The orientation-dependence of stria of Gennari ex vivo in high-resolution MRI phase data

Poster No:

1845 

Submission Type:

Abstract Submission 

Authors:

Anna Blazejewska1, Lucia Navarro De Lara1, Berkin Bilgic1, Divya Varadarajan1, Andre van der Kouwe1, Jean Augustinack1, Bruce Fischl1, Jonathan Polimeni1,2

Institutions:

1Athinoula A. Martinos Center for Biomedical Imaging, MGH/Harvard Medical School, Charlestown, MA, 2Division of Health Sciences and Technology, MIT, Cambridge, MA

First Author:

Anna Blazejewska  
Athinoula A. Martinos Center for Biomedical Imaging, MGH/Harvard Medical School
Charlestown, MA

Co-Author(s):

Lucia Navarro De Lara  
Athinoula A. Martinos Center for Biomedical Imaging, MGH/Harvard Medical School
Charlestown, MA
Berkin Bilgic  
Athinoula A. Martinos Center for Biomedical Imaging, MGH/Harvard Medical School
Charlestown, MA
Divya Varadarajan, PhD  
Athinoula A. Martinos Center for Biomedical Imaging, MGH/Harvard Medical School
Charlestown, MA
Andre van der Kouwe  
Athinoula A. Martinos Center for Biomedical Imaging, MGH/Harvard Medical School
Charlestown, MA
Jean Augustinack, PhD  
Athinoula A. Martinos Center for Biomedical Imaging, MGH/Harvard Medical School
Charlestown, MA
Bruce Fischl  
Athinoula A. Martinos Center for Biomedical Imaging, MGH/Harvard Medical School
Charlestown, MA
Jonathan Polimeni, Ph.D.  
Athinoula A. Martinos Center for Biomedical Imaging, MGH/Harvard Medical School|Division of Health Sciences and Technology, MIT
Charlestown, MA|Cambridge, MA

Introduction:

The stria of Gennari is a band of highly myelinated axons located in Layer IVb of human primary visual cortex (V1) which anatomically appears as an approximately 0.3 mm thick stripe on average[1]. It has been shown that due to its myelination stria can be directly visualized using high-resolution MRI via decreased T1[2] and magnetization-transfer contrast[3], [4]. The stria is also known to appear hypointense in gradient-echo T2*-weighted (T2*-w) magnitude and phase images, which has been attributed to high iron concentration within Layer IV manifesting as a magnetic susceptibility offset[5]–[7]. Contributions of both iron and myelin derived from histological staining and iron quantification have been shown to be collocated with the putative stria of Gennari seen in high-resolution ex vivo MRI[8]. Here, we investigate the effect of orientation of the stria in relation to the direction of B0 magnetic field on its appearance in the phase component of the T2*-w MRI, which could aid the understanding of microstructural tissue composition and the dominant fiber orientations comprising the stria across regions of V1.

Methods:

An ex vivo brain specimen (49 y.o. M) fixed in periodate-lysine-paraformaldehyde (PLP) was sectioned to obtain a tissue block (≈4×4×6 cm) containing V1 identified in the gross anatomy by the calcarine sulcus (F1a). The sample was placed in a sealed container, immersed in PLP and imaged at 7T using a whole-body scanner (MAGNETOM, Siemens, Germany) equipped with a custom build 5-turn solenoid coil (F1c). The data were acquired with 3D multi-echo T2*-w sequence at isotropic resolution of 150 μm with six echo times (TEs, F1e). Five scans were acquired with different orientations of the sample with respect to the direction of the B0 magnetic field (F1b&d2d). In addition, T1-w MEMPRAGE data[9] were acquired at orientation 0° with TI=900 ms optimized to null the signal from sample surroundings.
Phase data were spatially unwrapped, and for each orientation mean images of phase and magnitude were calculated using four middle TEs which exhibited the strongest contrast between the stria and the surrounding intracortical GM in the magnitude data. The images were aligned to the orientation 0° using robust registration[10] with 12 DOF and nearest neighbor interpolation. The phase images were spatially high-pass filtered to remove background phase and spatially 3D gaussian-smoothed (FWHM=0.2 mm). MEMPRAGE images were aligned with the T2*-w magnitude data for each orientation and thresholded to create binary tissue masks. Regions of interest (ROIs) were manually outlined in the stria of Gennari identified on the magnitude images, and phase values averaged within these regions were plotted as a function of sample orientation relative to the B0 axis.
Supporting Image: F0001.png
   ·F1
 

