Identifier

etd-0920102-144012

Abstract

"This study characterizes the image quality parameters of a clinical full-field digital mammography system at various x-ray spectral conditions. The energy of the incident x-ray beam, the spectral characteristics, and breast thickness impact the physical performance such as the detective quantum efficiency of the system, thereby affecting the overall performance. The modulation transfer function, noise power spectrum were measured without the anti-scatter grid, and the detective quantum efficiency was calculated for different incident x-ray conditions. Detective quantum efficiency was also calculated with the anti-scatter grid placed above the detector to study its impact. Results indicate a substantial drop in the detective quantum efficiency with the anti-scatter grid under certain conditions. It was also determined that detective quantum efficiency decreases as x-ray beam hardening is increased. A spatial frequency-dependent cascaded liner systems model was developed to predict the detective quantum efficiency of the system for different target-filter combinations. This theoretical model is based upon a serial cascade approach in which the system is conceptually divided into a number of discrete stages. Each stage represents a physical process having intrinsic signal and noise transfer properties. A match between the predicted data and the experimental detective quantum efficiency data confirmed the validity of the model. Contrast-detail performance, a widely used quality control tool to assess clinical imaging systems, for the clinical full-field digital mammography was studied using a commercially available CDMAM phantom to learn the effects of Joint Photographic Experts Group 2000 (JPEG2000) compression technique on detectability. A 4-alternative forced choice experiment was conducted. The images were compressed at three different compression ratios (10:1, 20:1 and 30:1). From the contrast-detail curves generated from the observer data at 50% and 75% threshold levels, it was concluded that uncompressed images exhibit lower (better) contrast-detail characteristics than compressed images but a certain limit to compression, without substantial loss of visual quality, can be used."

Publisher

Worcester Polytechnic Institute

Degree Name

MS

Department

Biomedical Engineering

Project Type

Thesis

Date Accepted

2002-09-20

Accessibility

Unrestricted

Subjects

mammography, linear cascade model, screen-film, Breast, Radiography, Radiography, Medical, Digital techniques

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