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E. Liebenthal and T. Singhal
3.1.1 Magnetic Resonance Imaging (MRI)-Based Brain
Imaging Techniques
3.1.1.1 Magnetic Resonance Imaging (MRI)
Magnetic resonance imaging (MRI) provides good contrast resolution between
different soft tissues, making it particularly useful in the brain. The discoveries that
led to the development of modern MRI were first reported in the 1970s [62, 74], and
since its introduction as a diagnostic tool in the 1980s, MRI has become the main
modality for structural neuroimaging. The advent of higher-field magnets (3 Tesla)
has resulted in standard imaging at an exquisite spatial resolution of approximately 1
mm 3 , permitting visualisation of fine anatomic details at clinically acceptable short
acquisition times. MRI is vastly superior to other structural imaging methods such
as X-ray, computed tomography (CT), and ultrasound, in terms of spatial resolution
and the delineation of tumours [4]. In addition, different from X-ray and CT which
involve ionising radiation, MRI is based on noninvasive radio-frequency excitation
of biological molecules with magnetic properties.
3.1.1.2 Functional Magnetic Resonance Imaging (fMRI)
Functional magnetic resonance imaging (fMRI) is used to map function in the
entire brain noninvasively. fMRI is an indirect measure that is based on the premise
of a relationship between local changes in neural activity and cerebral blood
dynamics [70, 71]. fMRI using the blood oxygenation level-dependent (BOLD)
contrast is a method to measure local changes in the concentration of paramagnetic
deoxyhaemoglobin that are associated with an increase in blood flow to active
regions in the brain [58, 89]. First reports of fMRI in humans demonstrated that
visual stimulation produces a detectable transient increase in the intensity of water
proton magnetic resonance signal in the primary visual cortex [12, 90]. Similar
increases in fMRI signal were found in the motor cortex during finger movement
[9]. The spatial resolution of fMRI is high, typically ranging 3–5 mm for most
common applications. But the temporal resolution is low, with a mean rise time
for signal change of 4–6 seconds, approximately two orders of magnitude slower
than the underlying neural activity.
fMRI has transformed research in cognitive neuroscience, as well as clinical
applications such as presurgical mapping of eloquent cortex, because of the
low invasiveness, imaging of function in the entire brain with exquisite spatial
resolution, and relatively wide availability [33]. Two decades of fMRI research in
cognitive neuroscience have highlighted the distributed and individual (related to
learning and memory or caused by pathological changes) nature of brain function,
largely contradicting the classic view emerging form earlier lesion studies of a
fixed and focal relationship between brain anatomy and function [78]. The modern
understanding of the organisation of cognitive brain functions emphasises the value
of fMRI mapping for identifying neural network systems in individual patients and
E. Liebenthal and T. Singhal
3.1.1 Magnetic Resonance Imaging (MRI)-Based Brain
Imaging Techniques
3.1.1.1 Magnetic Resonance Imaging (MRI)
Magnetic resonance imaging (MRI) provides good contrast resolution between
different soft tissues, making it particularly useful in the brain. The discoveries that
led to the development of modern MRI were first reported in the 1970s [62, 74], and
since its introduction as a diagnostic tool in the 1980s, MRI has become the main
modality for structural neuroimaging. The advent of higher-field magnets (3 Tesla)
has resulted in standard imaging at an exquisite spatial resolution of approximately 1
mm 3 , permitting visualisation of fine anatomic details at clinically acceptable short
acquisition times. MRI is vastly superior to other structural imaging methods such
as X-ray, computed tomography (CT), and ultrasound, in terms of spatial resolution
and the delineation of tumours [4]. In addition, different from X-ray and CT which
involve ionising radiation, MRI is based on noninvasive radio-frequency excitation
of biological molecules with magnetic properties.
3.1.1.2 Functional Magnetic Resonance Imaging (fMRI)
Functional magnetic resonance imaging (fMRI) is used to map function in the
entire brain noninvasively. fMRI is an indirect measure that is based on the premise
of a relationship between local changes in neural activity and cerebral blood
dynamics [70, 71]. fMRI using the blood oxygenation level-dependent (BOLD)
contrast is a method to measure local changes in the concentration of paramagnetic
deoxyhaemoglobin that are associated with an increase in blood flow to active
regions in the brain [58, 89]. First reports of fMRI in humans demonstrated that
visual stimulation produces a detectable transient increase in the intensity of water
proton magnetic resonance signal in the primary visual cortex [12, 90]. Similar
increases in fMRI signal were found in the motor cortex during finger movement
[9]. The spatial resolution of fMRI is high, typically ranging 3–5 mm for most
common applications. But the temporal resolution is low, with a mean rise time
for signal change of 4–6 seconds, approximately two orders of magnitude slower
than the underlying neural activity.
fMRI has transformed research in cognitive neuroscience, as well as clinical
applications such as presurgical mapping of eloquent cortex, because of the
low invasiveness, imaging of function in the entire brain with exquisite spatial
resolution, and relatively wide availability [33]. Two decades of fMRI research in
cognitive neuroscience have highlighted the distributed and individual (related to
learning and memory or caused by pathological changes) nature of brain function,
largely contradicting the classic view emerging form earlier lesion studies of a
fixed and focal relationship between brain anatomy and function [78]. The modern
understanding of the organisation of cognitive brain functions emphasises the value
of fMRI mapping for identifying neural network systems in individual patients and