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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 CO2 or 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 CMRO2 changes 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 CMRO2 of 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.

SUBMITTER: Fernandez-Seara MA

PROVIDER: S-EPMC5159288 | biostudies-literature | 2016 Nov

REPOSITORIES: biostudies-literature

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Calibrated bold fMRI with an optimized ASL-BOLD dual-acquisition sequence.

Fernández-Seara María A MA Rodgers Zachary B ZB Englund Erin K EK Wehrli Felix W FW

NeuroImage 20160805

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 CO2 or O2). Here we describe an ASL ...[more]

PMID: 27502047

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Project description:PurposeTo investigate and mitigate the influence of physiological and acquisition-related parameters on myocardial blood flow (MBF) measurements obtained with myocardial Arterial Spin Labeling (myoASL).MethodsA Flow-sensitive Alternating Inversion Recovery (FAIR) myoASL sequence with bSSFP and spoiled GRE (spGRE) readout is investigated for MBF quantification. Bloch-equation simulations and phantom experiments were performed to evaluate how variations in acquisition flip angle (FA), acquisition matrix size (AMS), heart rate (HR) and blood T1$$ {\mathrm{T}}_1 $$ relaxation time ( T1,B$$ {\mathrm{T}}_{1,B} $$ ) affect quantification of myoASL-MBF. In vivo myoASL-images were acquired in nine healthy subjects. A corrected MBF quantification approach was proposed based on subject-specific T1,B$$ {\mathrm{T}}_{1,B} $$ values and, for spGRE imaging, subtracting an additional saturation-prepared baseline from the original baseline signal.ResultsSimulated and phantom experiments showed a strong dependence on AMS and FA ( R2$$ {R}^2 $$ >0.73), which was eliminated in simulations and alleviated in phantom experiments using the proposed saturation-baseline correction in spGRE. Only a very mild HR dependence ( R2$$ {R}^2 $$ >0.59) was observed which was reduced when calculating MBF with individual T1,B$$ {\mathrm{T}}_{1,B} $$ . For corrected spGRE, in vivo mean global spGRE-MBF ranged from 0.54 to 2.59 mL/g/min and was in agreement with previously reported values. Compared to uncorrected spGRE, the intra-subject variability within a measurement (0.60 mL/g/min), between measurements (0.45 mL/g/min), as well as the inter-subject variability (1.29 mL/g/min) were improved by up to 40% and were comparable with conventional bSSFP.ConclusionOur results show that physiological and acquisition-related factors can lead to spurious changes in myoASL-MBF if not accounted for. Using individual T1,B$$ {\mathrm{T}}_{1,B} $$ and a saturation-baseline can reduce these variations in spGRE and improve reproducibility of FAIR-myoASL against acquisition parameters.

Dataset Information

Calibrated bold fMRI with an optimized ASL-BOLD dual-acquisition sequence.

Publications

Calibrated bold fMRI with an optimized ASL-BOLD dual-acquisition sequence.

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