in phantoms and in vivo in a variety of configurations.
Results: Series of images, such as the one shown in Figure 1, were generated, showing good
correspondence between the ARFI images and the SWV images. The images formed movies with up to
17 excitation locations and frame rates up to 200fps. ARFI images showed superior resolution and
performance through periods of high motion, while SWV images showed greater depth uniformity and
provided quantitative estimates of tissue elasticity.
Conclusions: This method was demonstrated to be effective for acquiring series of matched ARFI and
SWV images in in vivo myocardium. Respiration motion was observed to create artifacts in the multi–beat
synthesis of the movies, so holding respiration is important for obtaining quality images. The duration of
breath hold imposes a limit on the number of beats that can be used safely and without artifact. The
achievable frame rate and number of azimuthal locations that can be imaged are, therefore, limited but
sufficient for effectively creating images of the dynamic properties of myocardium.
Acknowledgements: This work is supported by
NIH EB001040, NIH 5R37HL096023 and
NIHR01EB01248.
References:
[1] Hsu et al.: Challenges and Implementation of
Radiation–Force Imaging with an Intracardiac
Ultrasound Transducer. IEEE Trans UFFC, 545,
pp.996–1009, 2007b.
[2] Hollender et al.: Intracardiac Echocardiography
Measurement of Dynamic Myocardial Stiffness with
Shear Wave Velocimetry. Ultrasound in Med. and
Biol., Vol. 38, No. 7, pp. 1271–1283, 2012.
Figure 1: In Vivo Shear Wave Velocity Images and ARFI
Images of porcine Left Ventricular Free Wall
(LVFW). The shear wave speeds are higher in
systole (5m/s) than diastole (2m/s), and the
peak ARFI displacements are correspondingly
lower in systole (11μm) than diastole (18μm).
indicates Presenter 107