title: Quantifying the effect of repetitive transcranial magnetic stimulation in the rat brain by μSPECT CBF scans.
abstract: BACKGROUND
  Repetitive transcranial magnetic stimulation (rTMS) is used to treat neurological and psychiatric disorders such as depression and addiction amongst others. Neuro-imaging by means of SPECT is a non-invasive manner of evaluating regional cerebral blood flow (rCBF) changes, which are assumed to reflect changes in neural activity.
  
  
  OBJECTIVE
  rCBF changes induced by rTMS are evaluated by comparing stimulation on/off in different stimulation paradigms using microSPECT of the rat brain.
  
  
  METHODS
  Rats (n = 6) were injected with 10 mCi of (99m)Tc-HMPAO during application of two rTMS paradigms (1 Hz and 10 Hz, 1430 A at each wing of a 20 mm figure-of-eight coil) and sham. SPM- and VOI-based analysis was performed.
  
  
  RESULTS
  rTMS caused widespread significant hypoperfusion throughout the entire rat brain. Differences in spatial extent and intensity of hypoperfusion were observed between both stimulation paradigms: 1 Hz caused significant hypoperfusion (P < 0.05) in 11.9% of rat brain volume while 10 Hz caused this in 23.5%; the minimal t-value induced by 1 Hz was -24.77 while this was -17.98 due to 10 Hz. Maximal percentage of hypoperfused volume due to 1 Hz and 10 Hz was reached at tissue experiencing 0.03-0.15 V/m.
  
  
  CONCLUSIONS
  High-frequency (10 Hz) stimulation causes more widespread hypoperfusion, while 1 Hz induces more pronounced hypoperfusion. The effect of rTMS is highly dependent on the electric field strength in the brain tissue induced by the TMS coil. This innovative imaging approach can be used as a fast screening tool in quantifying and evaluating the effect of various stimulation paradigms and coil designs for TMS and offers a means for research and development.
authors.affiliation: Molecular Imaging Center Antwerp (MICA), Universiteitsplein 1, 2610 Wilrijk, University of Antwerp, Antwerp, Belgium. Tine.Wyckhuys@ua.ac.be
authors.forename: Tine
authors.initials: T
authors.lastname: Wyckhuys
authors.forename: Nele
authors.initials: N
authors.lastname: De Geeter
authors.forename: Guillaume
authors.initials: G
authors.lastname: Crevecoeur
authors.forename: Sigrid
authors.initials: S
authors.lastname: Stroobants
authors.forename: Steven
authors.initials: S
authors.lastname: Staelens
mesh_terms: D000818:Animals; D001921:Brain / Q000098:blood supply / Q000000981:diagnostic imaging*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D008297:Male; D011877:Radionuclide Imaging; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D050781:Transcranial Magnetic Stimulation
keywords: (99m)Tc-HMPAO; Electric field distribution; Regional cerebral blood flow; Repetitive transcranial magnetic stimulation; μSPECT