Simultaneous mapping of T2* and major neurotransmitters using MRSI at 3T

Poster No:

2056 

Submission Type:

Abstract Submission 

Authors:

Fatimah Almomen1, Pingyu Xia1, Xiaopeng Zhou1, Mark Chiew2, Adam Steel3, Albert Thomas4, Ulrike Dydak1, uzay Emir1

Institutions:

1Purdue University, West Lafayette, IN, 2Oxford University, Oxford, OXford, 3Dartmouth College, Hanover, NH, 4David Geffen School of Medicine at UCLA, Los Angeles, CA

First Author:

Fatimah Almomen  
Purdue University
West Lafayette, IN

Co-Author(s):

Pingyu Xia  
Purdue University
West Lafayette, IN
Xiaopeng Zhou  
Purdue University
West Lafayette, IN
Mark Chiew  
Oxford University
Oxford, OXford
Adam Steel  
Dartmouth College
Hanover, NH
Albert Thomas  
David Geffen School of Medicine at UCLA
Los Angeles, CA
Ulrike Dydak  
Purdue University
West Lafayette, IN
uzay Emir  
Purdue University
West Lafayette, IN

Introduction:

Gamma-aminobutyric acid (GABA) and glutamate (Glu) are the brain's primary inhibitory (I) and excitatory (I) neurotransmitters. They are both strongly implicated in functional changes in neural circuitry and to be associated with learning and plasticity 1. The E-I balance/imbalance has been examined non-invasively by using proton (1H) magnetic resonance spectroscopy (MRS) to measure the glutamatergic-GABAergic system 2. MRS imaging (MRSI) methods are superior to single-voxel by recording multiple spectra from different regions simultaneously 3. In this study, we propose using a MEGA semi-LASER sequence with non-water suppressed metabolite-cycling as 2D MRSI data acquisition method at 3T for high-resolution GABA, Glutamate and T2*detection throughout a whole axial slice. Simultaneous measurement T2* with neurotransmitter maps will provide useful information on functional hemodynamic changes due physiological interventions.

Methods:

All scans were acquired using a Siemens Prisma 3-Tesla (Siemens, Erlangen, Germany) whole-body MRI scanner and a 20-channel head array receive coil. B0 shimming was achieved using GRESHIM . The non-water-suppressed metabolite-cycling MRSI acquisition with the semi-LASER localization (TR = 1 s, TE = 68 ms), was used to excite whole brain slice with a 125 mm x 105 mm x 20 mm region centrally within the field of view (FOV= 240 mm x 240 mm) 4. The Gaussian editing pulses of 65 Hz width were placed on the H3' protons at 1.9 ppm in the "ON" acquisition, and at 9.0 ppm in the "OFF" acquisition. To cover the 32x32 grid in the FOV, the density weighted concentric ring trajectory (DW-CRT) with a 1.125 mL (7.5 mm x 7.5 mm x 20 mm) was acquired. The number of averages for the phantom and invivo acquisitions was 2, corresponding to a total acquisition duration of 8.5 minutes. The feasibility of the whole brain slice with the proposed methods was tested on three healthy volunteers (2 males; mean age of 28 year old) after giving informed consent under an institutionally approved technical development protocol. All reconstructions were implemented in MATLAB using the non-uniform FFT (NUFFT) toolbox 5. Lipid contamination was removed during post‐processing using a lipid‐basis penalty algorithm 6. Metabolites were quantified using LCModel 7. The monoexponential model with an the adaptive mask was fit to the water spectrum at each voxel using log-linear regression in order to estimate T2* map using tedana software 8.

Results:

Figure 1 shows the GABA+, Glutamate+Glutamine and T2* maps together with corresponding downsampled segmented gray matter and the edited in vivo MR spectra. The linear regression result of GABA, Glu and T2*maps versus the gray matter fraction is provided in Figure 2. Average T2* values measured for gray matter and white matter were 76 and 64 msec, respectively.
Supporting Image: hbm1.png
   ·Figure 1 Gray matter tissue composition, T2* and metabolic maps and an illustrative spectra
Supporting Image: hbm2.png
   ·Figure 2 Linear regression plot T2*, of GABA+ and Glutamate+glutamine versus gray matter tissue composition.
 

Conclusions:

We have developed and demonstrated a sequence that generates simultaneously GABA+, Glutamate+Glutamine and T2* maps at 3 Tesla, within a clinically feasible acquisition time of 8.5 min. Metabolic maps showed distinct anatomical contrast showed a clear elevation of GABA Glutamate+Glutamine and T2* levels in GM and was in the range of previous of previously published reports9. Experiments demonstrate the advantage of non-water suppressed MEGA semi-LASER MRSI sequence with DW-CRT in terms of its improved resolution and reduced contamination of spectra from neighboring voxels. In addition, simultaneous measurement T2* maps will provide useful information on functional hemodynamic changes due physiological interventions.

Neuroanatomy, Physiology, Metabolism and Neurotransmission:

Cortical Anatomy and Brain Mapping 2

Novel Imaging Acquisition Methods:

MR Spectroscopy 1

Keywords:

FUNCTIONAL MRI
Magnetic Resonance Spectroscopy (MRS)
MR SPECTROSCOPY
MRI
Neurotransmitter

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.

Resting state

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

Healthy subjects

Are you Internal Review Board (IRB) certified? Please note: Failure to have IRB, if applicable will lead to automatic rejection of abstract.

Yes

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?

3.0T

Which processing packages did you use for your study?

AFNI
FSL

Provide references using author date format

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8. DuPre,Elizabeth, GonzalezCastillo, Javier, Handwerker, Daniel, Markello, Ross, Salo, Taylor, Whitaker, Kristie. Tedana: Robust and extensible software for multi-echo denoising. Rome,Italy; 2019 [cited 2019 Dec 11]. p. 4293. Available from: https://ww5.aievolution.com/hbm1901/index.cfm?do=abs.viewAbs&abs=4013
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