OBJECTIVE: To assess effects of off-centering, automatic exposure control, and padding on attenuation values, noise, and radiation dose when using in-plane bismuth-based shields for CT scanning. MATERIALS AND METHODS: A 30 cm anthropomorphic chest phantom was scanned on a 64-multidetector CT, with the center of the phantom aligned to the gantry isocenter. Scanning was repeated after placing a bismuth breast shield on the anterior surface with no gap and with 1, 2, and 6 cm of padding between the shield and the phantom surface. The "shielded" phantom was also scanned with combined modulation and off-centering of the phantom at 2 cm, 4 cm and 6 cm below the gantry isocenter. CT numbers, noise, and surface radiation dose were measured. The data were analyzed using an analysis of variance. RESULTS: The in-plane shield was not associated with any significant increment for the surface dose or CT dose index volume, which was achieved by comparing the radiation dose measured by combined modulation technique to the fixed mAs (p > 0.05). Irrespective of the gap or the surface CT numbers, surface noise increased to a larger extent compared to Hounsfield unit (HU) (0-6 cm, 26-55%) and noise (0-6 cm, 30-40%) in the center. With off-centering, in-plane shielding devices are associated with less dose savings, although dose reduction was still higher than in the absence of shielding (0 cm off-center, 90% dose reduction; 2 cm, 61%) (p < 0.0001). Streak artifacts were noted at 0 cm and 1 cm gaps but not at 2 cm and 6 cm gaps of shielding to the surface distances. CONCLUSION: In-plane shields are associated with greater image noise, artifactually increased attenuation values, and streak artifacts. However, shields reduce radiation dose regardless of the extent of off-centering. Automatic exposure control did not increase radiation dose when using a shield.
OBJECTIVE: To assess effects of off-centering, automatic exposure control, and padding on attenuation values, noise, and radiation dose when using in-plane bismuth-based shields for CT scanning. MATERIALS AND METHODS: A 30 cm anthropomorphic chest phantom was scanned on a 64-multidetector CT, with the center of the phantom aligned to the gantry isocenter. Scanning was repeated after placing a bismuth breast shield on the anterior surface with no gap and with 1, 2, and 6 cm of padding between the shield and the phantom surface. The "shielded" phantom was also scanned with combined modulation and off-centering of the phantom at 2 cm, 4 cm and 6 cm below the gantry isocenter. CT numbers, noise, and surface radiation dose were measured. The data were analyzed using an analysis of variance. RESULTS: The in-plane shield was not associated with any significant increment for the surface dose or CT dose index volume, which was achieved by comparing the radiation dose measured by combined modulation technique to the fixed mAs (p > 0.05). Irrespective of the gap or the surface CT numbers, surface noise increased to a larger extent compared to Hounsfield unit (HU) (0-6 cm, 26-55%) and noise (0-6 cm, 30-40%) in the center. With off-centering, in-plane shielding devices are associated with less dose savings, although dose reduction was still higher than in the absence of shielding (0 cm off-center, 90% dose reduction; 2 cm, 61%) (p < 0.0001). Streak artifacts were noted at 0 cm and 1 cm gaps but not at 2 cm and 6 cm gaps of shielding to the surface distances. CONCLUSION: In-plane shields are associated with greater image noise, artifactually increased attenuation values, and streak artifacts. However, shields reduce radiation dose regardless of the extent of off-centering. Automatic exposure control did not increase radiation dose when using a shield.
Authors: Andrew N Primak; Cynthia H McCollough; Michael R Bruesewitz; Jie Zhang; Joel G Fletcher Journal: Radiographics Date: 2006 Nov-Dec Impact factor: 5.333
Authors: Jianhai Li; Unni K Udayasankar; Thomas L Toth; John Seamans; William C Small; Mannudeep K Kalra Journal: AJR Am J Roentgenol Date: 2007-02 Impact factor: 3.959
Authors: Mannudeep K Kalra; Michael M Maher; Thomas L Toth; Leena M Hamberg; Michael A Blake; Jo-Anne Shepard; Sanjay Saini Journal: Radiology Date: 2004-01-22 Impact factor: 11.105
Authors: Bradley L Fricke; Lane F Donnelly; Donald P Frush; Terry Yoshizumi; Vladimir Varchena; Stacy A Poe; Javier Lucaya Journal: AJR Am J Roentgenol Date: 2003-02 Impact factor: 3.959
Authors: Andrew J Einstein; Carl D Elliston; Daniel W Groves; Bin Cheng; Steven D Wolff; Gregory D N Pearson; M Robert Peters; Lynne L Johnson; Sabahat Bokhari; Gary W Johnson; Ketan Bhatia; Theodore Pozniakoff; David J Brenner Journal: J Nucl Cardiol Date: 2011-11-09 Impact factor: 5.952
Authors: Ranish Deedar Ali Khawaja; Sarabjeet Singh; Atul Padole; Alexi Otrakji; Diego Lira; Da Zhang; Bob Liu; Andrew Primak; George Xu; Mannudeep K Kalra Journal: Radiat Prot Dosimetry Date: 2017-08-01 Impact factor: 0.972
Authors: Dominik Ketelsen; Marius Horger; Markus Buchgeister; Michael Fenchel; Christoph Thomas; Nadine Boehringer; Maximilian Schulze; Ilias Tsiflikas; Claus D Claussen; Martin Heuschmid Journal: Korean J Radiol Date: 2010-08-27 Impact factor: 3.500