Integration of a CMUT linear array for wideband H-scan ultrasound imaging

A new modality has recently emerged for the ultrasound (US) classification of acoustic scatterers. Termed H-scan US, this imaging approach links the mathematics of Gaussian-weighted Hermite functions to the physics of scattering and reflection from different tissue structures within a standard convolutional model of pulse-echo US systems. The purpose of this study was to evaluate the use of a capacitive micromachined ultrasonic transducer (CMUT) for improved H-scan US imaging. Image data was acquired using a programmable US scanner (Vantage 256, Verasonics Inc) equipped with a 256-element L22-8v CMUT linear array transducer (Kolo Medical). Plane wave imaging was performed at a center frequency of 15 MHz. To generate the H-scan US image, three parallel convolution filters were applied to the radio frequency (RF) data to measure the relative strength of the received signals. After envelope detection, the relative strength of the filter outputs is color-coded to represent relative scatterer size. In vitro studies involved use of gelatin-based homogeneous phantoms that had different-sized spherical US scatterers, namely, 15, 30, or 45 μm. In vivo imaging of a breast tumor-bearing mouse was also used to test the new wideband H-scan US system. Results indicated that scatterers above 15 μm began to show good separation in the different Hermite. Findings from H-scan US imaging of a breast tumor- bearing mouse demonstrated that tumor tissue has a heterogenous distribution of scattering structures. Overall, H-scan US imaging is a promising approach for tissue classification and estimation of relative scatterer size.