Controlling cavitation-based image contrast in focused ultrasound histotripsy surgery.
OBJECTIVE
To develop MRI feedback for cavitation-based, focused ultrasound, tissue erosion surgery (histotripsy), we investigate image contrast generated by transient cavitation events.


METHODS
Changes in GRE image intensity are observed while balanced pairs of field gradients are varied in the presence of an acoustically driven cavitation event. The amplitude of the acoustic pulse and the timing between a cavitation event and the start of these gradient waveforms are also varied. The magnitudes and phases of the cavitation site are compared with those of control images. An echo-planar sequence is used to evaluate histotripsy lesions in ex vivo tissue.


RESULTS
Cavitation events in water cause localized attenuation when acoustic pulses exceed a pressure threshold. Attenuation increases with increasing gradient amplitude and gradient lobe separation times and is isotropic with gradient direction. This attenuation also depends upon the relative timing between the cavitation event and the start of the balanced gradients. These factors can be used to control the appearance of attenuation while imaging ex vivo tissue.


CONCLUSIONS
By controlling the timing between cavitation events and the imaging gradients, MR images can be made alternately sensitive or insensitive to cavitation. During therapy, these images can be used to isolate contrast generated by cavitation.
Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, USA.
Steven P
SP
Allen
Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, USA.
Timothy L
TL
Hall
Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, USA.
Charles A
CA
Cain
fMRI Laboratory, Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, USA.
Luis
L
Hernandez-Garcia
D000818:Animals; D016477:Artifacts; D057086:High-Intensity Focused Ultrasound Ablation / Q000379:methods*; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D066298:In Vitro Techniques; D008099:Liver / Q000473:pathology* / Q000601:surgery*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013552:Swine; D016896:Treatment Outcome
cavitation; focused ultrasound surgery; histotripsy; intravoxel incoherent motion; tissue erosion; tissue homogenization