title: Quantitative spectral K-edge imaging in preclinical photon-counting x-ray computed tomography.
abstract: OBJECTIVE
  The objective of this study was to investigate the feasibility and the accuracy of spectral computed tomography (spectral CT) to determine the tissue concentrations and localization of high-attenuation, iodine-based contrast agents in mice. Iodine tissue concentrations determined with spectral CT are compared with concentrations measured with single-photon emission computed tomography (SPECT) and inductively coupled plasma mass spectrometry (ICP-MS).
  
  
  METHODS
  All animal procedures were performed according to the US National Institutes of Health principles of laboratory animal care and were approved by the ethical review committee of Maastricht, The Netherlands. Healthy Swiss mice (n = 4) were injected with an iodinated emulsion radiolabeled with indium as multimodal contrast agent for CT and SPECT. The CT and SPECT scans were acquired using a dedicated small-animal SPECT/CT system. Subsequently, scans were performed with a preclinical spectral CT scanner equipped with a photon-counting detector and 6 energy threshold levels. Quantitative data analysis of SPECT and spectral CT scans were obtained using 3-dimensional volumes-of-interest drawing methods. The ICP-MS on dissected organs was performed to determine iodine uptake per organ and was compared with the amounts determined from spectral CT and SPECT.
  
  
  RESULTS
  Iodine concentrations obtained with image-processed spectral CT data correlated well with data obtained either with noninvasive SPECT imaging (slope = 0.96, r = 0.75) or with ICP-MS (slope = 0.99, r = 0.89) in tissue samples.
  
  
  CONCLUSIONS
  This preclinical proof-of-concept study shows the in vivo quantification of iodine concentrations in tissues using spectral CT. Our multimodal imaging approach with spectral CT and SPECT using radiolabeled iodinated emulsions together with ICP-based quantification allows a direct comparison of all methods. Benchmarked against ICP-MS data, spectral CT in the present implementation shows a slight underestimation of organ iodine concentrations compared with SPECT but with a more narrow distribution. This slight deviation is most likely caused by experimental rather than technical issues.
authors.affiliation: From the *Department of Medical Physics, Catharina Hospital; †Department of Biomedical Engineering, Biomedical NMR, Eindhoven University of Technology, Eindhoven, The Netherlands; ‡Philips Research Europe, Hamburg, Germany; and §Philips Research Europe, Eindhoven, The Netherlands.
authors.forename: Anke
authors.initials: A
authors.lastname: de Vries
authors.forename: Ewald
authors.initials: E
authors.lastname: Roessl
authors.forename: Esther
authors.initials: E
authors.lastname: Kneepkens
authors.forename: Axel
authors.initials: A
authors.lastname: Thran
authors.forename: Bernhard
authors.initials: B
authors.lastname: Brendel
authors.forename: Gerhard
authors.initials: G
authors.lastname: Martens
authors.forename: Roland
authors.initials: R
authors.lastname: Proska
authors.forename: Klaas
authors.initials: K
authors.lastname: Nicolay
authors.forename: Holger
authors.initials: H
authors.lastname: Grüll
mesh_terms: D000818:Animals; D003287:Contrast Media / Q000493:pharmacokinetics*; D005240:Feasibility Studies; D021621:Imaging, Three-Dimensional; D007205:Indium Radioisotopes / Q000493:pharmacokinetics*; D007455:Iodine; D051379:Mice; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D013054:Spectrophotometry, Atomic; D015899:Tomography, Emission-Computed, Single-Photon; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D003287:Contrast Media; D007205:Indium Radioisotopes; D007455:Iodine