title: fMRI contrast at high and ultrahigh magnetic fields: insight from complementary methods.
abstract: This manuscript examines the origins and nature of the function-derived activation detected by magnetic resonance imaging at ultrahigh fields using different encoding methods. A series of preclinical high field (7 T) and ultra-high field (17.2 T) fMRI experiments were performed using gradient echo EPI, spin echo EPI and spatio-temporally encoded (SPEN) strategies. The dependencies of the fMRI signal change on the strength of the magnetic field and on different acquisition and sequence parameters were investigated. Artifact-free rat brain images with good resolution in all areas, as well as significant localized activation maps upon forepaw stimulation, were obtained in a single scan using fully refocused SPEN sequences devoid of T2* effects. Our results showed that, besides the normal T2-weighted BOLD contribution that arises in spin-echo sequences, fMRI SPEN signals contain a strong component caused by apparent T1-related effects, demonstrating the potential of such technique for exploring functional activation in rodents and on humans at ultrahigh fields.
authors: NeuroSpin, Commissariat à l'Energie Atomique et aux Energies Alternatives, Gif-sur-Yvette, France.
authors: Luisa
authors: L
authors: Ciobanu
authors: Weizmann Institute of Science, Rehovot, Israel.
authors: Eddy
authors: E
authors: Solomon
authors: NeuroSpin, Commissariat à l'Energie Atomique et aux Energies Alternatives, Gif-sur-Yvette, France.
authors: Nadya
authors: N
authors: Pyatigorskaya
authors: Weizmann Institute of Science, Rehovot, Israel.
authors: Tangi
authors: T
authors: Roussel
authors: NeuroSpin, Commissariat à l'Energie Atomique et aux Energies Alternatives, Gif-sur-Yvette, France.
authors: Denis
authors: D
authors: Le Bihan
authors: Weizmann Institute of Science, Rehovot, Israel. Electronic address: lucio.frydman@weizmann.ac.il.
authors: Lucio
authors: L
authors: Frydman
mesh_terms: D000465:Algorithms; D000818:Animals; D016477:Artifacts; D001931:Brain Mapping; D017352:Echo-Planar Imaging; D004558:Electric Stimulation; D004574:Electromagnetic Fields; D005552:Forelimb / Q000294:innervation / Q000502:physiology; D018496:Hyperoxia / Q000523:psychology; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010100:Oxygen / Q000097:blood; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D010100:Oxygen
keywords: BOLD activation; Forepaw stimulation; Functional MRI; Spatiotemporal encoding; T1 contrast; Ultrahigh fields