Biology Reference
In-Depth Information
Magnetic resonance imaging (MRI) is the method of choice to
evaluate brain ischemic lesion for three main reasons: first, it allows
a noninvasive follow-up of the lesion evolution in the same animal
along time, second, it allows to evaluate the lesion from minutes to
months post-ischemia; third, several imaging parameters, to be
functional or structural, can be acquired almost simultaneously. In
fact standard T2-weighted magnetic resonance imaging (T2WI) is
helpful and widely used in experimental research as in the evalua-
tion of patients with ischemic stroke. However, these imaging
modalities are useful at the chronic stage and should be used for
longitudinal evaluation. Diffusion-weighted magnetic resonance
imaging (DWI) that was validated using animal stroke models can
demonstrate ischemic brain regions within minutes after ischemia.
Furthermore, perfusion weighted imaging (PWI), is able to deter-
mine regions with reduced blood perfusion. The mismatch between
the area of diffusion abnormality and the area of perfusion abnor-
mality defines the ischemic penumbra. From a therapeutic point of
view, the ischemic penumbra might be defined as a target for neu-
roprotective and neuroregenerative treatments. If the apparent dif-
fusion coefficient evolves over time after stroke, the anisotropy also
experience changes. Diffusion tensor imaging allows analyzing the
evolution of anisotropy in the tissue. Since their development in
experimental research, these techniques have been extensively
applied to clinical investigations and clinical practice. Furthermore
the acquisition of T2*-weighted magnetic imaging and angiogra-
phy respectively allow the evaluation of potential hemorrhage and
the visualization of the occluded vessel. Those different approaches
are summarized in Fig. 3 .
3.2.2 Evaluation
of Ischemic Brain Injury
Magnetic Resonance
Imaging
As the ultimate goal for any therapeutic intervention in patients is
the recovery of functional deficits, to be sensorial, motor or cogni-
tive, the use of behavioral tests to assess the evolution of brain isch-
emia-induced deficits in animals is crucial ( 54 ). In general, these
behavioral tests need to be sensitive enough to detect weak deficits,
especially in the chronic stage as rodents are known to display a
rapid and pronounced functional recovery compared to humans.
Different tests could be used to evaluate post-ischemic impair-
ments. At the acute phase (i.e., during the first week following
stroke), one can assess the neurologic deficits through the use of
available neurological scales which include a battery of neurological
tests comprising the spontaneous activity, the symmetry in the move-
ment of limbs, the forepaw outstretching, the climbing, the body
proprioception and the response to vibrissae touch ( 55 ). Other sen-
sorimotor tests (accelerated rotarod test, corner test, adhesive
removal test, staircase test, beam walking test, etc.) and cognitive
tests (passive avoidance test, Morris water maze test, object recogni-
tion test, etc.) can be employed to assess both short- and long-term
deficits. These tests have been described elsewhere ( 54 ).
Neurologic De fi cits
Evaluation
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