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Imaging Techniques The MR Research Laboratory is equipped to collect a variety of data types, both qualitative and quantitative. Several of the data acquisition techniques used in the laboratory are described below.
Conventional Structural MRI
In clinical practice, MRI is primarily used for
the acquisition of structural images that provide cross sectional views of
internal structures. All
three MR systems in the laboratory can
be used to acquire structural anatomic
images. Structural images are used by
researchers for the establishment of diagnoses, measurement of
tissue volumes, monitoring the effects of treatment,
and can serve as localization references for
other types of information that can be acquired
with MR, such as localized spectroscopy.
MR Angiography
MR angiography (MRA) provides a clear view of blood vessels throughout the body
non-invasively.
MRA techniques use physical properties of
blood flow to selectively enhance the appearance
of arteries and veins. Conventional MRA
often does not require injection of a contrast
agent prior to imaging. Contrast-enhanced
MRA can be used in select situations to provide detailed vessel information useful in research with specific vascular interests and needs.
Functional MRI
With functional MRI (fMRI), rapid dynamic images are acquired at a rate of approximately
1 image every 100 milliseconds. The images are used to derive information
about regional changes in blood flow and blood oxygenation to identify areas of the
brain associated with specific tasks. This non-invasive technique requires no injection
and is highly sensitive to the brain’s response to motor, sensory and cognitive tasks.
With this technique, investigators throughout the UW community utilize the MR Research Laboratory resources
to study a variety of neurodevelopmental and neurodegenerative disorders, including dyslexia, autism, HIV dementia, fetal alcohol syndrome,
traumatic brain injury, stroke and multiple sclerosis.
MR Spectroscopy
Magnetic resonance spectroscopy (MRS) allows scientists to detect, compare, and
quantify the concentration of a variety of biological metabolites. MR Research
Laboratory systems are used to perform these measurements in very specific locations
in the body for sample sizes down to the order of approximately 1 cubic centimeter of
tissue in vivo. Techniques have also been developed in the lab to calculate the spatial
distribution of different metabolites across cross sections of tissue in the brain.
Functional MR Spectroscopy
MR Spectroscopy can be used to measure dynamic
changes in chemical concentrations over time. This
technique is called functional MR spectroscopy
(fMRS). One application of this technique is
recording changes in chemical concentrations in the
brain as a subject performs a task, using methodology
analogous to that used for fMRI.
Perfusion Imaging
MR can also be used to generate images that measure
blood flow through the brain capillaries, also known as
tissue perfusion. This can be done using either a
contrast agent or with a non-invasive MR technique
called arterial spin labeling (ASL).
CSF Flow Imaging
Quantitative measurements of
the velocity and volume of
cerebral spinal fluid (CSF) flow
can be obtained using special
MR acquisition and data analysis
techniques. These methods
allow scientists to dynamically
view CSF flow and to calculate
both the speed and direction as
it changes due to vascular pulsation
and respiration. Specific flow measurements in
regions of interest are useful for evaluating
abnormalities in the spaces in and surrounding the
brain and spinal cord, such as Chiari malformation or arachnoid cysts.
Diffusion Tensor Imaging (DTI)
Diffusion tensor imaging (DTI) is a MRI
technique that enables the measurement of the restricted diffusion of water
in tissue. The principal application is in the imaging of white matter where
the location, orientation, and anisotropy of the tracts can be measured. The
architecture of the axons in parallel bundles, and their myelin sheaths,
facilitate the diffusion of the water molecules preferentially along the dominant direction. Such preferentially oriented diffusion is called anisotropic diffusion.
Scientists have used DTI to study white matter fiber tract
differences between dyslexic and normal readers.
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