Seminar: Point Spread Function in Ultrasound Imaging

Student: Shivani Sharma

Supervisor: Dr. Yuan Xu

Abstract

Ultrasound Imaging plays an important part in medical diagnostic imaging. It has emerged as a
low cost, mobile, non invasive and real time imaging modality. The focus of the current study is
to derive explicit expressions for the Point Spread Function of various modes of ultrasound
imaging and apply the expressions to address various imaging quality issues.
PSF is the most important tool to describe an imaging system. It can be used to describe the
spatial resolution and contrast transfer of an imaging system. However, there are only a few
studies on the PSF of ultrasound imaging systems due to the nature of ultrasound image
reconstruction that is not easy for theoretical analysis. There are studies in literature that
address the modeling of conventional ultrasound imaging systems and coherent plane wave
compounding in special cases, but literature lacks the explicit expression for general ultrasound
imaging. The explicit expression can only be found for B-mode imaging at the focus point. One
goal of this project is to find the explicit expression for all the modes of ultrasound imaging at
any point of the imaging field.
In the first phase of the project, the primary goal of this research is to determine the Point
Spread Function in the context of Synthetic Transmit Aperture. The theoretical derivation is
extracted from one of the previous students' thesis of our group. This is the foundation to study
for modeling the theoretical PSF for STA and further comparing these results to that of the
simulation software tool (Field II). The preliminary analysis results are looking quite promising,
and we are summarizing the preliminary results in a manuscript and extending them to more
general cases.
In the second phase of the project, I'll extend the theoretical derivation for STA in the first phase
to the B-mode and the planar wave imaging. The extension to these modes would improve the
impact of the theoretical study on clinical applications and contribute to a more comprehensive
understanding of the Point Spread Function (PSF) in different ultrasound imaging scenarios.
In the third phase of the project, the above theoretical results will be used to address various
imaging quality issues. The potential topics include:
1) Estimation of the covariance matrix: The modeled PSF can be used to determine the
covariance matrix that will simplify the docorelation procedure.
2) Phase aberration: Investigating and mitigating the effects of phase aberration in ultrasound
imaging, this distorts the ultrasound wavefront and further impacts image quality.
3) Image resolution improvement through the deconvolution with respect to the point spread
function: Exploring techniques such as deconvolution to enhance image resolution by
compensating for the blurring effects introduced by the imaging system.
4) Ultrasound superresolution imaging. Point spread function is used in ultrasound
superresolution imaging, a method aiming to surpass the diffraction limit and improve spatial
resolution. A fast and accurate method to estimate point spread function is expected to improve
the performance of Ultrasound superresolution imaging.