The efficacy of using subharmonic emissions from Sonazoid microbubbles (GE Healthcare, Oslo, Norway) to track portal vein pressures and pressure changes was investigated in 14 canines using either slow- or high-flow models of portal hypertension (PH). A modified Logiq 9 scanner (GE Healthcare, Milwaukee, WI) operating in subharmonic mode (ftransmit:2.5MHz, freceive:1.25MHz) was used to collect RF data at 10-40% incident acoustic power levels with 2-4 transmit cycles (in triplicate), before and after inducing PH. A pressure catheter (Millar Instruments, Inc., Houston, TX) provided reference portal vein pressures. At optimum insonification, subharmonic signal amplitude changes correlated with portal vein pressure changes; r ranged from -0.82 to -0.94 and from -0.70 to -0.73 for PH models considered separately or together, respectively. The subharmonic signal amplitudes correlated with absolute portal vein pressures (r: -0.71 to -0.79). Statistically significant differences between subharmonic amplitudes, before and after inducing PH, were noted (p≤0.01). Portal vein pressures estimated using SHAPE did not reveal significant differences (p>0.05) with respect to the pressures obtained using the Millar pressure catheter. Subharmonic aided pressure estimation may be useful clinically for portal vein pressure monitoring.
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