In-Silico Simulations of Ultrasound Imaging In the Far-Field for Therapy Monitoring
Abstract
Purpose
Ultrasound imaging is often used for therapy guidance, including focused ultrasound procedures. There is often a discrepancy between the designs of focused ultrasound source and diagnostic imaging probes, and target visualization can be in the far field of the imaging system. This discrepancy results in a reduced image quality, complicating interpretation of real-time monitoring. The purpose of this study was to develop and validate in-silico methods for three-dimensional ultrasound imaging capable of supporting real-time monitoring of cavitation clouds during histotripsy therapy.
Methods
A fully populated 32x32 matrix array was modeled to characterize three-dimensional point spread functions (PSFs) over focal depths ranging from 1.0 to 10.0 cm. The range exceeds that anticipated for most histotripsy systems. Axial and lateral PSF profiles were evaluated, and spatial resolution was quantified using the −6 dB full width at half maximum (FWHM). Linear regression was used to assess depth dependence and symmetry in lateral resolution.
Results
The axial PSF exhibited a narrow main lobe with sidelobes decaying below −50 dB within a few millimeters of the focus and remained approximately constant across all depths, with near-zero regression slope. In contrast, lateral PSF widths increased linearly with depth, showing strong symmetry between the x- and y-directions with identical regression fits. These results indicate depth-invariant axial resolution governed by pulse bandwidth and aperture-limited lateral resolution dominated by diffraction.
Conclusion
The proposed in-silico framework demonstrates predictable and stable three-dimensional imaging performance across clinically relevant depths, supporting reliable detection and characterization of cavitation activity. These findings address key limitations of two-dimensional monitoring and provide a foundation for real-time volumetric image guidance of histotripsy therapy.