Transcript Mapping Cortical Development Using Diffusion Tensor Imaging Jeff Neil, MD, PhD

Mapping Cortical Development
Using Diffusion Tensor Imaging
Jeff Neil, MD, PhD
Departments of Neurology, Radiology and Pediatrics
MR Imaging
• Detect signal from 1H of H2O, which is present at a
concentration of approximately 100 M.
• In conventional imaging, signal intensity (greyscale) is
related to MR relaxation properties of 1H2O such as T1 or
T2 relaxation times.
• Water in grey matter has different T1 and T2 relaxation
times than water in white matter or CSF.
Water motion in white matter
Perpendicular to axons
Parallel to axons
Hindered Diffusion
(diffusion ellipsoid)
without hindrance
with hindrance
WILSON
Ellipsoid Image
Pierpaoli and Basser, Toward a Quantitative Assessment of
Diffusion Anisotropy, Magn. Reson. Med, 36, 893-906 (1996)
Information available through DTI -- Dav
• Related to the overall size of the ellipsoid.
• Values for Dav change with brain maturation.
• Values of Dav change dynamically after injury
(useful for early detection of injury).
Diffusion MR Imaging of Stoke
Five hours after onset right hemiparesis and aphasia
T2W
DWI
Courtesy of Jonathan Lewin, Case Western Reserve/UH of Cleveland
Information available through DTI -- Aσ
1  ( D)
A 
D
2
av
• Related to the shape of the ellipsoid
• Independent of Dav (normalized)
• Zero for a sphere, positive for other shapes
• Sensitive to myelination and cortical development
Normal Adult Brain
Diffusion Tensor Imaging (A)
(A maps)
Information available through DTI –
Orientation of λ1
• Useful for following white matter tracts
Diffusion Tracking of Geniculo-Calcarine Tracts
Conturo et al. Tracking neuronal fiber pathways in the
living human brain PNAS 96, 10422-10427 (1999).
I. Diffusion Anisotropy in Cortical Grey
Matter – Human Studies
McKinstry et al. Radial organization of developing human
cerebral cortex revealed by non-invasive water diffusion
anisotropy MRI, Cereb Cortex, 12, 1237-1243 (2002).
Background
• Nonzero values for diffusion anisotropy have been
described occurring transiently during the cerebral
cortical development:
• Cat [Baratti et al. Proc ISMRM, 5th Annual
Meeting and Exhibition, Vancouver 504 (1997)]
• Pig [Thornton et al. Magn Reson Imaging 15,
433-440 (1997)].
• We measured cerebral cortical anisotropy values
from premature newborn infants.
Whisker Plot:
26 Weeks GA
Whisker Plot:
35 Weeks GA
Diffusion Anisotropy: Cerebral Cortex
M. Marin-Padilla J Comp Neurol 321, 223 (1992)
Cortical Anisotropy Conclusions
• Cerebral cortex in infants less than 36 weeks
gestational age (GA) has nonzero anisotropy values.
• Cortical A values decrease with increasing GA
(rank sum = -0.94, p < 0.01) and are consistent with
zero after 36 weeks GA.
• Changes in diffusion anisotropy reflect changes in
underlying cortical architecture.
• Diffusion anisotropy measures may have a role in
assessing cortical development and its response to
injury.
II. Diffusion Anisotropy in Cortical Grey
Matter – Preliminary Baboon Data
Experimental Design
• Evaluated immersion-fixed tissue supplied by the
Southwest Foundation in San Antonio (Drs. Jackie
Coalson, Brad Yoder, Don McCurnin).
• Specimens available from 90 days (20 weeks)
through 182 days (40 weeks).
• 450 mm3 spatial resolution.
• 40 q or b values
• Bayesian probability theory for model selection and
parameter estimation (Drs. Chris Kroenke, G. Larry
Bretthorst).
Model
Selection
No Constant
Diffusion + C
No Signal
Constant
Isotropic
Oblate
Prolate
DTI
Model
Selection
Anisotropy Maps
90
128
182
146
0.0
0.2
0.4
0.6
Ellipsoid Map
D
Whisker
Plot
Baboon Study Conclusions
• Anisotropy features of fixed baboon brain are
remarkably similar to those of live premature infants.
• Models for cortical anisotropy tend to be fairly simple
(axisymmetric, prolate, include “constant”).
• Similar information can be obtained from human
infants using fewer b or q values (i.e., with shorter
scan times than for baboon tissue).
• Studies of tissue from injured baboons (and
humans) are under way.
Terrie E. Inder, MD, PhD
Chris Kroenke, PhD
G. Larry Bretthorst, PhD
Robert C. McKinstry, MD, PhD
Amit Mathur, MD
Jeff Miller, MD
I. Alpay Ozcan, DSc
Georgia Schefft, CPNP
Shelly I. Shiran, MD
Joshua S. Shimony, MD, PhD
Avi Z. Snyder, MD, PhD
C. Robert Almli, PhD
NS37357