title: High-definition CT Gemstone spectral imaging of the brain: initial results of selecting optimal monochromatic image for beam-hardening artifacts and image noise reduction.
abstract: OBJECTIVE
  The purpose of this study was to select the optimal monochromatic level for gemstone spectral imaging (GSI) to minimize both the image noise and beam-hardening artifacts (BHAs) in nonenhanced cranial computed tomography (CT).
  
  
  METHODS
  One hundred subjects scanned with GSI mode on Discovery CT750HD were enrolled. Six sets of CT images were obtained from a single GSI acquisition: conventional 140 kilovolt (peak) (kV[p]) polychromatic images and 5 sets of monochromatic images (80, 75, 70, 65, and 60 kiloelectron volts [keV]). The background noise in the corona and the BHA in 4 different anatomic regions (medulla oblongata, cerebellar, pons, and the inferior part of frontal lobes) were measured and compared between the polychromatic and monochromatic images. Beam-hardening artifact is defined as the square root of the squared noise difference between the region of interest and background.
  
  
  RESULTS
  The background noise with the monochromatic sets reduced by -36%, -11%, 11%, 10%, and -14%, respectively, compared to the polychromatic image. For BHA, the reductions were 73%, 91%, 92%, and 80%; 53%, 75%, 65%, and 41.%; 27%, 59%, 44%, and 26%; 7%, 46%, 25%, and 20%; and -14%, 33%, 6%, and 19% for the 4 regions of interest. Both the 70 and 65 keV sets had positive background noise reduction (P = 0.285) and BHA reduction with 70 keV were statistically higher (P < 0.05).
  
  
  CONCLUSIONS
  In the nonenhanced cranial CT with GSI, the optimal monochromatic level was determined at 70 keV to provide both image noise reduction (11%) and BHA reduction compared to the conventional polychromatic images.
authors.affiliation: Shanghai Jiaotong University School of Medicine, Department of Radiology, Ruijin Hospital, Shanghai, China.
authors.forename: Xiao Zhu
authors.initials: XZ
authors.lastname: Lin
authors.forename: Fei
authors.initials: F
authors.lastname: Miao
authors.forename: Jian Ying
authors.initials: JY
authors.lastname: Li
authors.forename: Hai Peng
authors.initials: HP
authors.lastname: Dong
authors.forename: Yun
authors.initials: Y
authors.lastname: Shen
authors.forename: Ke Min
authors.initials: KM
authors.lastname: Chen
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000295:instrumentation* / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000295:instrumentation* / Q000379:methods*; D055815:Young Adult