Typical MRI examinations focus on the evaluation of anatomy and detection of pathology. UCSD researchers are demonstrating how MRI can be used for evaluating tissue function. Techniques such as Functional MRI (fMRI), diffusion imaging, perfusion imaging, and MR Spectroscopy (MRS) are methods for evaluating tissue function.
The UCSD/Tenet Magnetic Resonance Institute also conducts clinical trials and collaborative research studies with local Neurologists, Neurosurgeons, Internal Medicine physicians, and Orthopedic Surgeons.
Functional MRI (fMRI)
Whenever we use our brains, neurons and supporting structures require oxygen and nutrients to provide energy for optimal brain function. Blood flow changes are linked with brain activation and can be measured using special MRI techniques. Whenever we perform an activity such as moving our fingers or opening and closing our hands, there is increased blood flow to the motor area of the brain. In fact, this flow increase exceeds the actual demand for oxygen. This increase of oxygenated blood relative to de-oxygenated blood results in subtle changes in MRI signal in comparison to the pre-activity state. This small change in MRI signal can be detected using ultra-fast Echo Planar Imaging (EPI) techniques. The difference between the pre-activity state and active state is mapped onto a high- resolution image. fMRI allows mapping of active areas of the brain during a wide range motor, sensory, and cognitive tasks. By mapping these patterns of brain activation, researchers hope to gain better understanding of neurological and psychological deficits such as Alzheimer’s disease, schizophrenia, autism, and patients with brain tumors.
Cerebral Blood Flow Imaging
The fMRI technique maps patterns of activation in the human brain based on changes in blood oxygenation. In addition, arterial spin labeling (ASL) techniques make possible direct imaging of blood flow in the brain. With this method arterial blood is magnetically tagged before it reaches a particular section of the brain. After waiting for the tagged blood to be delivered, an image is acquired. By subtracting two images, one with tagging and one without, an image of blood delivered to each region of the brain is calculated. The ASL technique can be used to map activations, like the fMRI technique. However, the ASL technique also reveals blood flow changes in pathological conditions, such as stroke.
Subtle fluid changes in the brain are seen in various disease states. Routine MRI is sensitive to these fluid changes and has improved medical treatment since its clinical inception. Diffusion imaging uses special manipulation of the magnetic field that allows the detection of brain fluid changes that may not be apparent on routine MRI images. Diffusion imaging aids in the early detection of stroke injury by differentiating the amount of brain tissue permanently damaged during a stroke from potentially recoverable brain tissue.
Perfusion imaging uses MRI contrast media (Gd-DTPA) to enhance damaged areas of the brain. Using both diffusion and perfusion imaging will help differentiate an ischemic stroke versus a hemorrhagic stroke. Perfusion imaging will determine if a stroke patient is a candidate for receiving new anti-coagulant drugs designed for reversing stroke symptoms. Hemorrhagic stroke patients are not candidates for receiving new anti-coagulant drugs.
Using magnetic resonance for the spectroscopic evaluation of chemical substances has been performed long before MRI became utilized for the evaluation of anatomy and pathology. MR Spectroscopy evaluates the chemical make-up of the brain without having to remove any tissue. This is extremely useful for studying metabolic disorders of the brain, differentiating changes in radiation necrosis versus recurrent brain tumor, and evaluating demyelination changes in the white matter or temporal lobes on patients with seizures.