TITLE:
Potential Use of Ultrasonic Cavitation Threshold to Non-Invasively Differentiate Cystic Masses
AUTHORS:
Brian E. O’Neill, Ellen Chang, Nam Yu
KEYWORDS:
Fluid Viscosity, Cavitation Threshold, Mucinous Cyst, Serous Cysts
JOURNAL NAME:
Open Journal of Radiology,
Vol.4 No.4,
December
31,
2014
ABSTRACT: Objectives:
To demonstrate in vitro that changes
in ultrasound cavitation threshold might be used for non-invasively
distinguishing high viscosity mucinous fluid from low viscosity serous fluid in
cystic masses, based on the facts that cavitation threshold increases with
increasing viscosity and that cavitation microbubbles are observable with
diagnostic ultrasound. Methods: An in
vitro model of a cyst was designed using dilutions of ultrasonic gel, and the
cavitation threshold of this model was determined using focused and unfocused
ultrasound for bubble initiation and clinical ultrasound b-scan for detection.
Results: Viscosities of dilutions between 0% and 30% gel were had viscosities
measuring between 1.05 ± 0.08 cP and 6600 ± 875 cP. Inertial cavitation in the
latter was determined to require an order of magnitude greater intensity, at 1
MHz and 100% duty cycle, than the former (>2.2 W/cm2 vs. 2) using unfocused ultrasound. A four-fold increase in the peak
negative pressure was required to initiate significant bubble activity using
1.1 MHz and 50% duty cycle focused ultrasound in the 6600 cP fluid compared with
the 1 cP fluid. Based on these results, it was estimated that a threshold could
be defined that would result in no bubbles in 99.9% of mucinous cysts and just
22% of serous cysts. The remaining 78% of patients presenting with serous cysts
would be positively identified by detection of bubbles, and would be spared an
unnecessary biopsy. Conclusions: The cavitation threshold may be used
non-invasively to distinguish between high viscosity and low viscosity fluids
in cysts and reduce biopsies on serous cysts.