title: Calibrated bold fMRI with an optimized ASL-BOLD dual-acquisition sequence.
abstract: Calibrated fMRI techniques estimate task-induced changes in the cerebral metabolic rate of oxygen (CMRO2) based on simultaneous measurements of cerebral blood flow (CBF) and blood-oxygen-level-dependent (BOLD) signal changes evoked by stimulation. To determine the calibration factor M (corresponding to the maximum possible BOLD signal increase), BOLD signal and CBF are measured in response to a gas breathing challenge (usually CO2or O2). Here we describe an ASL dual-acquisition sequence that combines a background-suppressed 3D-GRASE readout with 2D multi-slice EPI. The concatenation of these two imaging sequences allowed separate optimization of the acquisition for CBF and BOLD data. The dual-acquisition sequence was validated by comparison to an ASL sequence with a dual-echo EPI readout, using a visual fMRI paradigm. Results showed a 3-fold increase in temporal signal-to-noise ratio (tSNR) of the ASL time-series data while BOLD tSNR was similar to that obtained with the dual-echo sequence. The longer TR of the proposed dual-acquisition sequence, however, resulted in slightly lower T-scores (by 30%) in the BOLD activation maps. Further, the potential of the dual-acquisition sequence for M-mapping on the basis of a hypercapnia gas breathing challenge and for quantification of CMRO2changes in response to a motor activation task was assessed. In five subjects, an average gray matter M-value of 8.71±1.03 and fractional changes of CMRO2of 12.5±5% were found. The new sequence remedies the deficiencies of prior combined BOLD-ASL acquisition strategies by substantially enhancing perfusion tSNR, which is essential for accurate BOLD calibration.
authors: Department of Radiology, University of Navarra Hospital, Pamplona, Spain. Electronic address: mfseara@unav.es.
authors: María A
authors: MA
authors: Fernández-Seara
authors: Laboratory for Structural, Physiologic and Functional Imaging, Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, PA, USA.
authors: Zachary B
authors: ZB
authors: Rodgers
authors: Laboratory for Structural, Physiologic and Functional Imaging, Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, PA, USA.
authors: Erin K
authors: EK
authors: Englund
authors: Laboratory for Structural, Physiologic and Functional Imaging, Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, PA, USA.
authors: Felix W
authors: FW
authors: Wehrli
mesh_terms: D000328:Adult; D002138:Calibration; D002560:Cerebrovascular Circulation / Q000502:physiology*; D017352:Echo-Planar Imaging / Q000379:methods; D005260:Female; D066128:Gray Matter / Q000000981:diagnostic imaging*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010100:Oxygen / Q000097:blood*; D059629:Signal-To-Noise Ratio; D013113:Spin Labels; D055815:Young Adult
chemical_list: D013113:Spin Labels; D010100:Oxygen
keywords: 3D GRASE; Arterial spin labeling; Background suppression; CMRO(2) quantification; Calibrated BOLD; Dual-echo EPI