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B3-11
ADVANCED DIFFUSION MRI METHODS TO QUANTITA-
TIVELY DISTINGUISH BETWEEN COMPLEX WHITE
MATTER AND TRAUMATIC AXONAL INJURY
Mihika Gangolli
1
, Joong Hee Kim
1
, Laurena Holleran
1
, Victor
Alvarez
2
, Thor Stein
2
, Ann McKee
2
, David L. Brody
1
1
Washington University in St. Louis, School of Medicine, St. Louis, USA
2
Boston University, CTE Center, Boston, USA
Chronic traumatic encephalopathy (CTE) is a progressive neurode-
generative condition that occurs following repetitive mild traumatic
brain injury. Its distinct neuropathological features, including phos-
phorylated tau tangles and axonal degeneration, can be detected post-
mortem via staining, but remain invisible to current imaging methods.
Diffusion weighted imaging has been proposed as a noninvasive de-
tection method due to its high sensitivity to microstructural changes in
brain tissue integrity. This approach is complicated by the assumption
that diffusion in a voxel can be modeled using a single Gaussian dis-
tribution, leading to ambiguous results when attempting to distinguish
axon degeneration from uninjured regions with complex fiber archi-
tecture. We demonstrate through alternative diffusion imaging methods
and quantitative histology that diffusion imaging can distinguish be-
tween complex fiber architectures and injured axon regions.
Human ex vivo cortical tissue was scanned using an 11.7T Varian
MRI scanner, 202 diffusion weighted gradient directions, and a voxel
size of 250x250x500
l
m. Diffusion based directionality was calcu-
lated using both diffusion tensor and generalized q-space (GQI)
models. The tissue was then serially sectioned into 50
l
m slices and
stained for myelinated axons using Black Gold II. Two dimensional
Fourier transforms of Black Gold II stained images were used to
quantify histological fiber directionality of each 250x250x500
l
m
region. Registration of the histological data to the diffusion data was
performed by placing landmarks in both data sets and applying a
similarity transform to the histological image.
Using an ROI based analysis, we found that regions with complex
distributions of fiber orientations also had reduced fractional anisot-
ropy in diffusion tensor imaging, while the generalized fractional
anisotropy from GQI was not reduced. These findings demonstrate
that advanced diffusion weighted imaging can account for complex
white matter structures and is likely provide a more specific means of
quantitatively assessing axon directionality and injury.
Keywords: Ex vivo study, Diffusion weighted imaging, Fiber di-
rection, Histological correlation
B3-12
BLAST INDUCED SPATIAL AND TEMPORAL ALTERA-
TIONS IN GLIAL EXPRESSION AND AXONAL INJURY IN
THE RAT SPINAL CORD
Liying Zhang
, Srinivasu Kallakuri, Heena Purkait, Satya Dalavayi,
Karthika Andrew, John Cavanaugh
Wayne State University, Biomedical Engineering, Detroit, USA
Blast induced neurotrauma is a signature wound of veterans returning from
military operations. With much of the research focus being directed at
understanding blast wave induced changes in the brain knowledge related
to blast effect in the spinal cord remains unresolved. Knowledge related to
injury changes in the spinal cord following blast overpressure may help
understand altered sensory problems often reported by veterans. In fact, a
high prevalence of chronic pain, particularly in the back (58%) and head
(55%) in some veterans was also reported. Whether blast overpressure
induces injury changes in the spinal cord and if these changes contribute to
acute or chronic sensory changes is a fundamental question that is yet to be
addressed. We postulate that blast overpressure induces changes in the
spinal cord in the form of glial activation and axonal injury. Anesthetized
male SD rats were subjected to a single insult of blast overpressure (22 psi)
induced by a custom-built shock tube. Rats were divided into groups based
on their survival period: 6 hours, 24 hours, 3 days and 7 days. The spinal
cord segments (cervical, thoracic and lumbar) were cut horizontally into
40
l
m thick serial sections. Astrocytic and microglial activation was re-
vealed by Glial fibrillary acidic protein (GFAP) and ionized calcium-
binding adapter molecule 1 (Iba1) immunohistochemistry. Axonal injury
was revealed by neurofilament light chain immunohistochemistry. The
extent of astrocytic and microglial activation was quantified by counting
their number from representative images taken from cervical, thoracic and
lumbar spinal cord sections. Elevated astrocyte and microglial counts were
observed in blast spinal cord compared to sham. Temporally, significantly
high astrocytes were observed in different regions of the spinal cord.
Axonal injury changes were observed in all spinal cord segments at var-
ious time periods after blast. Taken together these findings support that
blast induced injury changes extend into spinal cord and may contribute to
altered neuronal function.
Keywords: Shock tube, Blast induced spinal cord injury, Rats,
Astrocytic and microglial activation
B3-13
OPEN FIELD PRIMARY BLAST EXPOSURE INDUCES NEU-
RONAL AND GLIAL ALTERATIONS IN FRONTAL CORTEX
Liying Zhang
, Srinivasu Kallakuri, Alok Desai, Janine Mathei, Elizabeth
Dawe, Ke Feng, Chaoyang Chen, John Cavanaugh, Albert King
Wayne State University, Biomedical Engineering, Detroit, USA
The wars in Iraq and Afghanistan have highlighted the emergence of
Blast Induced Neurotrauma (BINT) and the associated mild traumatic
brain injury as the signature wound in returning service members.
Several animal studies showed axonal injuries, myelin and cytoskeletal
breakdown, cell death and glial activation as part of efforts in under-
standing the pathological changes in brain after blast. However, detailed
studies aimed at characterizing cellular injury changes in a gyr-
encephalic primary blast exposure model are still limited which forms
the purpose of this study. Anesthetized male Yucatan swine (50–60 kg)
were exposed either to medium (224–332 kPa; n
=
7) or high over-
pressure (350–403 kPa; n
=
5) open-field blast. Sham animals (n
=
5)
were not subjected to blast. After a 3-day survival period, the frontal
cortex of the perfused brain was cut into 5mm blocks which were then
cut into 40
l
m thick serial sections. Sections were then processed to
assess axonal injury (
b
-APP-beta amyloid precursor protein), glial
proliferation (glial fibrillary acidic protein; ionized calcium-binding
adapter molecule 1) and cellular injury (cleaved caspase 3 and H&E
staining). Prominent diffuse axonal injury in the form of
b
-APP im-
munoreactive swollen axons and retraction balls was observed in the
high overpressure group. Also observed were prominent white and grey
matter
b
-APP reactive zones in the high-overpressure brain sections
compared to medium overpressure and sham brain sections.
b
-APP
reactive zones were reminiscent of Amyloid
b
staining in Alzheimer’s.
Also observed was elevated astrocyte counts in both the blast groups. A
significant number of microglia were also observed in medium pressure
compared to sham. Our findings support the presence of prominent
axonal injury and
b
-APP reactive immunoreactive zones in these frontal
cortical regions following primary blast exposure. Prominent astrocytic
and microglial proliferation also suggests potential inflammatory
changes. These findings suggest a putative role for an altered neuroglial
homeostasis in the etiology of primary blast induced neurotrauma.
Keywords: Swine, Primary blast induced brain injury, Open field
blast,
b
-APP-beta amyloid precursor protein, Astrocytic and micro-
glial proliferation,
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