Assessment of quantification accuracy and image quality of a full-body dual-layer spectral CT system

J Appl Clin Med Phys. 2018 Jan;19(1):204-217. doi: 10.1002/acm2.12243. Epub 2017 Dec 20.


The performance of a recently introduced spectral computed tomography system based on a dual-layer detector has been investigated. A semi-anthropomorphic abdomen phantom for CT performance evaluation was imaged on the dual-layer spectral CT at different radiation exposure levels (CTDIvol of 10 mGy, 20 mGy and 30 mGy). The phantom was equipped with specific low-contrast and tissue-equivalent inserts including water-, adipose-, muscle-, liver-, bone-like materials and a variation in iodine concentrations. Additionally, the phantom size was varied using different extension rings to simulate different patient sizes. Contrast-to-noise (CNR) ratio over the range of available virtual mono-energetic images (VMI) and the quantitative accuracy of VMI Hounsfield Units (HU), effective-Z maps and iodine concentrations have been evaluated. Central and peripheral locations in the field-of-view have been examined. For all evaluated imaging tasks the results are within the calculated theoretical range of the tissue-equivalent inserts. Especially at low energies, the CNR in VMIs could be boosted by up to 330% with respect to conventional images using iDose/spectral reconstructions at level 0. The mean bias found in effective-Z maps and iodine concentrations averaged over all exposure levels and phantom sizes was 1.9% (eff. Z) and 3.4% (iodine). Only small variations were observed with increasing phantom size (+3%) while the bias was nearly independent of the exposure level (±0.2%). Therefore, dual-layer detector based CT offers high quantitative accuracy of spectral images over the complete field-of-view without any compromise in radiation dose or diagnostic image quality.

Keywords: dual-energy CT; effective atomic number; iodine quantification; spectral CT; virtual mono-energetic imaging.

MeSH terms

  • Humans
  • Image Processing, Computer-Assisted / methods
  • Phantoms, Imaging*
  • Quality Assurance, Health Care / standards*
  • Radiation Dosage
  • Radiation Protection / instrumentation
  • Radiation Protection / methods*
  • Radiography, Dual-Energy Scanned Projection / instrumentation*
  • Radiography, Dual-Energy Scanned Projection / methods*
  • Tomography, X-Ray Computed / instrumentation
  • Tomography, X-Ray Computed / methods*
  • Whole Body Imaging / methods*