title: Variability of CT Attenuation Measurements in Virtual Unenhanced Images Generated Using Multimaterial Decomposition from Fast Kilovoltage-switching Dual-energy CT.
abstract: To compare Hounsfield unit (HU) data obtained from true-unenhanced (TUE) and virtual-unenhanced (VUE) imaging obtained with a fast kv-switching dual-energy computed tomography (CT) scanner using multimaterial decomposition algorithm.
  
  
  
  In this Institutional Review Board-approved, Health Insurance Portability and Accountability Act-compliant, retrospective cohort study, CT scans of 19 patients undergoing multiphasic renal protocol abdominal CT on a fast kv-switching dual-energy CT scanner were reviewed. CT numbers were measured on the matched TUE and VUE generated using a multimaterial decomposition algorithm with selective iodine suppression, and postcontrast images at predefined locations in seven organs. Six hundred sixty regions of interest were placed at 132 locations. Agreement was assessed with paired t test, Pearson's correlation, and Bland-Altman analysis.
  
  
  
  Mean TUE and VUE measurements were not significantly different in the corticomedullary (P = 0.25) or nephrographic (P = 0.10) phases. There was a strong correlation between TUE and VUE CT numbers (corticomedullary: r = 0.90, nephrographic: r = 0.90, each P < 0.001). Discrepancies ≥5 HU occurred 46 times (35%, 46 of 132) in the corticomedullary phase and 44 times (33%, 44 of 132) in the nephrographic phase. Discrepancies ≥10 HU occurred in 7% (9 of 132 in both corticomedullary and nephrographic phases). Interphase, intrasubject VUE CT numbers were strongly correlated (r = 0.93, P < 0.001), but discrepancies ≥5 HU (22% [29 of 132]) and ≥10 HU (2% [3 of 132]) occurred. There was no significant correlation between the true postcontrast CT number and the magnitude of VUE-TUE discrepancy (r = -0.04, P = 0.6).
  
  
  
  CT numbers on VUE images generated from fast kv-switching dual-energy CT scans strongly correlate with TUE CT numbers on a population basis, but commonly vary 5-9 HU on a per-patient basis.
authors: Department of Radiology, Division of Abdominal Imaging, University of Michigan Health System, University of Michigan Hospital, Ann Arbor, Michigan 48109. Electronic address: ravikaza@med.umich.edu.
authors: Ravi K
authors: RK
authors: Kaza
authors: Department of Radiology, Division of Abdominal Imaging, University of Michigan Health System, University of Michigan Hospital, Ann Arbor, Michigan 48109; Department of Radiology, University of Southern California, Los Angeles, California.
authors: Evan A
authors: EA
authors: Raff
authors: Department of Radiology, Division of Abdominal Imaging, University of Michigan Health System, University of Michigan Hospital, Ann Arbor, Michigan 48109.
authors: Matthew S
authors: MS
authors: Davenport
authors: Michigan Institute for Clinical and Health Research, University of Michigan, Ann Arbor, Michigan.
authors: Shokoufeh
authors: S
authors: Khalatbari
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D003287:Contrast Media; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D007479:Iopamidol; D007668:Kidney / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D011856:Radiographic Image Enhancement; D011860:Radiography, Abdominal / Q000295:instrumentation / Q000379:methods; D015900:Radiography, Dual-Energy Scanned Projection / Q000379:methods; D015203:Reproducibility of Results; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000295:instrumentation / Q000379:methods*
chemical_list: D003287:Contrast Media; D007479:Iopamidol
keywords: Dual-energy CT; Virtual unenhanced imaging; multimaterial decomposition