BackgroundThe accuracy of vector flow mapping (VFM) was investigated in comparison to stereo particle image velocimetry (stereo-PIV) measurements using a left ventricular phantom. VFM is an echocardiographic approach to visualizing two-dimensional flow dynamics by estimating the azimuthal component of flow from the mass-conservation equation. VFM provides means of visualizing cardiac flow, but there has not been a study that compared the flow estimated by VFM to the flow data acquired by other methods.MethodsA reproducible three-dimensional cardiac blood flow was created in an optically and acoustically transparent left-ventricle phantom, that allowed color-flow mapping (CFM) data and stereo-PIV to be simultaneously acquired on the same plane. A VFM algorithm was applied to the CFM data, and the resulting VFM estimation and stereo-PIV data were compared to evaluate the accuracy of VFM.ResultsThe velocity fields acquired by VFM and stereo-PIV were in excellent agreement in terms of the principle flow features and time-course transitions of the main vortex characteristics, i.e., the overall correlation of VFM and PIV vectors was R = 0.87 (p < 0.0001). The accuracy of VFM was suggested to be influenced by both CFM signal resolution and the three-dimensional flow, which violated the algorithm’s assumption of planar flow. Statistical analysis of the vectors revealed a standard deviation of discrepancy averaging at 4.5% over the CFM velocity range for one cardiac cycle, and that value fluctuated up to 10% depending on the phase of the cardiac cycle.ConclusionsVFM provided fairly accurate two-dimensional-flow information on cardio-hemodynamics. These findings on VFM accuracy provide the basis for VFM-based diagnosis.

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To apply superheated perfluorocarbon nanodroplets to tumor diagnosis and treatment, acoustic signals formed upon the vaporization of droplets in tissue-mimicking phantoms were measured with 3 MHz ultrasound. A characteristic impulse wave was associated with phase change induction with 100 cycles of ultrasound at a 9 MPa peak negative pressure, observed as an intensity change in B-mode imaging. In addition, the subsequent impulse waves were observed only from the phase change induction in gels. Therefore, these subsequent impulse waves were suggested to be characteristic features of the vaporization of superheated nanodroplets at rigid boundaries. Furthermore, such impulse waves reflect the properties of surrounding environments such as elasticity and viscosity in the gel. The findings of this study would lead to a novel microscale tissue characterization method applicable to local sites. #

An in vitro feasibility test for a novel ultrasound therapy using a type of superheated perfluorocarbon droplet, phase-change nanodroplet (PCND), was performed in gel phantoms with the goal of high selectivity and low invasiveness. Measurements of broadband signal emission revealed that a triggering ultrasound pulse (peak negative pressure of 2.4 MPa) reduces the pressure threshold for cavitation induced by a subsequent ultrasound exposure at an order of magnitude from 2.4 to 0.2 MPa. The maximum allowed interval between the two ultrasound exposures for inducing cavitation with 100- and 1,000-cycle triggering ultrasound was about 100 and 500 ms, respectively. The echo signal increases induced by the triggering ultrasound with 100- and 1000-cycles were enhanced and suppressed by the subsequent ultrasound exposure, respectively. This different behavior seemed to be due to the presence of enlarged free bubbles, which should be avoided for the localization of therapeutic effects.

The combination of pHIFU and PCND exerted a significant anti-tumor effect and may be a new candidate for treatment of locally advanced cancer.