title: Spectral optimization of iodine-enhanced CT: Quantifying the effect of tube voltage on image quality and radiation exposure determined at an anthropomorphic phantom.
abstract: OBJECTIVE
  To provide an experimental basis for spectral optimization of iodine-enhanced CT by a quantitative analysis of image quality and radiation dose characteristics consistently measured for a large variety of scan settings at an anthropomorphic phantom.
  
  
  METHODS
  CT imaging and thermoluminescent dosimetry were performed at an anthropomorphic whole-body phantom with iodine inserts for different tube voltages (U, 70-140kV) and current-time products (Q, 60-300mAs). For all U-Q combinations, the iodine contrast (C), the noise level (N) and, from these, the contrast-to-noise ratio (CNR) of reconstructed CT images were determined and parameterized as a function of U, Q or the measured absorbed dose (D). Finally, two characteristic curves were derived that give the relative increase of CNR at constant D and the relative decrease of D at constant CNR when lowering U.
  
  
  RESULTS
  Lowering U affects the measured CNR only slightly but markedly reduces D. For example, reducing U from 120kV to 70kV increases the CNR at constant D by a factor of nearly 1.8 or, alternatively, reduces D at constant CNR by a factor of nearly 5.
  
  
  CONCLUSIONS
  Spectral optimization by lowering U is an effective approach to attain the necessary CNR for a specific diagnostic task at hand while at the same time reducing radiation exposure as far as practically achievable. The characteristic curves derived in this study from extensive measurements at a reference 'person' can support CT users in an easy-to-use manner to select an appropriate voltage for various clinical scenarios.
authors.affiliation: Department of Medical and Occupational Radiation Protection, Federal Office for Radiation Protection, Oberschleissheim, Germany. Electronic address: gbrix@bfs.de.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Brix
authors.affiliation: Department of Medical and Occupational Radiation Protection, Federal Office for Radiation Protection, Oberschleissheim, Germany.
authors.forename: Ursula
authors.initials: U
authors.lastname: Lechel
authors.affiliation: Institute of Clinical Radiology and Nuclear Medicine, University Medical Center Mannheim, University of Heidelberg, Mannheim, Germany.
authors.forename: Sonja
authors.initials: S
authors.lastname: Sudarski
authors.affiliation: Department of Clinical Radiology, Grosshadern Clinic, Hospital of the Ludwig-Maximilians University, Munich, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Trumm
authors.affiliation: Institute of Clinical Radiology and Nuclear Medicine, University Medical Center Mannheim, University of Heidelberg, Mannheim, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Henzler
mesh_terms: D006801:Humans; D007455:Iodine; D019047:Phantoms, Imaging; D011785:Quality Assurance, Health Care; D000069079:Radiation Exposure / Q000032:analysis*; D059629:Signal-To-Noise Ratio; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*
chemical_list: D007455:Iodine
keywords: Contrast-enhanced CT; Image quality; Patient exposure; Spectral optimization