Computer simulation studies of ultrasound Doppler color flow images

Ultrasound Doppler color flow imaging uses pulse-echo imaging techniques and pulsed Doppler methods to produce two-dimensional information of the structure and function of tissues within the human body in real-time. Flow imaging systems are very complex and there are many factors related to the tissue being imaged and related to the system itself that influence the flow image that is observed. The general goal of gaining a better understanding of the properties of flow images and the limitations of flow imaging systems is sought in this thesis for the purpose of advancing the clinical utility of flow imaging.; In this thesis, I describe the extension of pulse-echo image simulation techniques based on point scattering theory to the field of flow imaging. This has required the development of a robust and computationally intense numerical approach. Initially, methods used for B-scan simulation were applied but these ultimately required significant modification for simulation of flow images free of numerical artifacts. The simulation tool was applied to studying first the properties of the flow image process when large vessels are imaged. The simulated images demonstrate that the observed flow dynamics are highly dependant on and sensitive to changes in system parameters. In particular, parameters which can be easily changed in a clinical system played a significant role in determining the appearance of the flow image.; The simulation was next applied to study the use of flow imaging in small vessel {dollar}(<{dollar}2 mm) flow measurement. Many of the fundamental limitations of flow imaging become apparent in the imaging of small vessels. This is basically due to the low velocities and low signal amplitudes that must be detected, compared to higher velocities and stronger signals from large vessels. The results of this study attempt to demonstrate what specific factors are most limiting in the use of flow imaging. As the vessel size approaches the system spatial resolution, it was found that quantitative capabilities achievable in large vessels are clearly lost. However, vessels of importance to tumor imaging that are much smaller than the resolution can be detected.