DEVELOPMENT AND CHARACTERIZATION OF A HIGH ENERGY PHASE CONTRAST X-RAY IMAGING SYSTEM PROTOTYPE

Abstract

The field of mammography receives constant research attention focused on improving the balance between the benefits of cancer screening and the risks of harmful radiation to the patient. As a result, numerous advancements have been made throughout the history of mammography, which have not only improved the ability to detect cancer at an earlier stage, but also to diagnose previously undetectable cancer. Numerous clinical trials have demonstrated the decrease in mortality rates. Due to the potential for saving lives, along with the recent public concerns regarding radiation dose, significant research attention remains focused on investigating methods for further improving the detection capabilities and reducing the radiation dose. However, the similar absorption characteristics of normal and malignant tissue present a challenge in differentiating between them using conventional x-ray imaging. The current method for providing higher image quality involves utilizing anti-scatter grids and operating at much lower x-ray energies than other radiography fields, both of which result in an increased radiation dose. An emerging technology called phase contrast imaging, which is based not only on absorption but also the effects produced by x-ray phase changes, holds the potential to increase the x-ray energy and remove the grid without compromising the image quality, which could reduce the patient dose and thus benefit the field of mammography. Preliminary studies in phase contrast imaging at the same energy as conventional imaging have indicated the ability to reduce the radiation dose without negatively impacting the diagnosis capabilities. However, existing challenges in clinical implementation have prevented the technology from further progress.

The goal of the research presented in this dissertation comprises a thorough investigation of the potential of high energy phase contrast imaging to overcome these challenges and further reduce the radiation dose without decreasing the detection ability. Following an introductory chapter, Chapter 2 presents a detailed description of the necessary methods required to perform the dissertation research. The methods are separated into four categories: image quality, statistical methods, phase contrast imaging, and radiation dose. Chapters 3 through 6 encompass four preliminary studies accomplished to demonstrate a thorough understanding of the research methods, as well as to evaluate the feasibility of the research and corresponding motivation in the medical imaging field. The development and preliminary feasibility investigation of a high energy phase contrast imaging system prototype is presented in Chapter 7, followed by an image quality comparison to high and low energy conventional imaging with similar entrance exposures in Chapter 8. Chapter 9 presents a comprehensive image quality and dose comparison of high energy phase contrast and low energy conventional imaging. Finally, the summary and discussion of results are presented in Chapter 10, along with planned research direction for future studies.

This dissertation encompasses numerous original contributions, perhaps the most significant of which were the demonstration of the ability of phase contrast imaging to deliver acceptable image quality for detection and diagnosis at higher x-ray energies than investigated previously, as well as the comprehensive comparison of high energy phase contrast imaging with low energy conventional imaging. These results clearly demonstrate the ability of phase contrast imaging to sustain the image quality improvement at high x-ray energies and for clinical thicknesses without an increase in the radiation dose. In addition, each of the preliminary studies involved the development of novel methods or techniques to improve existing procedures. First, the step-by-step optimization of the MTF algorithm presented in Chapter 4 was an original approach, which also included the application of new methods to several of the steps, resulting in an optimized algorithm with significantly improved accuracy. Next, Chapter 5 presented the development of a quantitative method to determine the error contributed to any calculated result by each of the represented components, as well as a new method for calculating the magnification factor that considerably reduces the error, especially for clinical systems. Chapter 6 presented the novel application of the existing method of beam hardening to reduce the radiation dose without affecting the detection capability, which holds the potential to greatly benefit mammography and related fields.

The research presented in this dissertation is a strong indication of the potential of high energy phase contrast imaging to dramatically benefit x-ray imaging fields such as mammography by improving the ability to detect and diagnose diseases at earlier stages or when previously undetectable without increasing the radiation dose. The ability to improve the capability to diagnose disease without increasing the risk of harmful radiation to the patient would significantly improve the balance between the risks and benefits of cancer screening, which holds the potential to revolutionize the fields of x-ray imaging and lower mortality rates.