title: Exogenous contrast agent improves sensitivity of gradient-echo functional magnetic resonance imaging at 9.4 T.
abstract: Relative to common clinical magnetic field strengths, higher fields benefit functional brain imaging both by providing additional signal for high-resolution applications and by improving the sensitivity of endogenous contrast due to the blood oxygen level dependent (BOLD) mechanism, which has limited detection power at low magnetic fields relative to the use of exogenous contrast agent. This study evaluates the utility of iron oxide contrast agent for gradient echo functional MRI at 9.4 T in rodents using cocaine and methylphenidate as stimuli. Relative to the BOLD method, the use of high iron doses and short echo times provided a roughly twofold global increase in functional sensitivity, while also suppressing large vessel signal and reducing susceptibility artifacts. Furthermore, MRI measurements of the functional percentage change in cerebral blood volume (CBV) showed excellent agreement with results obtained at much lower magnetic field strengths, demonstrating that MRI estimates of this quantity are roughly independent of magnetic field when appropriate techniques are employed. The derived field dependencies for relative sensitivity and MRI estimates of the percentage change in CBV suggest that the benefits provided by exogenous agents will persist even at much higher magnetic fields than 9.4 T.
authors.affiliation: MGH/MIT/HMS Athinoula A Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Boston 02129, USA. jbm@nmr.mgh.harvard.edu
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Mandeville
authors.forename: Bruce G
authors.initials: BG
authors.lastname: Jenkins
authors.forename: Yin-Ching I
authors.initials: YC
authors.lastname: Chen
authors.forename: Ji-Kyung
authors.initials: JK
authors.lastname: Choi
authors.forename: Young R
authors.initials: YR
authors.lastname: Kim
authors.forename: Deniz
authors.initials: D
authors.lastname: Belen
authors.forename: Christina
authors.initials: C
authors.lastname: Liu
authors.forename: Barry E
authors.initials: BE
authors.lastname: Kosofsky
authors.forename: John J A
authors.initials: JJ
authors.lastname: Marota
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D016477:Artifacts; D001921:Brain / Q000187:drug effects*; D002560:Cerebrovascular Circulation; D003042:Cocaine / Q000008:administration & dosage*; D003287:Contrast Media / Q000008:administration & dosage*; D052203:Ferrosoferric Oxide; D007501:Iron / Q000008:administration & dosage*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010087:Oxides / Q000008:administration & dosage*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012680:Sensitivity and Specificity
chemical_list: D003287:Contrast Media; D010087:Oxides; D007501:Iron; D003042:Cocaine; D052203:Ferrosoferric Oxide