title: Attenuation correction of SPECT images based on separately performed CT: Effect on the measurement of regional uptake values.
abstract: OBJECTIVE
  A new software approach uses separately acquired CT images for attenuation correction after retrospective fusion with the SPECT data. This study evaluates the effect of this CT-based attenuation correction on indium-111-pentetreotide-SPECT images.
  
  
  METHODS
  Indium-111-pentetreotide-SPECT imaging using a dual-head gamma camera e.cam (Siemens Medical Solutions, Erlangen, Germany) as well as separate spiral computed tomography (CT) was performed in 13 patients. After fusion of SPECT and CT data, the bilinear attenuation coefficients were calculated for each pixel in the CT image volume using their Hounsfield unit values and attenuation-corrected images were reconstructed iteratively (OSEM 2D). Regions of interest (ROIs) were drawn on 24 suspicious foci and background, and target to background ratios were calculated for corrected (TBAC) and uncorrected (TBNAC) images. The shortest distance from the centre of the lesion to the surface of the body (DS) was measured on the corresponding CT slice. Furthermore, ROIs were drawn over the rim and the centre of the liver. Ratios of hepatic count rates for corrected (LRAC) and uncorrected (LRNAC) images were also compared.
  
  
  RESULTS
  In lesions located more centrally, TBAC was up to 52% higher, whereas in peripherally located lesions, TBAC was up to 63% lower than TBNAC. The TBAC/TBNAC quotient was linearly correlated with DS. In the liver, attenuation correction resulted in a 35% increase of LRAC compared with LRNAC.
  
  
  CONCLUSIONS
  Attenuation correction of SPECT images performed by separately acquired CT data is quick and simple. It improves the contrast between target and background for lesions located more centrally in the body and improves homogeneity of the visualisation of tracer uptake in the liver.
authors.affiliation: Nuklearmedizinische Klinik, Universität Erlangen-Nürnberg, Krankenhausstr. 12, 91054 Erlangen. wolfgang.roemer@nuklear.imed.uni-erlangen.de
authors.forename: W
authors.initials: W
authors.lastname: Römer
authors.forename: E
authors.initials: E
authors.lastname: Fiedler
authors.forename: M
authors.initials: M
authors.lastname: Pavel
authors.forename: A
authors.initials: A
authors.lastname: Pfahlberg
authors.forename: T
authors.initials: T
authors.lastname: Hothorn
authors.forename: H
authors.initials: H
authors.lastname: Herzog
authors.forename: W
authors.initials: W
authors.lastname: Bautz
authors.forename: T
authors.initials: T
authors.lastname: Kuwert
mesh_terms: D000328:Adult; D000368:Aged; D001692:Biological Transport; D006801:Humans; D007205:Indium Radioisotopes / Q000493:pharmacokinetics*; D008875:Middle Aged; D009369:Neoplasms / Q000000981:diagnostic imaging*; D018358:Neuroendocrine Tumors / Q000000981:diagnostic imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D015899:Tomography, Emission-Computed, Single-Photon / Q000592:standards*; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D007205:Indium Radioisotopes; D019275:Radiopharmaceuticals