title: Quantifying hemodynamic refractory bold effects in normal subjects at the single-subject level using an inverse logit fitting procedure.
abstract: OBJECTIVE
  To evaluate whether hemodynamic refractory effects provoked by repeated visual stimulation can be detected and quantified at the single-subject level using a recently described hemodynamic response function (HRF) fitting algorithm.
  
  
  METHODS
  Hemodynamic refractory effects were induced with an easily applicable functional MRI (fMRI) paradigm. A fitting method with inverse logit (IL) functions was applied to quantify net HRFs at the single-subject level with three interstimulus intervals (ISI; 1, 2, and 6 s). The model yielded amplitude, latencies, and width for each HRF.
  
  
  RESULTS
  HRF fitting was possible in 44 of 51 healthy volunteers, with excellent goodness-of-fit (R(2) = 0.9745 ± 0.0241). Refractory effects were most pronounced for the 1-s ISI (P < 0.001) and had nearly disappeared for the 6-s ISI.
  
  
  CONCLUSIONS
  Quantifying refractory effects in individuals was possible in 86.3% of normal subjects using the IL fitting algorithm. This setup may be suitable to explore such effects in individual patients.
authors: Department of Radiology and Nuclear Medicine, Ghent University, Ghent, Belgium. benedicte.descamps@ugent.be
authors: Benedicte
authors: B
authors: Descamps
authors: Pieter
authors: P
authors: Vandemaele
authors: Harmen
authors: H
authors: Reyngoudt
authors: Karel
authors: K
authors: Deblaere
authors: Luc
authors: L
authors: Leybaert
authors: Koen
authors: K
authors: Paemeleire
authors: Eric
authors: E
authors: Achten
mesh_terms: D000328:Adult; D000465:Algorithms; D000704:Analysis of Variance; D001931:Brain Mapping / Q000379:methods*; D005260:Female; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010775:Photic Stimulation; D012016:Reference Values