The purpose of this work was to measure radiation absorbed dose and its distribution in an anthropomorphic head phantom under clinically representative scan conditions in three widely-used computed tomography (CT) scanners, and to relate those dose values to metrics such as high-contrast resolution, noise, and contrast-to-noise ratio (CNR) in the American College of Radiology CT accreditation phantom. The OSLD measurements showed that the Siemens Definition and the Philips Brilliance scanners (located at two different clinical facilities) yield about the same average value of 43 mGy of absorbed dose in tissue. The GE Discovery delivers about the same amount of dose when run under similar operating and image-reconstruction conditions, i.e., without tube current modulation and ASIR. The image-metrics analysis likewise showed that the MTF, NPS, and CNR associated with the reconstructed images are mutually comparable when the three scanners are run with similar settings, and differences can be attributed to different edge-enhancement properties of the applied reconstruction filters. Moreover, when the GE scanner was operated with the facilitys actual scanner settings for routine head exams, which apply 50% ASIR and use only approximately half of the 100%-FBP dose, the CNR of the images showed no significant change.
Citation: Medical Physics
Pub Type: Journals
computed tomography, dose, OSL, phantom, image quality, CT