Neuroimaging Flashcards
Computed tomography (CT)
structural imaging
X-ray
Pro: Detects gross abnormalities for acute care (skull fractures, hemorrhage, mass effect
Con: Less effect detecting white matter changes (plaques/myelin loss in MS
Risk: small amounts of radiation
Magnetic resonance imaging (MRI)
structural imaging
Radiofrequencies to generate electromagnetic reaction of hydrogen proteins in water molecules
T1 scan: greater anatomical detail but less tissue contrast (gray matter = gray, white matter = white)
T2 scan: sensitive to detecting damaged vs intact tissues; helpful for lesion identification (white matter = grey, axonal injury = brighter)
Pro: highly detailed imagines of brain anatomy, including connecting fibers
Repeat use b/c does not use radiation
Con: noisy, claustrophobia, cannot use if implanted devices or residual metal fragments from accident
Diffusion tensor imaging (DTI)
structural imaging
Examines white matter integrity and white matter tracts by detecting directional movements of water molecules
Functional imaging
Measures changes in brain activity by measuring changes in blood flow and oxygen
“Resting” - images acquired during static or non-activated conditions
*there are multiple brain networks active despite non-task-engaged state
“Activated” - images acquired during engagement in a cognitive and motor task
Single-Photon Emission Computed Tomography (SPECT)
functional imaging
Examines regional changes in cerebral activity or brain chemistry through the use and detection of radioactive tracer flow or receptor-binding radioisotopes
Radioisotopes are absorbed by glia (brain cells) and remain in greater concentration in more active regions of the brain. As they undergo decay, they emit radioactive particles, which are detected to generate a computerized reconstruction.
Pro: more available than PET or fMRI
Positron Emission Tomography (PET)
functional imaging
Examines metabolic activity in brain cells engaged in cognitive tasks using radioisotope tracers
Can be useful in the differential diagnosis of dementia (AD vs FTD) due to differing patterns of abnormal cerebral (glucose) metabolism
Pro: greater spatial resolution than SPECT
Con: expense
Functional Magnetic Resonance Imaging (fMRI)
functional imaging
Examines regional changes in brain activity - neural activity is associated with blood flow to that region and the localized surplus of oxyhemoglobin relative to deoxyhemoglobin
fMRI for clinical purposes has been limited mostly to presurgical mapping for epilepsy surgeries and tumor resections.
Research: fMRI is reliable when there is strong left-lateralized language. The Wada test is warranted when fMRI fails to show clear left-lateralization.
Pro: superior resolution to SPECT and PET
Con: technical limitations
Electroencephalography (EEG)
Electrophysiological study
Monitors brain electrical activity (voltage fluctuations) along the scalp.
Purpose: differentiate epileptic seizures from other types of events (e.g., nonepileptic seizures, fainting, or subcortical disorders).
Waveforms:
Alpha - manifests when the patient is relaxed with eyes closed and ablated by eye opening
Beta - dominant rhythm in patients who are alert, anxious, or have their eyes open
Theta - are observed in children and during sleep at any age
Delta - are observed during sleep across all age groups and are normally the dominant rhythm in infants
Evoked Potentials (EPs)
Electrophysiological study
Involves the noninvasive stimulation of afferent pathways (visual, auditory, somatosensory/skin)
Frequently used to detect and localize lesions in the CNS (e.g., MS) and other CNS disorder (AIDS, neurosyphilis) - also been used to assess prognosis after CNS trauma or hypoxia and to assist during intraoperative monitoring.
Cerebral Arteriography (a.k.a. angiography)
invasive exam
involves injection of an iodine-based contrast via catheter inserted into the femoral or brachial artery and threaded up the aortic arch.
Pro: provides excellent characterization of arteriovenous malformation (tangle of blood vessels), aneurysms (bulge in blood vessel), and cerebral venous sinus thrombosis (blood clot).
Con: complications include stroke, an allergic reaction to the contrast, and thrombosis or embolism formation.
Intracarotid Sodium Amobarbital Procedure (Wada testing)
invasive exam
Injecting sodium amobarbital via catheter to produce a brief period of anesthesia of the ipsilateral hemisphere
Testing of various functions such as language, memory, movement is conducted to determine capabilities of one hemisphere while the other is anesthetized.
Testing is performed for presurgical candidates with epilepsy to determine hemispheric dominance for language and potential postoperative cognitive losses.
Computed Tomographic Angiography (CTA)
invasive exam
visualize arterial and venous vessels.
Assists in evaluation of conditions such as carotid stenosis, intra and extracranial atherosclerosis, and aneurysms.
Con: reduced sensitivity for small aneurysms and may not reveal disease of small vessels.
Lumbar Puncture (spinal tap)
invasive exam
Provides direct access to the subarachnoid space to obtain samples of CSF, measure CSF pressure, or to remove CSF.
Needle inserted below spinal cord (usually between L4 and L5)
CSF fluid is inspected for blood or bacteria to assess for infectious or inflammatory disorders, sub-arachnoid hemorrhage and abnormalities of intracranial pressure that affect CSF.
Also allows for detection of biomarkers, such as levels of tau for AD
Lumbar Puncture (spinal tap)
invasive exam
Provides direct access to the subarachnoid space to obtain samples of CSF, measure CSF pressure, or to remove CSF.
Needle inserted below spinal cord (usually between L4 and L5)
CSF fluid is inspected for blood or bacteria to assess for infectious or inflammatory disorders, sub-arachnoid hemorrhage and abnormalities of intracranial pressure that affect CSF.
Also allows for detection of biomarkers, such as levels of tau for AD
Magnetic resonance angiogram
Used to evaluate for stenosis, occlusions, and aneurysms
