title: Test-retest variability and reliability of 123I-IBZM SPECT measurement of striatal dopamine D2 receptor availability in healthy volunteers and influence of iterative reconstruction algorithms.
abstract: OBJECTIVE
  123I-IBZM single photon emission computed tomography (SPECT) is a widely used method to measure D(2) receptor availability. However, test-retest variability and reliability have not been reported yet. This study aimed to further characterize 123I-IBZM SPECT in healthy volunteers (HVs), by assessing (1) pseudoequilibrium interval after bolus injection; (2) normal specific uptake ratio (SUR) values using filtered-backprojection (FBP); and the iterative reconstruction algorithm ordered-subsets expectation maximization (OSEM); (3) test-retest variability and reliability (intraclass correlation coefficient); and (4) influence of OSEM on test-retest variability and reliability.
  
  
  METHODS
  Ten HVs (Group A) were scanned twice 48 h apart for test-retest variability and reliability measurements, and n = 4 of them were sequentially scanned over time. Eighteen HVs (Group B) were scanned once at pseudoequilibrium. For reconstruction FBP was used. Test-retest scans were reconstructed in addition using OSEM. SPECT-MRI coregistration was used for region of interest drawing.
  
  
  RESULTS
  Pseudoequilibrium was achieved at 90 min postinjection (p.i.) and maintained until the end of the SPECT session (n = 4), and mean SUR at this time point was 0.96 +/- 0.14 (Groups A + B, n = 28). Mean SUR at test was 0.96 +/- 0.19 and at retest 0.94 +/- 0.19 (Group A, n = 10). Using FBP, test-retest variability was (12.7 +/- 9.6)% and reliability was 0.74. Using OSEM with 18 equivalent iterations, test-retest variability and reliability were improved to (6.5 +/- 5.2)% and 0.84, respectively.
  
  
  CONCLUSIONS
  123I-IBZM SPECT imaging using the bolus injection and a single scan at 90 min p.i. is a reproducible method showing acceptable test-retest variability and reliability. Test-retest variability and reliability can be substantially improved using OSEM with 12-36 equivalent iterations.
authors.affiliation: Experimental Medicine, Clinical Pharmacology Discovery Medicine, Psychiatry Centre of Excellence for Drug Discovery, GlaxoSmithKline, Barcelona, Spain. ana.m.catafau@gsk.com
authors.forename: Ana M
authors.initials: AM
authors.lastname: Catafau
authors.forename: Santiago
authors.initials: S
authors.lastname: Bullich
authors.forename: Mónica
authors.initials: M
authors.lastname: Danús
authors.forename: María M
authors.initials: MM
authors.lastname: Penengo
authors.forename: Albert
authors.initials: A
authors.lastname: Cot
authors.forename: Sergio
authors.initials: S
authors.lastname: Abanades
authors.forename: Magí
authors.initials: M
authors.lastname: Farré
authors.forename: Javier
authors.initials: J
authors.lastname: Pavía
authors.forename: Domènec
authors.initials: D
authors.lastname: Ros
mesh_terms: D000328:Adult; D000465:Algorithms; D001549:Benzamides / Q000493:pharmacokinetics*; D003287:Contrast Media / Q000493:pharmacokinetics*; D003342:Corpus Striatum / Q000378:metabolism*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics; D008297:Male; D008875:Middle Aged; D011759:Pyrrolidines / Q000493:pharmacokinetics*; D017448:Receptors, Dopamine D2 / Q000378:metabolism*; D015203:Reproducibility of Results; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
chemical_list: D001549:Benzamides; D003287:Contrast Media; D007457:Iodine Radioisotopes; D011759:Pyrrolidines; D017448:Receptors, Dopamine D2; C055743:3-iodo-2-hydroxy-6-methoxy-N-((1-ethyl-2-pyrrolidinyl)methyl)benzamide