72
L. E. Bilston
in internal damage to the brain. At the other end of the loading rate spectrum lie
neurostructural conditions such as hydrocephalus, where very slow dilatation of
the ventricles deep within the brain, often due to obstruction of a CSF outflow
pathway, compresses the surrounding brain tissue. Either slow or fast loading
can lead to neural injury and neurological and/or cognitive dysfunction. Brain
tissue mechanical behaviour has also been suggested to vary in some disease
conditions [2–5], and noninvasive methods of measuring tissue properties in vivo
could potentially be useful for discriminating between conditions that have similar
symptoms and imaging appearance, but different treatment outcomes. An example
of this is discriminating between normal pressure hydrocephalus, which responds
well to surgical shunt placement, and cerebral atrophy due to other neurological
disorders which does not [6, 7].
Another key driver for research aimed at understanding the fundamental biomechanical response of brain tissue is to provide high-quality experimental data
to allow for development of mathematical and computational models of brain
behaviour. This includes development of accurate constitutive models of brain
tissue behaviour, relevant to the problem being studied, and also to allow finite
element and other computational models to accurately simulate the brain response to
complex loading conditions. Such simulations might include analysis of traumatic
brain injury mechanisms and tissue injury thresholds, simulation of brain diseases
that have a mechanical component (e.g. hydrocephalus), and simulation of surgical
procedures for surgical planning or surgical training systems.
Brain tissue mechanics have become an increasing focus of research in the last
couple of decades, in part due to emerging methods for measuring in vivo brain
properties and associations between changes in brain mechanics and a variety of
neurological disorders.
In this chapter, the fundamental viscoelastic properties of brain tissue will be
critically reviewed, and limitations of the current state of knowledge and directions
for future research will be identified.
4.2 Shear Properties of Brain Tissue
Interest in the shear response of brain tissue arose from early studies by Holbourn
[8] who hypothesised that diffuse axonal damage seen in the brain parenchyma after
traumatic brain injury occurred as a result of rotational shear within the brain. This
was further substantiated in the 1980s by Thibault and Gennarelli’s experimental
work with non-human primates [9].
Methodological issues have played a major role in the apparently disparate
shear properties reported for brain tissue in the literature, and only in the late
1990s did the rigour of rheology begin to be applied to measurement of shear
properties of brain tissue. Much of the large disparity between the previously
reported data can be explained in the light of more rigorous approaches to control
of sample preparation, test conditions, and the use of standard rheological test
L. E. Bilston
in internal damage to the brain. At the other end of the loading rate spectrum lie
neurostructural conditions such as hydrocephalus, where very slow dilatation of
the ventricles deep within the brain, often due to obstruction of a CSF outflow
pathway, compresses the surrounding brain tissue. Either slow or fast loading
can lead to neural injury and neurological and/or cognitive dysfunction. Brain
tissue mechanical behaviour has also been suggested to vary in some disease
conditions [2–5], and noninvasive methods of measuring tissue properties in vivo
could potentially be useful for discriminating between conditions that have similar
symptoms and imaging appearance, but different treatment outcomes. An example
of this is discriminating between normal pressure hydrocephalus, which responds
well to surgical shunt placement, and cerebral atrophy due to other neurological
disorders which does not [6, 7].
Another key driver for research aimed at understanding the fundamental biomechanical response of brain tissue is to provide high-quality experimental data
to allow for development of mathematical and computational models of brain
behaviour. This includes development of accurate constitutive models of brain
tissue behaviour, relevant to the problem being studied, and also to allow finite
element and other computational models to accurately simulate the brain response to
complex loading conditions. Such simulations might include analysis of traumatic
brain injury mechanisms and tissue injury thresholds, simulation of brain diseases
that have a mechanical component (e.g. hydrocephalus), and simulation of surgical
procedures for surgical planning or surgical training systems.
Brain tissue mechanics have become an increasing focus of research in the last
couple of decades, in part due to emerging methods for measuring in vivo brain
properties and associations between changes in brain mechanics and a variety of
neurological disorders.
In this chapter, the fundamental viscoelastic properties of brain tissue will be
critically reviewed, and limitations of the current state of knowledge and directions
for future research will be identified.
4.2 Shear Properties of Brain Tissue
Interest in the shear response of brain tissue arose from early studies by Holbourn
[8] who hypothesised that diffuse axonal damage seen in the brain parenchyma after
traumatic brain injury occurred as a result of rotational shear within the brain. This
was further substantiated in the 1980s by Thibault and Gennarelli’s experimental
work with non-human primates [9].
Methodological issues have played a major role in the apparently disparate
shear properties reported for brain tissue in the literature, and only in the late
1990s did the rigour of rheology begin to be applied to measurement of shear
properties of brain tissue. Much of the large disparity between the previously
reported data can be explained in the light of more rigorous approaches to control
of sample preparation, test conditions, and the use of standard rheological test