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Quantification of head and body CTDI VOL of dual‐energy x‐ray CTwith fast‐kVp switching
Author(s) -
Li Baojun,
Yadava Girijesh,
Hsieh Jiang
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3582701
Subject(s) - imaging phantom , scanner , dosimetry , nuclear medicine , image quality , mockup , energy (signal processing) , materials science , biomedical engineering , medical physics , physics , computer science , medicine , optics , artificial intelligence , quantum mechanics , image (mathematics) , composite material
Purpose: Recently, a fast‐kVp switching (FKS) dual‐energy method has been presented with clinical and phantom results to demonstrate its efficacy. Patient dose concern has been raised on FKS dual‐energy since it involves higher energy acquisition at 140 kVp and slower gantry rotation time (e.g., 0.9–1 s) as opposed to 0.5 s as used in routine single‐energy exams. The purpose of our study was to quantitatively compare the CTDI VOL of FKS and routine CT exams under the body and head conditions.Methods: For a fair comparison, we have to overcome the difficulty of unmatched protocols between FKS and routine CT exams. In this paper, we propose to match the low contrast detectability (LCD), a critical image quality metric impacting diagnostic quality, before measuring CTDI VOL . The kVp pair, flux ratio, and optimal monochromatic energy have been carefully optimized for FKS protocols prior to the comparison. Our baseline single‐energy protocols were per IEC‐61223‐3‐5 under head and body conditions except for mA, which was iteratively adjusted to match the LCD of FKS. CTDI VOL was measured using either a 16 cm (for head scanning) or a 32 cm (for body scanning) PMMA phantom of at least 14 cm in length. The LCD was measured using the uniform section of Catphan 600. To make the study repeatable, the automated statistical LCD measurement tool available on GE Discovery CT750 scanner was used in this work. A visual LCD phantom and a Gammex tissue characterization phantom were also employed to verify the statistical LCD measurements and to introduce various patient sizes and contrast levels.Results: The mean CTDI VOL for the head and body single‐energy acquisitions was 57.5 and 29.2 mGy, respectively. The LCD was measured at 0.45% and 0.42%, respectively. The average CTDI VOL for FKS head and body scans was 70.4 and 33.4 mGy, respectively. The corresponding LCD was measured at 0.45% and 0.43%, respectively. The results from the visual LCD phantom and Gammex phantom supported the statistical LCD measurements.Conclusions: For equal image quality as measured by low contrast detectability, the CTDI VOL of a FKS head and body exam is roughly 22% and 14% higher than that of a routine single‐energy head and body exam, respectively, for the phantom measured.