title: Spectral detector CT-derived virtual non-contrast images: comparison of attenuation values with unenhanced CT.
abstract: To assess virtual non-contrast (VNC) images obtained on a detection-based spectral detector CT scanner and determine how attenuation on VNC images derived from various phases of enhanced CT compare to those obtained from true unenhanced images.
  
  
  
  In this HIPAA compliant, IRB approved prospective multi-institutional study, 46 patients underwent pre- and post-contrast imaging on a prototype dual-layer spectral detector CT between October 2013 and November 2015, yielding 84 unenhanced and VNC pairs (25 arterial, 39 portal venous/nephrographic, 20 urographic). Mean attenuation was measured by one of three readers in the liver, spleen, kidneys, psoas muscle, abdominal aorta, and subcutaneous fat. Equivalence testing was used to determine if the mean difference between unenhanced and VNC attenuation was less than 5, 10, or 15 HU. VNC image quality was assessed on a 5 point scale.
  
  
  
  Mean difference between unenhanced and VNC attenuation was <15 HU in 92.6%, <10 HU in 75.2%, and <5 HU in 44.4% of all measurements. Unenhanced and VNC attenuation were equivalent in all tissues except fat using a threshold of <10 HU difference (p < 0.05). No significant variation was seen between phases. In fat, VNC overestimated the HU relative to unenhanced images. VNC image quality was rated as excellent or good in 84% of arterial phase and 85% of nephrographic phase cases, but only 40% of urographic phase.
  
  
  
  VNC images derived from novel dual layer spectral detector CT demonstrate attenuation values similar to unenhanced images in all tissues evaluated except for subcutaneous fat. Further study is needed to determine if attenuation thresholds currently used clinically for common pathology should be adjusted, particularly for lesions containing fat.
authors.affiliation: Department of Radiology, UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, 75390-9178, USA. Lakshmi.Ananthakrishnan@utsouthwestern.edu.|UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, 75390-9178, USA. Lakshmi.Ananthakrishnan@utsouthwestern.edu.
authors.forename: Lakshmi
authors.identifier: 0000-0001-8597-9964
authors.initials: L
authors.lastname: Ananthakrishnan
authors.affiliation: UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, 75390-9178, USA.
authors.forename: Prabhakar
authors.initials: P
authors.lastname: Rajiah
authors.affiliation: UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, 75390-9178, USA.
authors.forename: Richard
authors.initials: R
authors.lastname: Ahn
authors.affiliation: University Hospitals Cleveland Medical Center, 11100 Euclid Avenue, Cleveland, OH, 44106, USA.
authors.forename: Negin
authors.initials: N
authors.lastname: Rassouli
authors.affiliation: UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, 75390-9178, USA.
authors.forename: Yin
authors.initials: Y
authors.lastname: Xi
authors.affiliation: UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, 75390-9178, USA.
authors.forename: Todd C
authors.initials: TC
authors.lastname: Soesbe
authors.affiliation: UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, 75390-9178, USA.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Lewis
authors.affiliation: UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, 75390-9178, USA.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Lenkinski
authors.affiliation: UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, 75390-9178, USA.
authors.forename: John R
authors.initials: JR
authors.lastname: Leyendecker
authors.affiliation: UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX, 75390-9178, USA.
authors.forename: Suhny
authors.initials: S
authors.lastname: Abbara
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011857:Radiographic Image Interpretation, Computer-Assisted; D011860:Radiography, Abdominal / Q000379:methods*; D015900:Radiography, Dual-Energy Scanned Projection / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: Dual energy; Dual layer detector; SDCT; Spectral detector CT; Unenhanced versus VNC; VNC; VNC attenuation; Virtual non-contrast