Neuroimaging, a field at the intersection of neuroscience and technology, provides invaluable insights into the intricate workings of the human brain. In this exploration, we look into various types of neuroimaging techniques, each offering a unique perspective on brain structure, function, and pathology. The following tests compliment EEG recordings to provide comprehensive understanding into the why and where of seizure origins.
SISCOM: Shedding Light on Seizure Onset Zones
A special protocol known as SISCOM has been developed to obtain specific information about the origin of seizures in the brain. This protocol compares blood flow during and between seizures and superimposes those images on an MRI.
Referred to as Subtraction Ictal SPECT Co-registered to MRI (SISCOM), this protocol is performed in certain epilepsy centers during an admission in the Epilepsy Monitoring Unit. The obtained information is considered along with EEG data and MRI to determine the seizure onset zone.
MEG: Unveiling Magnetic Fields of Brain Activity
Magnetoencephalography (MEG) is a non-invasive test that measures the magnetic fields produced by brain electrical activity. MEG is performed to map brain function, including centers of sensory, motor, language, and memory activities. It is particularly useful in identifying the precise location of the source of epileptic seizures. Brain cells interact by generating tiny electrical voltages, creating electrical currents throughout the brain. The MEG helmet, equipped with specialized sensors, detects and records the magnetic fields produced by these electrical activities.
SPECT: Mapping Blood Flow for Diagnosis
Single Photon Emission Computed Tomography (SPECT) scans show how blood flows to tissues and organs (perfusion). SPECT is valuable in diagnosing seizures, strokes, and tumors in the spine. It involves nuclear imaging, integrating CT scan and a radioactive tracer. The tracer emits gamma rays, displaying in CT cross sections. These cross sections are then reconstructed to show a 3D image.
Ictal SPECT: Performed in conjunction with EEG to locate origin of seizures. EEG is monitored and upon start of ictal activity the patient receives an injection of the tracer and SPECT imaging is performed.
PET: Unraveling Metabolism with Positron Emission Tomography
PET scans reveal the brain's use of oxygen or glucose, indicating hyper/hypometabolism. A tracer is injected, and PET records how it travels through the brain. Colors differentiate higher or lower areas of oxygen and glucose. PET scans are relatively expensive and not readily available compared to other imaging techniques.
MRI: Unprecedented Detail in Brain Imaging
Magnetic Resonance Imaging (MRI) uses powerful magnetic fields and radio waves to produce detailed pictures of the brain. Currently, MRI is the most sensitive imaging test for the head, looking for structural causes of epilepsy, such as tumors or cavernous malformations. It can also identify conditions like temporal sclerosis, resulting from trauma.
fMRI: Mapping Brain Function in Action
Functional Magnetic Resonance Imaging (fMRI) measures the small changes in blood flow that occur with brain activity. fMRI is used to examine the functional anatomy of the brain, determining critical functions such as thought, speech, movement, and sensation. It aids in brain mapping and helps assess the effects of stroke, trauma, or degenerative diseases like Alzheimer's.
CT: Comprehensive Insight with Computed Tomography
Computed Tomography (CT) can identify atrophy, scar tissue, strokes, tumors, or abnormal blood vessels. CT scans, while informative, are not as effective at discriminating between gray matter and white matter compared to other imaging techniques.
Other Tests: WADA and TCD
Named after Dr. Juhn Wada, the intracarotid sodium amobarbital procedure (ISAP) evaluates how important each side of the brain is with respect to language and memory functions. The WADA test involves angiography to examine blood flow through the arteries. Sodium amobarbital is then injected to induce "sleep" in each hemisphere, during which the patient performs speech, memory, and other functions. Transcranial Doppler is a painless ultrasonography test that uses sound waves to detect blood flow in the brain. It is often used in diagnosing brain death.
Electrical Source Imaging (ESI): Integrating EEG and MRI
ESI is a technique that takes EEG data and projects it onto an MRI of the brain to show doctors where seizures are occurring.
As technology advances, neuroimaging continues to unlock the secrets of the brain, contributing to advancements in medical diagnostics and treatment planning. These techniques not only aid in understanding neurological conditions but also pave the way for innovative approaches to enhance brain health and function.