Characterization of cardiovascular liver motion for the eventual application of elasticity imaging to the liverin vivo

Abstract

Elastography, which uses ultrasound to image the tissue strain that results from an applied displacement, can display tumours and heat-ablated tissue with high contrast. However, its application to liver in vivo may be problematic due to the presence of respiratory and cardiovascular sources of displacement. The aim of this study was to measure the cardiovascular-induced component of natural liver motion for the purpose of planning future work that will either use the motion to produce elasticity images or will compensate for it when employing an external source of displacement. A total of 36 sequences of 7 s real-time radio frequency (RF) echo images of the liver were acquired from six healthy volunteers during breath-hold using a stationary 3.5 MHz transducer. For each image sequence, the axial and lateral components of displacement were measured for each pair of consecutive RF images using 2D-echo tracking. The spatio-temporal character of these displacements was then analysed using a novel approach, employing proper orthogonal decomposition, whereby the dominant motion patterns are described by eigenvectors with the highest eigenvalues. The motion patterns of different liver segments were complex, but they were also found to be cyclic, highly repeatable and capable of producing measurable displacements in the liver. These observations provide good evidence to suggest that it may be possible to correct for natural liver motion when using an externally applied displacement for elasticity imaging. It was also found that about 65%-70% of all liver motion could be described using the first eigenvector. Use of only this component of the motion will greatly simplify the design of a mechanical system to be used in an objective study of elasticity imaging of phantoms and excised tissues in the presence of simulated cardiovascular-induced liver motion.

Liver ablation guidance with acoustic radiation force impulse imaging: challenges and opportunities

“…Additionally, the recent implementation of ARFI imaging with parallel receive tracking significantly decreases acquisition times, thus making it easier to complete data acquisition during periods of minimal physiologic motion. Kolen et al (2004) have previously evaluated cardiovascular motion in the liver for applications in elasticity imaging. Similar studies are underway to assess the limitations physiologic motion will impose on ARFI imaging, which has different acquisition protocols than elastography and generally requires individual regions of tissue to be stable for shorter periods of time.…”

A novel motion compensation algorithm for acoustic radiation force elastography

“…These examples were selected, in part, because motion characteristics were of significantly low amplitude such that effects stemming from RF data line decorrelation would not impact analysis of motion filter performance [9]. However, the velocity and acceleration magnitudes used in this study are representative of magnitudes found in vivo [7], [9]. Additionally, the analyses provided have focused upon removing physiological motion in the lateral and axial dimension, and have ignored motion in the elevation (out-of-plane) dimension.…”

“…Motion not associated with these stimuli is generally difficult to relate to local mechanical properties and adds bias and uncertainty to elasticity measurements [7]- [9]. These secondary sources of motion often originate from unwanted transducer movements or from physiological events.…”

Three-Dimensional Electrode Displacement Elastography Using the Siemens C7F2 fourSight Four-Dimensional Ultrasound Transducer

“…This culminates in elastograms with low signal-to-noise (SNRe) and contrast-to-noise (CNRe) ratios. Other disadvantages of external compression elastography in this application include excessive lateral and elevational motion which, when coupled with physiological motion resulting from cardiovascular and respiratory processes, further degrade elastographic image quality (Kolen et al 2002;Varghese et al 2002a;Varghese et al 2002a;Varghese et al 2002b). …”