title: [The effect of the stimulus frequency, stimulus amplitude and blood pressure on the signal response in functional MRT: studies on an animal model].
abstract: OBJECTIVE
  To examine the influence of frequency and amplitude of a stimulus and the effect of blood pressure on signal intensity changes in functional MRI.
  
  
  METHODS
  Somatosensory stimulation of five (normotonic/hypotonic) anesthetized rats was performed with different stimulus frequencies and amplitudes. Measurements were performed with a 2.4 Tesla experimental scanner using a gradient-echo (GE) echo-planar imaging (EPI) sequence.
  
  
  RESULTS
  The highest signal change was found at a frequency of 3 Hz and a stimulation amplitude of ten times the threshold value. A decrease of blood pressure to half the normotonic value gave rise to a decrease of the neuronal response of about 17%.
  
  
  CONCLUSIONS
  Optimization of the stimulation frequency and stimulation amplitude maximizes signal changes in functional MRI of the somatosensory cortex. Even with a standardized paradigm, variations in measured neuronal activity may occur when blood pressure changes cannot be compensated by autoregulation.
authors.affiliation: Abteilung Neuroradiologie, Universitätsklinikum Heidelberg. eckhard_hempel@med.uni-heidelberg.de
authors.forename: E
authors.initials: E
authors.lastname: Hempel
authors.forename: W
authors.initials: W
authors.lastname: Reith
authors.forename: V
authors.initials: V
authors.lastname: Elste
authors.forename: S
authors.initials: S
authors.lastname: Heiland
authors.forename: K
authors.initials: K
authors.lastname: Sartor
mesh_terms: D000818:Animals; D001794:Blood Pressure; D001921:Brain / Q000033:anatomy & histology*; D004558:Electric Stimulation / Q000295:instrumentation / Q000379:methods; D004566:Electrodes; D005583:Fourier Analysis; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation