title: Subharmonic contrast microbubble signals for noninvasive pressure estimation under static and dynamic flow conditions.
abstract: Our group has proposed the concept of subharmonic aided pressure estimation (SHAPE) utilizing microbubble-based ultrasound contrast agent signals for the noninvasive estimation of hydrostatic blood pressures. An experimental system for in vitro SHAPE was constructed based on two single-element transducers assembled confocally at a 60 degree angle to each other. Changes in the first, second and subharmonic amplitudes of five different ultrasound contrast agents were measured in vitro at static hydrostatic pressures from 0-186 mmHg, acoustic pressures from 0.35-0.60 MPa peak-to-peak and frequencies of 2.5-6.6 MHz. The most sensitive agent and optimal parameters for SHAPE were determined using linear regression analysis and implemented on a Logiq 9 scanner (GE Healthcare, Milwaukee, WI). This implementation of SHAPE was then tested under dynamic-flow conditions and compared to pressure-catheter measurements. Over the pressure range studied, the first and second harmonic amplitudes reduced approximately 2 dB for all contrast agents. Over the same pressure range, the subharmonic amplitudes decreased by 9-14 dB and excellent linear regressions were achieved with the hydrostatic pressure variations (r = 0.98, p < 0.001). Optimal sensitivity was achieved at a transmit frequency of 2.5 MHz and acoustic pressure of 0.35 MPa using Sonazoid (GE Healthcare, Oslo, Norway). A Logiq 9 scanner was modified to implement SHAPE on a convex transducer with a frequency range from 1.5-4.5 MHz and acoustic pressures from 0-3.34 MPa. Results matched the pressure catheter (r2 = 0.87). In conclusion, subharmonic contrast signals are a good indicator of hydrostatic pressure. Out of the five ultrasound contrast agents tested, Sonazoid was the most sensitive for subharmonic pressure estimation. Real-time SHAPE has been implemented on a commercial scanner and offers the possibility of allowing pressures in the heart and elsewhere to be obtained noninvasively.
authors.affiliation: Department of Radiology, Thomas Jefferson University, Philadelphia, PA 19107, USA.
authors.forename: Valgerdur G
authors.initials: VG
authors.lastname: Halldorsdottir
authors.forename: Jaydev K
authors.initials: JK
authors.lastname: Dave
authors.forename: Lauren M
authors.initials: LM
authors.lastname: Leodore
authors.forename: John R
authors.initials: JR
authors.lastname: Eisenbrey
authors.forename: Suhyun
authors.initials: S
authors.lastname: Park
authors.forename: Anne L
authors.initials: AL
authors.lastname: Hall
authors.forename: Kai
authors.initials: K
authors.lastname: Thomenius
authors.forename: Flemming
authors.initials: F
authors.lastname: Forsberg
mesh_terms: D000162:Acoustics; D001795:Blood Pressure Determination / Q000379:methods*; D003287:Contrast Media / Q000493:pharmacokinetics*; D004867:Equipment Design; D006331:Heart Diseases / Q000000981:diagnostic imaging; D006801:Humans; D006874:Hydrostatic Pressure; D066298:In Vitro Techniques; D016018:Least-Squares Analysis; D016014:Linear Models; D045423:Microbubbles; D019047:Phantoms, Imaging; D014159:Transducers; D014463:Ultrasonography / Q000379:methods*; D014652:Vascular Diseases / Q000000981:diagnostic imaging
chemical_list: D003287:Contrast Media