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Dose Reduction Potential for Axial Step-And-Shoot CT Protocols Compared to Helical CT Acquisition
M Seal1,2 , E Somasundaram2 , N Artz2 , R Kaufman2 , S Brady2*, (1) University of Memphis, Memphis, TN, (2) St. Jude Children's Research Hospital, Memphis, TN
Presentations
SU-K-201-7 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 201
Purpose: Investigate dose reduction potential for axial step-and-shoot versus helical acquisition.
Methods: Due to its wide collimation potential (160 mm maximum), axial-only scan protocols were established for a GE Revolution. The metrics of noise texture (average NPS), total noise (1/mAs ∫NPS df), and resolution (50% MTF) were used to benchmark reconstructed image quality for axial and helical imaging. For axial examination dosimetry, the SSDE and mean CT number were calculated at each reconstructed slice and used to determine locations of neck-shoulder, lung, and abdomen/pelvic regions. Mean SSDE for each region was calculated and used to estimate organ dose. Helical organ dosimetry (GE VCT-XTe) was calculated using Monte Carlo and computational phantoms (VirtualDoseTMCT) incorporating patient CT examination parameters, actual scan coverage lengths, and over-ranging dose effects. Effective dose was calculated from estimated organ dose values.
Results: 169 axial examinations were prospectively analyzed for 94 Chest, 42 Chest-Abdomen-Pelvis (CAP), 27 Neck-Chest-Abdomen Pelvis (NCAP), and 6 Abdomen-Pelvis (Abd/Pel). 186 helical examinations were retrospectively analyzed for 101 Chest, 51 CAP, 27 NCAP, and 6 Abd/Pel. The mean patient weight was 49±30 kg (range 5-180 kg) and mean age was 12±6 yr (range 0.5-25 yr). Axial vs helical reconstructed image quality metrics were: total noise 0.58 vs 0.34 HU2 cm2 mAs-1, noise texture 0.35 vs 0.37 lp/cm, and resolution 0.44 vs 0.4 lp/cm. Dose reduction for Chest, Abd/Pel, CAP, and NCAP was calculated to be better than 32%, 21%, 29%, and 5% for axial scans. Population dose variation decreased by 61% for axial imaging with a median interquartile range (IQR) of 1.2 mSv (range 0.5-2.4 mSv) and 3.1 mSv (range 1-8 mSv) for axial and helical, respectively.
Conclusion: Image quality between axial and helical imaging protocols was Similar. Axial acquisition dose reduction potential was >21%, where the primary dose reduction came from eliminating over-ranging dose.
Funding Support, Disclosures, and Conflict of Interest: This work was partially funded by American Lebanese Syrian Associated Charities (ALSAC)
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