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Comparison Study of Image Quality of Direct and Indirect Conversion Digital Mammography System
Korean Journal of Medical Physics 2010;21(3):239-245
Published online September 25, 2010
© 2010 Korean Society of Medical Physics.

Hye-Suk Park*, Yuna Oh, Hee-Jeong Jo, Sang Tae Kim§, Yu-Na Choi*, Hee-Joung Kim*

*Department of Radiological Science, College of Health Science and Research Institute of Health Science, Yonsei University, Wonju, Department of Radiology, Seoul National University Bundang Hospital, Seongnam, §Department of Radiation Science & Technology, Chonbuk National University, Jeonju, Korea
Abstract
The purpose of this study is to comprehensively compare and evaluate the characteristics of image quality for digital mammography systems which use a direct and indirect conversion detector. Three key metrics of image quality were evaluated for the direct and indirect conversion detector, the modulation transfer function (MTF), normalized noise power spectrum (NNPS), and detective quantum efficiency (DQE), which describe the resolution, noise, and signal to noise performance, respectively. DQE was calculated by using a edge phantom for MTF determination according to IEC 62220-1-2 regulation. The contrast to noise ratio (CNR) was evaluated according to guidelines offered by the Korean Institute for Accreditation of Medical Image (KIAMI). As a result, the higher MTF and DQE was measured with direct conversion detector compared to indirect conversion detector all over spatial frequency. When the average glandular dose (AGD) was the same, direct conversion detector showed higher CNR value. The direct conversion detector which has higher DQE value all over spatial frequency would provide the potential benefits for both improved image quality and lower patient dose in digital mammography system.
Keywords : Digital mammography system, Direct conversion detector, Indirect conversion detector, MTF, NNPS, DQE


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