title: RF excitation profiles with FAIR: impact of truncation of the arterial input function on quantitative perfusion.
abstract: This study investigates the impact of imaging coil length and consequent truncation of the arterial input function on the perfusion signal contrast obtained in the flow-sensitive alternating inversion recovery (FAIR) perfusion imaging measurement. We examined the difference in perfusion contrast achieved with head, head and neck, and body imaging coils based on the hypothesis that the standard head coil provides a truncated input function compared with that provided by the body coil and that this effect will be accentuated at long inversion times. The TI-dependent cerebral response of the FAIR sequence was examined at 1.5 T by varying the TI from 200 to 3500 msec with both the head and whole body coils (n = 5) as well as using a head and neck coil (n = 3). Difference signal intensity DeltaM and quantitative cerebral blood flow (CBF) were plotted against TI for each coil configuration. Despite a lower signal-to-noise ratio, relative CBF was significantly greater when measured with the body or head and neck coil compared with the standard head coil for longer inversion times (two-way ANOVA, P < or = 0.002). This effect is attributed to truncation of the arterial input function of labeled water by the standard head coil and the resultant inflow of unlabeled spins to the image slice during control image acquisition, resulting in overestimation of CBF. The results support the conclusion that the arterial input function depends on the anatomic extent of the inversion pulse in FAIR, particularly at longer mixing times (TI > 1200 msec at 1.5 T). Use of a head and neck coil ensures adequate inversion while preserving SNR that is lost in the body coil.
authors.affiliation: Department of Radiology, Albert Einstein College of Medicine and Montefiore Medical Center, Bronx, New York 10467, USA. lipton@nki.rfmh.org
authors.forename: M L
authors.initials: ML
authors.lastname: Lipton
authors.forename: C A
authors.initials: CA
authors.lastname: Branch
authors.forename: J
authors.initials: J
authors.lastname: Hrabe
authors.forename: D P
authors.initials: DP
authors.lastname: Lewis
authors.forename: J A
authors.initials: JA
authors.lastname: Helpern
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D001921:Brain / Q000098:blood supply*; D002545:Brain Ischemia / Q000175:diagnosis* / Q000503:physiopathology; D004867:Equipment Design; D006801:Humans; D007089:Image Enhancement / Q000295:instrumentation*; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation*; D007231:Infant, Newborn; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008297:Male; D012016:Reference Values; D012039:Regional Blood Flow / Q000502:physiology; D012680:Sensitivity and Specificity