Results:

We found that the appearance of stria of Gennari in the phase data was highly dependent on the orientation of the sample with respect to the B0 magnetic field (F2a&b). In the coronal and sagittal planes, which were parallel to the B0 direction (F1d&2a), the relative phase values of different regions of the stria changed from negative to positive (or from positive to negative) with varying of the sample orientation (F2b&c). In contrast, in the axial plane, which was perpendicular to the B0 direction (F1d&2a), the relative phase values within the ROIs remained within the same range across the sample orientations (F2b&c).
Supporting Image: F002.png
   ·F2
 

Conclusions:

Here we demonstrate a strong orientation-dependent appearance of stria of Gennari observed in the phase data of a high-resolution gradient-echo acquisition ex vivo which could be potentially used to gain insights into tissue composition and to derive dominating directions of the fibers located in the stria. In addition, while phase-valued images benefit from a strong contrast of the stria and the surrounding intracortical tissue, the orientation dependence may affect the detection reliability of the stria throughout V1 and confound the V1 border identification.

Neuroanatomy, Physiology, Metabolism and Neurotransmission:

Cortical Anatomy and Brain Mapping 1
Cortical Cyto- and Myeloarchitecture 2

Novel Imaging Acquisition Methods:

Anatomical MRI

Keywords:

Cortex
Cortical Layers
HIGH FIELD MR
MRI
Myelin
Other - ex vivo

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.

Other

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:

Structural MRI

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

7T

Which processing packages did you use for your study?

FSL
Free Surfer

Provide references using author date format

[1] C. von Economo and G. Koskinas, Atlas of Cytoarchitectonics of the Adult Human Cerebral Cortex. 2008.
[2] S. Eickhoff et al., “High-resolution MRI reflects myeloarchitecture and cytoarchitecture of human cerebral cortex,” Hum. Brain Mapp., vol. 24, no. 3, pp. 206–215, 2005.
[3] R. Turner, A. M. Oros-Peusquens, S. Romanzetti, K. Zilles, and N. J. Shah, “Optimised in vivo visualisation of cortical structures in the human brain at 3 T using IR-TSE,” Magn. Reson. Imaging, vol. 26, no. 7, pp. 935–942, 2008.
[4] O. Mougin, M. Clemence, A. Peters, A. Pitiot, and P. Gowland, “High-resolution imaging of magnetisation transfer and nuclear Overhauser effect in the human visual cortex at 7T.,” NMR Biomed., Jun. 2013.
[5] A. Deistung, A. Schäfer, F. Schweser, U. Biedermann, R. Turner, and J. R. Reichenbach, “Toward in vivo histology: A comparison of quantitative susceptibility mapping (QSM) with magnitude-, phase-, and R2*-imaging at ultra-high magnetic field strength,” Neuroimage, vol. 65, pp. 299–314, 2013.
[6] J. H. Duyn, P. Van Gelderen, T. Li, J. A. De Zwart, A. P. Koretsky, and M. Fukunaga, “High-field MRI of brain cortical substructure based on signal phase,” 2007.
[7] K. Shmueli, J. a de Zwart, P. van Gelderen, T.-Q. Li, S. J. Dodd, and J. H. Duyn, “Magnetic susceptibility mapping of brain tissue in vivo using MRI phase data.,” Magn. Reson. Med., vol. 62, no. 6, pp. 1510–22, Dec. 2009.
[8] M. Fukunaga et al., “Layer-specific variation of iron content in cerebral cortex as a source of MRI contrast.,” PNAS, vol. 107, no. 8, pp. 3834–9, Feb. 2010.
[9] A. J. W. van der Kouwe, T. Benner, D. H. Salat, and B. Fischl, “Brain morphometry with multiecho MPRAGE,” Neuroimage, vol. 40, no. 2, pp. 559–569, Apr. 2008.
[10] M. Reuter, H. D. Rosas, and B. Fischl, “Highly accurate inverse consistent registration: A robust approach,” Neuroimage, vol. 53, no. 4, pp. 1181–1196, 2010.

Acknowledgements
This work was supported in part by the BRAIN Initiative (NIH NIMH K99MH120054 and R01-MH111419, and NIBIB U01-EB025162) and NIH NIBIB grants (P41-EB015896 and R01-EB019437), and by the MGH/HST Athinoula A. Martinos Center for Biomedical Imaging; and was made possible by the resources provided by NIH Shared Instrumentation Grants S10-RR023043 and S10-RR019371.