title: CT Hounsfield numbers of soft tissues on unenhanced abdominal CT scans: variability between two different manufacturers' MDCT scanners.
abstract: OBJECTIVE
  The purpose of this study is to determine whether Hounsfield numbers of soft tissues on unenhanced abdominal CT of the same patient vary on repeat scans done on two different manufacturers' MDCT scanners.
  
  
  METHODS
  A database search was performed to identify patients older than 18 years who underwent unenhanced CT of the abdomen and pelvis performed both on a Volume CT (GE Healthcare) and a Definition AS Plus (Siemens Healthcare) 64-MDCT scanner within 12 months of each other. After excluding those patients for whom Hounsfield unit measurements would be affected by mitigating factors, 48 patients (mean age, 58.8 years) were identified. Hounsfield unit measurements were obtained in nine different soft-tissue anatomic locations on each scan, and the location of these sites was kept identical on each scan pair. Data were analyzed to evaluate Hounsfield unit differences between these scanners.
  
  
  RESULTS
  In general, there was a low consistency in the Hounsfield unit measurements for each of these sites on scans obtained by the two scanners, with the subcutaneous fat in the left posterolateral flank showing the lowest correlation (intraclass correlation coefficient, 0.198). There were differences in the Hounsfield unit measurements obtained in all anatomic sites on scans obtained by both scanners. Mean Hounsfield unit measurements obtained on the Definition AS Plus scanner were lower than those obtained on the Volume CT scanner, with the intriguing exception of the anterior midline subcutaneous fat Hounsfield unit measurements, which were higher on the Definition AS Plus scanner. All differences were statistically significant (p < 0.05).
  
  
  CONCLUSIONS
  Hounsfield unit measurements for unenhanced abdominal soft tissues of the same patient vary between scanners of two common MDCT manufacturers.
authors.affiliation: 1 Department of Radiology, University of California Davis Health System, 4860 Y St, Ste 3100, Sacramento, CA 95817.
authors.forename: Ramit
authors.initials: R
authors.lastname: Lamba
authors.forename: John P
authors.initials: JP
authors.lastname: McGahan
authors.forename: Michael T
authors.initials: MT
authors.lastname: Corwin
authors.forename: Chin-Shang
authors.initials: CS
authors.lastname: Li
authors.forename: Tien
authors.initials: T
authors.lastname: Tran
authors.forename: J Anthony
authors.initials: JA
authors.lastname: Seibert
authors.forename: John M
authors.initials: JM
authors.lastname: Boone
mesh_terms: D065638:Absorption, Radiation; D000368:Aged; D003238:Connective Tissue / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D003287:Contrast Media; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005260:Female; D006801:Humans; D008297:Male; D061330:Multidetector Computed Tomography / Q000295:instrumentation* / Q000706:statistics & numerical data*; D011860:Radiography, Abdominal / Q000295:instrumentation* / Q000706:statistics & numerical data*
chemical_list: D003287:Contrast Media
keywords: Hounsfield numbers; MDCT