Premium
SU‐E‐J‐171: Variation of the Hounsfield Unit On CT Scanning Parameters and Reconstruction and Its Effect On Dose Calculations
Author(s) -
Lee J,
Chan R
Publication year - 2013
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 - 10.1118/1.4814383
Subject(s) - hounsfield scale , imaging phantom , nuclear medicine , scanner , iterative reconstruction , standard deviation , tomography , mathematics , computed tomography , physics , materials science , medicine , optics , radiology , statistics
Purpose: To assess the variation of Hounsfield units (HU) when using different CT scanning parameters. The effect of HU‐to‐electron density (ED) table on the accuracy of dose calculations was evaluated. Methods: A CIRS (model 62) phantom was used for all the tests. Various kVp, field‐of‐view(FOV), reconstruction algorithms with contribution of adaptive statistical iterative reconstruction(ASiR™) (0‐80%) were applied during the scanning process(GE lightspeed CT simulator). HU for each insert was measured. A HU‐ED table was acquired for Philips PET/CT scanner as well. A phantom and clinical cases were selected for dosimetric comparisons using different HU‐ED tables. Results: No significant difference in HU for low electron density material was observed regardless the scanning parameters. The dependency of HU on tube voltage and FOV was observed for bone‐equivalent materials. HU for dense bone scanned with 80kVp was 39.4% higher than HU with 120kVp. HU with small FOV relative to large FOV was 11.9% higher for trabecular bone. The maximum deviation was observed for bone‐equivalent material when the bone algorithm, producing a 6.2% change in HU, or 80% of ASiR™ contribution, were applied; however, the difference in HU was still within the standard deviation. The difference in HU between two scanners was less than the SD observed on GE CT simulator, except for liver‐and bone‐equivalent materials. Using a HU‐ED table with the worse case scenario (80kVp, bone reconstruction with 80% ASiR™), it was shown that the deviation was within 1% for phantom studies and −7.4%−2.7% for clinical cases. The maximum of 5.9% deviation was observed when calculated with a table from the different scanner. Conclusion: The maximum deviation in HU was observed for bone‐equivalent materials when low kVp was applied. Use of a wrong HU‐ED table could introduce −7.4%−2.7% dosimetric error at certain regions of interest.