Functional
and Anatomical Comparison of Lateral Geniculate Nucleus
in Human Brain using High-Resolution MRI
Wei Chen, Xiao-Hong Zhu, Haiying Liu, Toshinori Kato, Kamil Ugurbil
Department of Radiology, University of Minnesota Medical School, Minneapolis, Minnesota
INTRODUCTION
Subcortical nuclei in the
thalamus are parts of neural network and play an very
important role in many human brain functions. They
provide challenging targets for functional mapping due
to their small sizes and deep locations. Recently, we
had demonstrated the feasibility of using fMRI at 4T
for detecting the activation in the small lateral
geniculate nuclei (LGN) during visual perception and
visual imagery in single experiments(l-3). In these
studies, the spatial assignment of LGN was judged by
adjacent brain anatomical structures in three
orientations.
More precise assignment and
identification of nucleus activation can be achieved by
comparing the functional activation maps with the
nucleus anatomy. However, the small nucleus size
and less relaxation time differentiation between nuclei
and surrounding tissues require high-resolution
anatomy imaging with better image contrasts (4). In
this study, we examine the feasibility for detecting
LGN anatomy using high-resolution anatomical image
and compare the spatial correlation of the LGN
locations detected by anatomical image and highresolution fMRI.
The fMRI
MATERIALS
AND METHODS
studies were nerformed on a 4 Tesla whole body
system using a quadrature head birdcage coil. The
high-resolution multislice EPI technique with four
segmentations, variable flip angles, center-out k-space
sampling, and a navigator echo correction (5) was used
for functional mapping of LGN activation in axial or
coronal planes (128 x 128 matrix size, 20 x 20 cm*
FOV, 3-5 mm slice thickness, TE = 25 ms). The
visual stimulus was composed of two identical
checkerboards arranged side-by-side (16 Hz reversal
frequency). It was used to provide full or hemifield
visual stimulation. The fMRI protocol consists of four
control (darkness) and four task periods in an
interleaved way. Twenty image sets was acquired in
each of the eight consecutive periods (TR = 2 s, five
minutes for each experiment). The fMR1 maps were
generated by comparing images averaged between
conditions on a voxel-by-voxel basis using the period
High-resolution T,cross correlation method.
weighted 3D MDEFT image (6) (128 x 128 x 64
matrix size, 20 x 20 x 18 cm3 FOV, TR/TE = 9 ms/4
m - 6 min acquisition) was used to acquire
anatomical image. This technique provides a superior
image contrasts among cortical and subcortical grey
matters and white matters at high magnetic fields (6).
RESULTS AND DISCUSSION
Figure 1 illustrates the comparison between the
anatomical MDEFT image and the LGN fMRI map
during the full-field visual stimulation. The LGN
anatomy structures are clearly shown in Fig. la (dark
intensity areas) and are outlined in Fig. lb. The LGN .
locations and sizes detected by anatomical image are
consistent with the LGN activation mapped by fMRI
(Fig. lc). These results reveal the advantagesof the
MRI technique for providing both high-resolution
anatomical and fMRI images.
The averageactivation pixel number of LGN in the
coronal plane was 8.6 f 4.5 (14 measurements). This
gives, approximately, the 2D LGN activation size of
5.1 x 5.1 mm2 (considering Gaussian filter),
respectively. The size is consistent with the anatomical
study showing approximately 5 x 6 mm2 sizes of LGN
in the coronal orientation in the human brain (4).
AnatomicalimagesshowingtheLGN anatomyand
(c) fh&l mapshowingtheLGN activation(darkpixels)obtained
at 4T (coronalplanes).Theoutlinesin (b) depictLGN.
Fig. 1 (a, b)
Recently, we have examined another image
sequenceof fast spin echo based technique (TRfTE/TI
= 7000/14/l 80) with a pre-imaging inversion pulse (7)
for obtaining more high spatial resolution anatomy
within a comparatively short scan time. The initial
experiments were conducted at 1.5T. The preliminary
results reveal the capability of the imaging to identify
the LGN boundary. This makes it possible to estimate
the LGN size of -4.5 mm in the coronal plane which is
in agreementwith the results from this fMRI study and
literature (4).
CONCLUSION
Our results demonstrate the
capability of high-resolution anatomical image for
identifying small nuclei in the thalamus. This is
important for fMRI to precisely define nucleus
activation and differentiate adjacent nucleus activation.
It provides a methodology using fMRI for functional
mapping of neural networks encompassingboth cortical
and sub-cortical grey matters in the human brain.
This research was supported
NS38070 and P41 RR08079.
by NIH
gran,ts
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