Comparing VASO and BOLD responses elicited by different hand movement rates at 7T

Poster No:

Th535 

Submission Type:

Abstract Submission 

Authors:

Icaro Oliveira1,2, Serge O. Dumoulin1,2,3, Wietske van der Zwaag4, Jeroen Siero5,1

Institutions:

1Spinoza Centre for Neuroimaging, Amsterdam, Netherlands, 2Experimental and Applied Psychology, VU University, Amsterdam, Netherlands, 3Experimental Psychology, Helmholtz Institute, Utrecht University,, Utrecht,, Netherlands, 4Spinoza center, Amsterdam, Netherlands, 5Radiology, University Medical Centre Utrecht, Utrecht, Netherlands

Introduction:

The motor cortex blood oxygenation level-dependent (BOLD) response corresponds, unlike neural responses, in a non-linear fashion to the movement frequency (Siero et al. 2013). Specifically, the BOLD response saturates at higher movement frequencies. One of the hypotheses for this BOLD response non-linearity is that large draining vessels exhibit response saturation at fast movement rates, i.e. this is a vascular nonlinearity. Cerebral blood volume (CBV) measurements are an alternative fMRI approach to BOLD. The Vascular space occupancy (VASO) contrast is sensitive to arterial CBV changes and promises higher microvascular specificity (Jin and Kim 2008; Kim and Ogawa 2012), thus better spatial localization of neuronal activity, with reduced contamination of draining veins compared to BOLD (Huber et al. 2017). Our hypothesis is that the expected higher microvascular specificity of VASO will result in a reduced vascular nonlinearity effects and thus a more linear response behavior with movement rate compared to BOLD.

Methods:

Four healthy volunteers participated in the study (19-30 years old, 3 male). Imaging was performed on a 7T Philips System using a 32-channel head coil for reception (Nova Medical).
SS-SI VASO images were obtained using a 3D single-shot GRE-EPI sequence with the following parameters: TR/TE=44/17 ms, FA=20°, FOV=190x190x15 mm3, matrix= 127x127 with 10 slices and 1.5mm isotropic voxels. SENSE=2.5, TI1/TI2/ TRVASO=1300/2900/3200 ms and an inversion slab thickness of 260 mm centered on the imaging volume, resulting in an effective 130mm inversion slab below the imaging volume. In an additional subject the inversion slab thickness was varied to inspect inflow (200/240/260/280/300 mm).
The task consisted of closing both hands on a visual cue from a rest position at three different movement intervals: every 2, 1 and 0.5 seconds, or 0.5, 1 and 2Hz. The hand movements were executed for 12 seconds followed by 24 seconds of rest, defined as one trial. In total 12 trials were performed for each movement rate, and the order of the movement rates was randomized across subject.
With SS-SI VASO implementation (Huber et al. 2014), we were able to assess VASO-CBV and BOLD contrast simultaneously. Data processing consisted of a BOLD contamination correction (Huber et al. 2014), necessary at higher field strength as BOLD contrast (extravascular signal) counteracts with the negative VASO signal and smoothing with a FWHM kernel of 2mm3 using SPM12. A GLM analysis was made using FEAT in FSL.
The ROIs were defined as follows: Per subject, the voxels responding significantly (z > 2.3) at all movement rates within a hand-drawn M1/S1 ROI were selected for VASO and BOLD separately. Average percentage signal changes were extracted for each ROI for all movement rates.

Results:

In Figure 1 we can see an example of significant signal changes for all frequency rates. VASO responses were less spatially extensive for all subjects and all movement rates. Inflow was judged minimal for an inversion slab of 260 mm (115 mm below the imaging slab). In Figure 2, the relative amplitude of both functional contrasts is plotted against stimulus frequency, showing a linear dependence of the VASO signal to movement frequency while the BOLD response shows a clear nonlinear dependence.
Supporting Image: fig1.jpg
Supporting Image: fig2.jpg
 

Conclusions:

We successfully implemented SS-SI VASO, and we were able to measure CBV and BOLD changes simultaneously during a hand-movement task. Care should be taken in fine-tuning the inversion slab thickness for VASO, as CBV signals can be contaminated by inflow of non-inverted blood.
As expected, we observed a strong nonlinear dependency of the BOLD response with movement rate. In contrast, the VASO response behavior showed a clear linear dependence with movement rate, suggesting tighter neural coupling. These findings highlight the microvascular specificity (arterial side) of VASO fMRI.

Imaging Methods:

BOLD fMRI 2
Non-BOLD fMRI 1

Keywords:

Blood
Cerebral Blood Flow
fMRI CONTRAST MECHANISMS
FUNCTIONAL MRI
HIGH FIELD MR
Motor
MRI PHYSICS

1|2Indicates the priority used for review

My abstract is being submitted as a Software Demonstration.

No

Please indicate below if your study was a "resting state" or "task-activation” study.

Task-activation

Healthy subjects only or patients (note that patient studies may also involve healthy subjects):

Healthy subjects

Was any human subjects research approved by the relevant Institutional Review Board or ethics panel? NOTE: Any human subjects studies without IRB approval will be automatically rejected.

Yes

Was any animal research approved by the relevant IACUC or other animal research panel? NOTE: Any animal studies without IACUC approval will be automatically rejected.

Not applicable

Please indicate which methods were used in your research:

Functional MRI

For human MRI, what field strength scanner do you use?

7T

Which processing packages did you use for your study?

SPM
FSL

Provide references using author date format

Huber, Laurentius et al. 2014. “Slab-Selective, BOLD-Corrected VASO at 7 Tesla Provides Measures of Cerebral Blood Volume Reactivity with High Signal-to-Noise Ratio.” Magnetic Resonance in Medicine 72(1): 137–48.
Huber, Laurentius et al. 2017. “High-Resolution CBV-FMRI Allows Mapping of Laminar Activity and Connectivity of Cortical Input and Output in Human M1.” Neuron 96(6): 1–11. http://dx.doi.org/10.1016/j.neuron.2017.11.005.
Jin, Tao, and Seong Gi Kim. 2008. “Improved Cortical-Layer Specificity of Vascular Space Occupancy FMRI with Slab Inversion Relative to Spin-Echo BOLD at 9.4 T.” NeuroImage 40(1): 59–67.
Kim, Seong-Gi, and Seiji Ogawa. 2012. “Biophysical and Physiological Origins of Blood Oxygenation Level-Dependent FMRI Signals.” Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism 32(7): 1188–1206. http://www.ncbi.nlm.nih.gov/pubmed/22395207 (December 5, 2018).
Siero, Jeroen C.W. et al. 2013. “BOLD Consistently Matches Electrophysiology in Human Sensorimotor Cortex at Increasing Movement Rates: A Combined 7T FMRI and ECoG Study on Neurovascular Coupling.” Journal of Cerebral Blood Flow and Metabolism 33(9): 1448–56. https://doi.org/10.1038/jcbfm.2013.97.