High-definition CT Gemstone spectral imaging of the brain: initial results of selecting optimal monochromatic image for beam-hardening artifacts and image noise reduction

J Comput Assist Tomogr. Mar-Apr 2011;35(2):294-7. doi: 10.1097/RCT.0b013e3182058d5c.


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).

Materials and 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).

Conclusion: 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.

Publication types

  • Evaluation Study

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Algorithms*
  • Artifacts*
  • Brain / diagnostic imaging*
  • Female
  • Humans
  • Image Enhancement / instrumentation*
  • Image Enhancement / methods*
  • Male
  • Middle Aged
  • Pilot Projects
  • Reproducibility of Results
  • Sensitivity and Specificity
  • Tomography, X-Ray Computed / instrumentation*
  • Tomography, X-Ray Computed / methods*
  • Young Adult