Title :
Imaging feedback for histotripsy by characterizing dynamics of acoustic radiation force impulse (ARFI)-induced shear waves excited in a treated volume
Author :
Tzu-Yin Wang ; Hall, T. ; Zhen Xu ; Fowlkes, J. ; Cain, Charles
Author_Institution :
Dept. of Radiol., Stanford Univ., Palo Alto, CA, USA
Abstract :
Our previous study indicated that shear waves decay and propagate at a lower speed as they propagate into a tissue volume mechanically fractionated by histotripsy. In this paper, we hypothesize that the change in the shear dynamics is related to the degree of tissue fractionation, and can be used to predict histotripsy treatment outcomes. To test this hypothesis, lesions with different degrees of tissue fractionation were created in agar-graphite tissue phantoms and ex vivo kidneys with increasing numbers of therapy pulses, from 0 to 2000 pulses per treatment location. The therapy pulses were 3-cycle 750-kHz focused ultrasound delivered at a peak negative/positive pressure of 17/108 MPa and a repetition rate of 50 Hz. The shear waves were excited by acoustic radiation force impulse (ARFI) focused at the center of the lesion. The spatial and temporal behavior of the propagating shear waves was measured with ultrasound plane wave imaging. The temporal displacement profile at a lateral location 10 mm offset to the shear excitation region was detected with M-mode imaging. The decay and delay of the shear waves were quantitatively characterized on the temporal displacement profile. Results showed significant changes in two characteristics on the temporal displacement profile: the peak-to-peak displacement decayed exponentially with increasing numbers of therapy pulses; the relative time-to-peak displacement increased with increasing numbers of therapy pulses, and appeared to saturate at higher numbers of pulses. Correspondingly, the degree of tissues fractionation, as indicated by the percentage of structurally intact cell nuclei, decreased exponentially with increasing numbers of therapy pulses. Strong linear correlations were found between the two characteristics and the degree of tissue fractionation. These results suggest that the characteristics of the shear temporal displacement profile may provide useful feedback information regarding the treatment outcomes.
Keywords :
biological effects of acoustic radiation; biomechanics; cavitation; elastic waves; phantoms; radiation pressure; ultrasonic imaging; ultrasonic therapy; ARFI induced shear waves; M-mode imaging; acoustic radiation force impulse; agar-graphite tissue phantoms; ex vivo kidneys; focused ultrasound; frequency 750 kHz; histotripsy imaging feedback; mechanically fractionated tissue volume; peak negative pressure; peak positive pressure; pressure 108 MPa; pressure 17 MPa; propagating shear wave spatial behavior; propagating shear wave temporal behavior; relative time to peak displacement; shear dynamics; shear excitation region; shear wave decay; shear wave propagation; structurally intact cell nuclei; temporal displacement profile; therapy pulse; tissue fractionation degree; ultrasound plane wave imaging; Fractionation; Imaging; Kidney; Lesions; Medical treatment; Ultrasonic imaging; Ultrasonic variables measurement;
Journal_Title :
Ultrasonics, Ferroelectrics, and Frequency Control, IEEE Transactions on
DOI :
10.1109/TUFFC.2014.3013