Effect of spatial-domain pulse width on the resolution of scattering images in ultrasound computed tomography

Abstract

Full-aperture tomography (FAT) is the major image reconstruction method for a circular ring array (CRA)-based ultrasound computed tomography (USCT) system. The FAT technique requires transferring the reconstruction process from the temporal domain to the spatial domain, during which the imaging resolution of the USCT is degraded by the spatial-domain pulse width (SDPW) of backprojection areas. To tackle this challenge, this study investigates the characteristics of the SDPW and how it degrades the image resolution. We show that the SDPW depends on the frequency of the ultrasound and the position of the transmitting elements, receiving elements and the imaging point. To quantify the deterioration of image resolution associated with the position of the transmitting and receiving elements, a SDPW broadening factor (SDPWBF) is introduced. The results of numerical simulation show a smaller SDPWBF provides a better reflection image resolution, and the distribution of SDPWBF shows that a shorter distance between the receiving element and the transmitting element yields a smaller SDPWBF. The SDPWBF is therefore able to be an indicator of selecting the signals acquired from the transmitting and receiving elements to perform optimal image resolution. Single-scatterer phantom and in vivo experiments demonstrate how the SDPWBF affects the USCT image spatial resolution and signal-to-noise ratio (SNR), and the results agree well with the theoretical predictions.