Prog Med Phys.  2019 Mar;30(1):22-31. 10.14316/pmp.2019.30.1.22.

b0 Dependent Neuronal Activation in the Diffusion-Based Functional MRI

• Kim HG
• Jahng GH

• KMID: 2442418
• DOI: http://doi.org/10.14316/pmp.2019.30.1.22

Abstract

PURPOSE
To develop a new diffusion-based functional MRI (fMRI) sequence to generate apparent diffusion coefficient (ADC) maps in single excitation and evaluate the contribution of b0 signal on neuronal changes.
MATERIALS AND METHODS
A diffusion-based fMRI sequence was d esigned with single measurement that can acquire images of three directions at a time, obtaining b = 0 s/mm2 during the first baseline condition (b0_b), followed by 107 diffusion-weighted imaging (DWI) with b = 600 s/mm2 during the b aseline and visual stimulation conditions, and another b = 0 s/mm2 during the last activation condition (b0_a). ADC was mapped in three different ways: 1) using b0_b (ADC_b) for all time points, 2) using b0_a (ADC_a) for all time points, and 3) using b0_b and b0_a (ADC_ba) for baseline and stimulation scans, respectively. The fMRI studies were conducted on the brains of 16 young healthy volunteers using visual stimulations in a 3T MRI system. In addition, the blood oxygen level dependent (BOLD) fMRI was also acquired to compare it with diffusion-based fMRI. A sample t-test was used to investigate the voxel-wise average between the subjects.
RESULTS
The BOLD data consisted of only activated voxels. However, ADC_ba data was observed in both deactivated and activated voxels. There were no statistically significant activated or deactivated voxels for DWI, ADC_b, and ADC_a.
CONCLUSIONS
With the new sequence, neuronal activations can be mapped with visual stimulation as compared to the baseline condition in several areas in the brain. We showed that ADC should be mapped using both DWI and b0 images acquired with the same conditions.

Keyword

Brain function; Functional MRI; Diffusion; ADC; BOLD

MeSH Terms

Brain
Diffusion
Healthy Volunteers
Magnetic Resonance Imaging*
Neurons*
Oxygen
Photic Stimulation
Oxygen

Figure

• 

  Fig. 1 Diagrams of the diffusion-based functional MRI sequence (a) and the gradient for diffusion-weighting (b). Diffusion gradients were applied on the three axes to map isotropic apparent diffusion coefficient in a single acquisition. (a) RF, radio frequency; Gx, readout direction; Gy, phase-encoding direction; Gz, slice-selection direction; TE, echo time; TR, repetition time; and Echo, echo signal. (b) g, gradient strength; δ, duration of the diffusion gradient; ε, length of slope (ramp time); Δ, diffusion time.

• 

  Fig. 2 The scan orders (a) and the stimulation paradigm (b) for the diffusion-based functional MRI acquisitions. The same stimulation paradigm was applied on the BOLD fMRI scans. b0_b, the first baseline scan; b0_a, the last activation scan; DWI, diffusion-weighted imaging scans.

• 

  Fig. 3 Results of BOLD (a) and ADC_ba (b) for activated and deactivated brain regions for visual stimulation over 15 subjects. The results for activation and deactivation are observed with P<0.001 for correcting multiple comparisons using a false discovery rate (FDR), respectively. In the blood oxygen level-dependent (BOLD) data, increased (red) neuronal activations were found during the visual stimulation, and no deactivation areas were observed. In the ADC_ba data, increased (red) and decreased (blue) neuronal activations were found during the visual stimulation. ADC_ba was apparent diffusion coefficient (ADC) mapped with using both b0_b and b0_a for the baseline scans and activation scans, respectively. The color-coded maps are overlaid on the standard axial T1 template.

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