OBJECTIVE: To compare computed tomography dose and noise arising from use of an automatic exposure control (AEC) system designed to maintain constant image noise as patient size varies with clinically accepted technique charts and AEC systems designed to vary image noise. MATERIALS AND METHODS: A model was developed to describe tube current modulation as a function of patient thickness. Relative dose and noise values were calculated as patient width varied for AEC settings designed to yield constant or variable noise levels and were compared to empirically derived values used by our clinical practice. Phantom experiments were performed in which tube current was measured as a function of thickness using a constant-noise-based AEC system and the results were compared with clinical technique charts. RESULTS: For 12-, 20-, 28-, 44-, and 50-cm patient widths, the requirement of constant noise across patient size yielded relative doses of 5%, 14%, 38%, 260%, and 549% and relative noises of 435%, 267%, 163%, 61%, and 42%, respectively, as compared with our clinically used technique chart settings at each respective width. Experimental measurements showed that a constant noise-based AEC system yielded 175% relative noise for a 30-cm phantom and 206% relative dose for a 40-cm phantom compared with our clinical technique chart. CONCLUSIONS: Automatic exposure control systems that prescribe constant noise as patient size varies can yield excessive noise in small patients and excessive dose in obese patients compared with clinically accepted technique charts. Use of noise-level technique charts and tube current limits can mitigate these effects.
OBJECTIVE: To compare computed tomography dose and noise arising from use of an automatic exposure control (AEC) system designed to maintain constant image noise as patient size varies with clinically accepted technique charts and AEC systems designed to vary image noise. MATERIALS AND METHODS: A model was developed to describe tube current modulation as a function of patient thickness. Relative dose and noise values were calculated as patient width varied for AEC settings designed to yield constant or variable noise levels and were compared to empirically derived values used by our clinical practice. Phantom experiments were performed in which tube current was measured as a function of thickness using a constant-noise-based AEC system and the results were compared with clinical technique charts. RESULTS: For 12-, 20-, 28-, 44-, and 50-cm patient widths, the requirement of constant noise across patient size yielded relative doses of 5%, 14%, 38%, 260%, and 549% and relative noises of 435%, 267%, 163%, 61%, and 42%, respectively, as compared with our clinically used technique chart settings at each respective width. Experimental measurements showed that a constant noise-based AEC system yielded 175% relative noise for a 30-cm phantom and 206% relative dose for a 40-cm phantom compared with our clinical technique chart. CONCLUSIONS: Automatic exposure control systems that prescribe constant noise as patient size varies can yield excessive noise in small patients and excessive dose in obesepatients compared with clinically accepted technique charts. Use of noise-level technique charts and tube current limits can mitigate these effects.
Authors: Chang Hyun Lee; Jin Mo Goo; Hyun Ju Ye; Sung-Joon Ye; Chang Min Park; Eun Ju Chun; Jung-Gi Im Journal: Radiographics Date: 2008 Sep-Oct Impact factor: 5.333
Authors: Kyle McMillan; Maryam Bostani; Christopher H Cagnon; Lifeng Yu; Shuai Leng; Cynthia H McCollough; Michael F McNitt-Gray Journal: Med Phys Date: 2017-06-30 Impact factor: 4.071
Authors: Christopher P Favazza; Xinhui Duan; Yi Zhang; Lifeng Yu; Shuai Leng; James M Kofler; Michael R Bruesewitz; Cynthia H McCollough Journal: Phys Med Biol Date: 2015-10-13 Impact factor: 3.609