CHAPTER 11: High-Resolution and Microscopic Imaging at High Field
Figure 1. Single frame from an in-vivo mouse cardiac CINE study. Short axis frames from
a fully refocused FLASH scan, FOV = 3 cm, 200 x 200 image matrix, TE/flip angle = 2.7
ms/30º, 4 averages, 16 frames per RR interval. The anesthetized mouse heart was beating
at a rate of 450–600 bpm. Image courtesy of David Sosnovik, MD and George Dai, PhD of
the Program in Cardiovascular Magnetic Resonance, MGH, A.A. Martinos Center for
Biomedical Imaging.
Figure 2. 7T human image (right) and 3T image (left) obtained with identical pulse
sequence parameters, console, and gradient coil. Both obtained with volume head coil.
The intensity of the 7T image has been intensity normalized to flatten the low spatial frequency dielectric lensing effect. The SNR of the 7T image. exceeds the 3T acquisition by as
much as a factor of 3 in the deep tissue, where dielectric effects aid the sensitivity to somewhat below a factor of 2 in the cortical areas.
CHAPTER 11: High-Resolution and Microscopic Imaging at High Field
Figure 3. 8T gradient echo human image courtesy of P. Robitaille and colleagues of the
Ohio State University (20 cm FOV, 2000 x 2000 gradient echo encoding).
Figure 4. Photo of a 3T 8-channel receive-only array coil with its developer, Graham
Wiggins, PhD of the A.A. Martinos Center at MGH. The coil, comprised of 8-cm diameter
elements, provides wraparound coverage of a large area of cortex. High-resolution T2 weighted TSE image, 15 echoes, TR/TE = 1680/97 ms, FOV = 170 x 200 mm, 336 x 512
matrix (400 μm resolution), 3-mm slice, acq. time = 7:25 min. Image intensity normalized
for surface coil drop-off. The SNR gain of this coil (compared to commercial birdcage
headcoil) was fourfold in the near cortex and a factor of 1.3-fold in the center of the head.
CHAPTER 11: High-Resolution and Microscopic Imaging at High Field
Figure 5. Coronal Turbo Spin Echo image of the human occipital pole obtained at 7 T using
an 8-channel wraparound coil similar to that in Figure 4. The increased myelination band
in layer IV (line of Gennari) can be visualized with a conventional clinical scan time (7
minutes). In plane resolution of 330 μm and 2-mm thick slices (220 nl voxel volumes).
Figure 6. 32-channel array coil developed in collaboration with Graham Wiggins, PhD of
the MGH, A.A. Martinos Center. Image resolution is 0.5 x 0.5 x 1 mm (250 nl voxel volumes).
CHAPTER 11: High-Resolution and Microscopic Imaging at High Field
Figure 7. 90-channel array coil shown with its developer, Graham Wiggins, PhD of the
MGH, A.A. Martinos Center. The extremely small elements can provide greatly increased
sensitivity near the coil if they can maintain body-load dominance. The large number of
noninteracting detectors can boost signal in the center of the head to exceed that of conventional detectors.
Figure 8. Sagittal section of the ex-vivo human occipital lobe from a 3D isotropic proton
density-weighted FLASH scan acquired at 7 T with 120 μm isotropic resolution (1.7-nl
voxel volume); acquisition time = 4 hours. Surface coil acquisition has been intensity normalized. The line of Gennari defining the Brodmann area 17 can be seen as an increase in
myelin content (and thus a darker signal area) in the proton density-weighted scan.
CHAPTER 11: High-Resolution and Microscopic Imaging at High Field
Figure 9. Reformated section of the ex-vivo human parietal lobe from a 3D isotropic proton density and T2*-weighted FLASH scan acquired at 7 T with 150-μm isotropic resolution (nominal voxel volume = 3.4 nl). TR/TE/flip angle = 55 ms/20 ms/10º, acquisition
time = 1 hour. Myelin structures suggestive of the internal and external lines of Baillarger
can be seen, especially in the thickened crowns of the gyrus.
Figure 10. 7T macaque brain images. T1 map at 200 x 200 x 1000 μm resolution (nominal
voxel volume = 40 nl) computed from 8 inversion times in a 2D Turbo Spin Echo image.
Grey, white, and V1 layer 4b T1 values were found to be 1360, 920, and 1180 ms, respectively.
CHAPTER 11: High-Resolution and Microscopic Imaging at High Field
Figure 11. Sagittal detail from 7 Tesla 3D T1-weighted MPRAGE scan of in-vivo macaque
brain. Resolution = 250 x 250 x 750 μm (voxel volume = 47 nl). Intensity profile from the
line shown on the image showing increased signal intensity at the location expected for
layers I and IVb. All images were acquired with 5-cm diameter receive-only and10-cm
diameter transmit-only surface coils.
Figure 12. Sagittal detail from 7 Tesla 3D T1-weighted MPRAGE scan of in-vivo macaque
brain showing reproducibility of the laminar features across slices and hemispheres.
Resolution = 250 x 250 x 750 μm (voxel volume = 47 nl). All images were acquired with 5cm diameter receive-only and 10-cm diameter transmit-only surface coils.
CHAPTER 11: High-Resolution and Microscopic Imaging at High Field
Figure 13. Original in-vivo data (left) and Gibbs simulation of macaque visual cortex. The
Gibbs simulation consists of a high-resolution three-component model based on the original image, which was then truncated in the k-space domain to the resolution of the original image.
Figure 14. Transmantle dysplasia — axial T2 FSE (left) and axial MPRAGE, a thin section
volumetric T1-weighted sequence (right) obtained with a 3T PA MRI. A cone-shaped
region of increased T2 signal begins at the ventricular margin and extends to the depth of
a sulcus (arrow), seen as a more subtle region of decreased T1 signal (arrow, right). Image
courtesy of S. Knake and P.E. Grant, MGH Martinos Center.
CHAPTER 11: High-Resolution and Microscopic Imaging at High Field
Figure 15. Effects of GD on (left to right) T1, PD, T2*, and optimal CNR for 0, 1, 5, and 10mM concentrations.
Figure 16. Image of the ex-vivo MTL (left) acquired at 7 T with 100 μm isotropic voxels (TR
= 20, TE = 5, flip = variable). Nominal voxel volume = 1 nl. Right: oblique slice through
layer II of EC showing the layer II islands as brighter regions. Layers in the CA fields of
the hippocampus and the dentate gyrus are clearly visible. Image in collaboration with
Jean Augustinack, PhD and Megan Blackwell.
Figure 17. Example of a bock face image (left), a Nissl stain (center), and a high-resolution
MRI (right, 7 T), same as Figure 16.