title: Noninvasive quantification of dopamine D2 receptors with iodine-123-IBF SPECT.
abstract: Iodine-123-iodobenzofuran (IBF) is a potent dopamine D2 receptor ligand suited for quantitative receptor studies. The purpose of this study was to evaluate three noninvasive methods of estimating the receptor parameter k3/k4 in humans with IBF-SPECT.
  
  
  METHODS
  Scans were acquired every 5 min for 180 min using a triple-headed SPECT system following a bolus injection of IBF (296 +/- 37 MBq) in 14 normal volunteers. k3/k4 was estimated by the peak equilibrium ratio (RPE) method and two proposed methods: a variation of the graphic method that derives the ratio of ligand distribution volumes (RV) and area ratio (RA) method, in which the ratio is calculated from the areas under the specific binding and nondisplaceable activity curves.
  
  
  RESULTS
  The mean RPE, RV and RA were 2.74 +/- 0.40, 3.06 +/- 0.42 and 2.26 +/- 0.28, respectively. Both RPE and RA underestimated RV. The relationship between RPE or RA and RV was linear (p < or = 10(-5), RA showed higher correlation (r = 0.94) with RV than did RPE (r = 0.90). Simulations based on a tracer kinetic model showed that RV, unlike RPE or RA, is affected by neither regional cerebral blood flow (rCBF) nor peripheral clearance rate (CR) of IBF. All three measures showed a significant decline with increasing age (r = 0.54-0.58, p < 0.05).
  
  
  CONCLUSIONS
  RV is preferred because it provides a theoretically valid estimate of k3/k4, independently of rCBF or CR. Alternatively, RA might be preferred to RPE because the former is simpler than the latter to implement yet the former provides a measure that equally well correlates with k3/k4.
authors.affiliation: Department of Nuclear Medicine, Mount Sinai Hospital, Toronto, Ontario Canada.
authors.forename: M
authors.initials: M
authors.lastname: Ichise
authors.forename: J R
authors.initials: JR
authors.lastname: Ballinger
authors.forename: H
authors.initials: H
authors.lastname: Golan
authors.forename: D
authors.initials: D
authors.lastname: Vines
authors.forename: A
authors.initials: A
authors.lastname: Luong
authors.forename: S
authors.initials: S
authors.lastname: Tsai
authors.forename: H F
authors.initials: HF
authors.lastname: Kung
mesh_terms: D000328:Adult; D001572:Benzofurans / Q000493:pharmacokinetics; D001921:Brain / Q000000981:diagnostic imaging* / Q000378:metabolism; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007457:Iodine Radioisotopes; D008297:Male; D008954:Models, Biological; D011759:Pyrrolidines / Q000493:pharmacokinetics; D017448:Receptors, Dopamine D2 / Q000032:analysis*; D013997:Time Factors; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D001572:Benzofurans; D007457:Iodine Radioisotopes; D011759:Pyrrolidines; D017448:Receptors, Dopamine D2; C062439:5-iodo-N-((1-ethyl-2-pyrrolidinyl)methyl)-2,3-dihydrobenzofurancarboxamide