Noninvasive estimation of dynamic pressures in vitro and in vivo using the subharmonic response from microbubbles

Abstract

The purpose of this study was to develop and validate a noninvasive pressure estimation technique based on subharmonic emissions from a commercially available ultrasound contrast agent and scanner, unlike other studies that have either adopted a single-element transducer approach and/ or use of in-house contrast agents. Ambient pressures were varied in a closed-loop flow system between 0 and 120 mmHg and were recorded by a solid-state pressure catheter as the reference standard. Simultaneously, the ultrasound scanner was operated in pulse inversion mode transmitting at 2.5 MHz, and the unprocessed RF data were captured at different incident acoustic pressures (from 76 to 897 kPa). The subharmonic data for each pulse were extracted using band-pass filtering with averaging, and subsequently processed to eliminate noise. The incident acoustic pressure most sensitive to ambient pressure fluctuations was determined, and then the ambient pressure was tracked over 20 s. In vivo validation of this technique was performed in the left ventricle (LV) of 2 canines. In vitro, the subharmonic signal could track ambient pressure values with r(2) = 0.922 (p < 0.001), whereas in vivo, the subharmonic signal tracked the LV pressures with r(2) > 0.790 (p < 0.001) showing a maximum error of 2.84 mmHg compared with the reference standard. In conclusion, a subharmonic ultrasound-based pressure estimation technique, which can accurately track left ventricular pressures, has been established.

Chronic Liver Disease: Noninvasive Subharmonic Aided Pressure Estimation of Hepatic Venous Pressure Gradient

“…Since its implementation on two modified commercial US scanners, SHAPE has been used to track dynamic pressures in vitro (12), to monitor interstitial fluid pressures in a swine melanoma model (13), and to separately measure left ventricular pressures and changes in portal pressures in canine models (14,15).…”

Processing of Subharmonic Signals from Ultrasound Contrast Agents to Determine Ambient Pressures

“…A 2.5 MHz trans mit fre quency and -2 dB acous tic out put (equiv a lent to 0.22 MPa peakto-peak pres sure mea sured with a tank and hydrophone setup) from the SonixRP scan ner were se lected to elicit the subharmonic re sponse in the growth stage at 1.25 MHz for the Sonazoid microbubbles. [9][10][11] The acous tic out put set ting is ad just able on the SonixRP scan ner and is coded in dec re ments of 2 dB, with the max i mum acous tic out put rep re sented by 0 dB. Note that 0.22 MPa used here was less than the op ti mum in ci dent acous tic pres sure for SHAPE ap pli ca tions with Sonazoid microbubbles (0.39 MPa 10 ) as de ter mined with sin gle el e ment trans duc ers.…”

“…9,10 Pre vi ous stud ies in volv ing dy namic flow set-up with dif fer ent com mer cially-avail able ul tra sound scan ners prove that the SHAPE tech nique may be im ple mented on dif fer ent hard ware plat forms. 10,11 Cur rently var i ous tech niques are be ing de vel oped (and tested) for subharmonic im ag ing; [12][13][14][15] how ever, the ef fort in de vel op ing and test ing ap pro pri ate pro cess ing tech niques to uti lize the subharmonic emis sions for am bi ent pres sure es ti ma tion is lag ging. Since the SHAPE ap proach may re duce/elim i nate the number of catheterizations (and con se quently the as so ci ated costs and com pli ca tions) cur rently re quired for in vivo clin i cal am bi ent pres sure es ti ma tion, 16,17 de vel op ing a ro bust pro cess ing tech nique for SHAPE is re quired be fore the clin i cal ap pli ca tions can be in ves ti gated.…”

Effects of encapsulation damping on the excitation threshold for subharmonic generation from contrast microbubbles

“…They generate subharmonic signals that are utilized for subharmonic imaging-imaging at frequencies half that of the excitation (Forsberg et al, 2000;Shankar et al, 1998;Shankar et al, 1999). Variation of the subharmonic response with ambient pressure is also being investigated for developing a noninvasive organ-level blood pressure monitoring technique (Adam et al, 2005;Andersen and Jensen, 2010;Dave et al, 2011;Forsberg et al, 2005;Frinking et al, 2010;Leodore et al, 2007;Shi et al, 1999). Therefore, accurate prediction of the subharmonic response from contrast microbubbles is a topic of great interest (Eller and Flynn, 1968;Faez et al, 2011;Kimmel et al, 2007;Paul et al, 2010;Prosperetti, 1976Prosperetti, , 1977Sijl et al, 2010).…”