title: Doppler investigation of within-session reproducibility in a visual stimulation task to assess the volunteer-dependent variation.
abstract: OBJECTIVE
  In functional magnetic resonance imaging (MRI) studies in humans the tightness of activity-flow coupling was questioned due to a notable within-session variability of the signals obtained. To differentiate between moments of volunteer-dependent or technique-inherent variation in hemodynamic MRI measurements a method with a low technique-inherent variation is needed. Therefore, and because temporal features might also be of some relevance, we used the transcranial Doppler method.
  
  
  METHODS
  In 22 healthy volunteers the flow-velocity response to a visual stimulation task was evaluated. Conditions of 20 s of eye closure were altered with 40 s of silent reading, repeated 10 times. Averaged individual flow-velocity responses were evaluated from conditions of 40 s of stimulation and a 5-second time interval prior to the beginning of stimulation. The averaged data were subtracted from each single recording to calculate the mean squared differences (MSD). Statistical evaluation was performed according to a two-way ANOVA for repeated measures. To obtain additional qualitative data of the flow response, the individual flow curves were evaluated according to a control system approach specifying a second-order linear model.
  
  
  RESULTS
  The coefficient of variation (COV) of the within-session MSD was 7% for the stimulation phase and 2.9% for the resting phase, whereas the respective COVs were 15 and 8.1% for the interindividual MSDs. The interindividual COVs of control system parameters ranged from 3.6 to 7.6%. The ANOVA resulted in a significant (p < 0.003) difference for the MSD values between stimulation conditions, whereas the test repetition (p = 0.55) and the test for an interaction of repetition and stimulation condition (p = 0.54) revealed no significance.
  
  
  CONCLUSIONS
  Confirming the notion of a tight coupling between cortical activity and cerebral blood flow and being indicative of a low technique-inherent variation, we found a high within-session reproducibility in a functional Doppler test.
authors.affiliation: Department of Neurology, Faculty of Medicine, Justus Liebig University of Giessen, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Rosengarten
authors.forename: S
authors.initials: S
authors.lastname: Osthaus
authors.forename: M
authors.initials: M
authors.lastname: Kaps
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001794:Blood Pressure / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006801:Humans; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D008297:Male; D010775:Photic Stimulation; D017585:Ultrasonography, Doppler, Transcranial