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TU‐EE‐A3‐01: CT Number Accuracy of Simulated Lung Nodules Imaged with a Multi‐Detector CT Scanner
Author(s) -
Goodsitt M,
Chan H,
Larson S,
Christodoulou E,
Kim J,
Way T
Publication year - 2005
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 - 10.1118/1.1998430
Subject(s) - imaging phantom , nodule (geology) , nuclear medicine , water equivalent , scanner , materials science , tomography , medicine , radiology , physics , optics , meteorology , snow , biology , paleontology
Purpose: To investigate the accuracies of the CT♯'s of simulated lung nodules for a QCT technique. Method and Materials: Spherical balls of 4 diameters (3.2,4.8,9.5 and 16‐mm) and 2 compositions (50mg/cc and 100mg/cc CaCO 3 ) were employed as simulated lung nodules. All were scanned in a liquid water‐filled container at the center of a 20‐cm diameter water‐equivalent‐plastic phantom using GE multi‐detector CT scanners. A subset of the nodules and some 6.2‐mm diameter acrylic balls were also scanned in a simulated lung region within a thorax section phantom that was bolused on both sides with water‐equivalent slabs. Based on initial results that showed a significant decrease in the CT♯ of a nodule when scanned in the thorax section, additional studies were performed with 2 size air cavities at the center of the water phantom. Results: The CT♯'s of the nodules in water were fairly independent of nodule size (average CT♯'s of 50mg/cc=59–66HU and 100mg/cc=108–115HU). The CT♯ of a 50mg/cc nodule scanned at the center of the water phantom was 66HU in water, 51HU in a 2‐cm air cavity and 36HU in a 4.9‐cm air cavity. The CT♯'s of the acrylic balls ranged from about 79 to 96HU within the lung section and had poor‐to‐good reproducibility on repeat scans (CT♯ changes of +19HU, −17HU and 1HU for 3 different balls). Conclusion: The CT♯ of a nodule is highly dependent upon the amount of air or low‐density lung tissue near the nodule. We believe this error is due to the assumed all‐water composition of the patient/phantom in the scanner's beam hardening correction algorithm. The unusual reproducibility of the CT♯'s of nodules in the thorax phantom is likely a combined effect of sub‐millimeter air gaps between the phantom sections and variability in helical scanning interpolation. Further studies and possible solutions will be discussed.