Epilepsy Awareness Program - EEG vs MRI, fMRI and PET
Electroencephalography (EEG) is a non-invasive test for epilepsy during which several electrodes are placed on a patient's scalp to record electrical impulses from the brain (brain waves). It is sometimes called a brain wave test, used for testing patients with epilepsy, a brain tumor, a brain abscess, brain trauma, subdural hematoma, meningitis, encephalitis, stroke or congenital defects of the brain.
It is performed by using a device that measures the fluctuations and patterns in electrical processes within the brain.
More information on EEG
MRI is a magnetic resonance imaging: the use of nuclear magnetic resonance of protons to produce proton density images. It is a type of diagnostic imaging that uses electromagnetic imaging and allows evaluation of tissues and fluid in addition to bone. This imaging providing two dimensional cuts through the body part being study which allows a physician to develop a three dimensional sense of the anatomy of that part. Often used to study the brain and spine as well as joints.
It is primarily used in medical imaging to visualise the structure and function of the body. It provides detailed images of the body in any plane.
MRI may detect certain lesions (diseased tissue) in the brain that cause seizures. MRI also helps specialists diagnose the causes of epilepsy and evaluate potential candidates for surgery.
Brain abnormalities may be subtle. Specialized MRI scanning may detect asymmetries (dissimilar corresponding parts on opposite sides that are normally alike) in the brain that indicate the side of the brain where seizures begin.
Functional magnetic resonance imaging: a form of magnetic resonance imaging of the brain that registers blood flow to functioning areas of the brain.
It is a relatively new MRI technique that studies brain function. Using fMRI technology, scientists can determine which part of the central nervous system (CNS: brain and spinal cord) is active during a given task by tracking blood oxygen levels in the brain. Brain regions that are active require more oxygen. Oxygen is delivered by increasing the blood flow to these active brain regions. Scientists compare the differences in blood flow between a resting condition and an active condition, such as thinking, seeing, touching, or hearing, to find regions that are associated with one task and not the other.
Positron emission tomography (PET) is a nuclear medicine imaging technique which produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer), which is introduced into the body on a biologically active molecule. Images of tracer concentration in 3-dimensional or 4-dimensional space (the 4th dimension being time) within the body are then reconstructed by computer analysis. In modern scanners, this reconstruction is often accomplished with the aid of a CT X-ray scan performed on the patient during the same session, in the same machine.
A PET scan analyzes the amount of glucose, or sugar uptake by the brain. One would inject in a glucose substitute that has a label on it, and then take images of the brain during a period of time shortly after the seizure. The PET scan allows us to look at regions of the brain that are either hypermetabolic i.e. using a lot of sugar, or parts of the brain that are hypometabolic i.e. using very little sugar. It turns out that for Temporal Lobe Epilepsy, the temporal lobe shows hypometabolism.
EEG vs fMRI and PET:
EEG has several strong points as a tool for exploring brain activity. EEG's can detect changes within a millisecond timeframe, excellent considering an action potential takes approximately 0.5-130 milliseconds to propagate across a single neuron, depending on the type of neuron. Other methods of looking at brain activity, such as PET and fMRI have time resolution between seconds and minutes. EEG measures the brain's electrical activity directly, while other methods record changes in blood flow (e.g., SPECT, fMRI) or metabolic activity (e.g., PET), which are indirect markers of brain electrical activity. EEG can be used simultaneously with fMRI so that high-temporal-resolution data can be recorded at the same time as high-spatial-resolution data, however, since the data derived from each occurs over a different time course, the data sets do not necessarily represent the exact same brain activity. There are technical difficulties associated with combining these two modalities, including the need to remove the MRI gradient artifact present during MRI acquisition and the ballistocardiographic artifact (resulting from the pulsatile motion of blood and tissue) from the EEG. Furthermore, currents can be induced in moving EEG electrode wires due to the magnetic field of the MRI.
For More informatio: Download What's the difference: PET vs. SPECT, etc? - Source: The Academy for Lifelong Learning
See Also: Epilepsy Health Corner
See Also: Neurophysiology Health Corner