Ultrasound Exposimetry Using Liquid Crystal Plates

Liquid crystal-based sonosensitive plates will be investigated for rapid determination of spatial distributions of temporal average intensities for diagnostic ultrasound beams, including real-time imaging and Doppler modes. From such distributions, exposure parameters such as SPTA (spatial peak-temporal average) and SATA (spatial average-temporal average) can be determined. In this approach, ultrasonic field is visualized directly on the plate as the liquid crystal molecules are reoriented by the ultrasonic field from their initial unidirectional orientation. Then, an electric field is applied to restore the orientation of the molecules. The magnitude of the restoring electric field is then used to determine the sonographic exposure parameters. The approach offers several advantages over presently used hydrophone and radiation force balance methods. For example, image of the cross-sectional field distribution is available at once. Moreover, the distribution of temporal average intensity over the plane perpendicular to the propagation axis is available at once from the electric field data. In comparison, the hydrophone method is cumbersome as point-by-point detection of a large number of sample points is needed to determine field distribution. The radiation force balance method, on the other hand, requires an elaborate set-up and provides no information on the spatial distribution of the ultrasonic field.