CH 6 Neuroimaging studies Flashcards
X Rays
rapid exam of skull injuries
CT stands for
computed tomography
What is CT
x-ray beam rotated around pt’s head to take many views
rays absorbed based on density
greatest absorption occurs for the densest structures (hyperdense) like bones, fresh blood, calcifications
Hyperdense structures are brighter or lighter in color?
lighter
Example of Hypodense structures on CT?
air and fat
Hypodense structures are brighter or lighter in color?
darker
Advantage of CT
detect gross abnormality in acute care
useful for skull fracture, hemorrhage, mass effect
Disadvantage of CT
less effective at detecting white matter changes (e.g. plaques in MS, microvascular ischemic changes) or refine differential diagnosis (e.g. tumor, mass)
Risks of CT
small amount of ionizing radiation
allergic reaction to iodine based contrast media
MRI stands for
Magnetic Resonance Imaging
How is MRI done
generate high resolution anatomic images of brain structure
radiofrequency pulses generate electromagnetic reaction of hydrogen protons in water molecules. When pulses stop, protons return to original alignment, then emission of signals detected by scanner to construct image
What do T1 and T2 stand for
time constants
T1
demonstrates greater anatomic detail but less tissue contrast
T2
enhanced contrast and more sensitive to detecting damaged vs intact tissue
more useful for lesion identification
FLAIR
fluid attenuated inversion recovery
allows for representation of even greater contrast between normal and pathological issue
Advantages of MRI
highly detailed images of brain anatomy
detection of low contrast or small lesions (e.g. MS, AVM, low grade astrocytoma)
Diffusion Weighted MRI (DWI)
using diffusion of water molecules to generate contrast in MR images
When is DWI used
stroke imaging, white matter diseases, oncology
Why is DWI used over conventional imaging?
allows collection of info about molecular activity and cellular function
sensitive to microstructural changes
detect abnormalities like white matter disease
(e.g. stroke during first few hours of onset prior to detectability on standard MRI)
Perfusion Weighted MRI
infer how blood travels through brain’s vasculature through the use of contrast medium or endogenous blood flow marker
When is Perfusion Weighted MRI used?
diagnosis and imaging of brain tumors which exhibit unusual diffusion due to mass effect, modulated metabolism, pathological leakage across blood brain barrier
What does Perfusion Weighted MRI assess?
assessment of hemodynamic parameters
e.g. cerebral blood volume, cerebral blood flow, mean transit time, and time to peak
Susceptibility Weighted imaging
sensitive to detecting small amounts of blood products and calcium that may be undectatable with other MRI sequences
Susceptibility weighted imaging advantage
useful for small lesion
ability to detect more subtle TBIs and hemorrhages in cerebral amyloid angiopathy
Diffusion Tensor Imaging (DTI)
examine white matter integrity and white matter tracts by detecting the directional movements of water molecules
How does DTI assess
generates fractional ansiotropy (FA) value
FA value in DTI (high vs low)
high FA value in very organized densely myelinated regions of the brain (e.g. corpus callosum, pyramidal tracts)
Low FA value in less organized, less myelinated, or state of edema, injury or inflammation
Magnetic Resonance Spectroscopy (MRS)
MRI method to localize and characterize brain based biomarkers
How is MRS different from conventional MRI
can image endogenous biological markers such as creatinine, NAA, glutamate
can detect brain cell loss in degenerative diseases such as AD and MS
Magnetic Resonance Angiography (MRA)
generate images of arteries to evaluate stenosis, occlusions, aneurysms
Advantages of MRA
non invasive nature
Disadvantages of MRA
poorer spatial resolution
less sensitivity to vessels with slower blood flow
lengthier procedure time than CT angiography
2 categories of Functional imaging
resting
activated
What is Single photon Emission computer tomography (SPECT)
examines regional changes in cerebral activity or brain chemistry through the use and detection of tracer flow or receptor binding isotopes
What is SPECT for
study regional blood flow (rCBF) which is correlated with brain activity
SPECT markers have been developed for specific types of neuropathology such as
beta amyloid and TAU
Advantages of SPECT
less extensive tech requirements
radio tracers are stable
Position Emission Tomography (PET)
examines glucose utilization with radiostopes
examines metabolic activity in brain cells engaged in cognitive tasks
How does PET assess
utilizes intravenous tracers (FDG) nad oxygen 15 ti characterize resting regional brain metabolism
How is PET useful
differential diagnosis of dementia due to differing patterns of abnormal cerebral metabolism
How does PET help with diagnosis of AD?
in AD, PET imaging reveals bilaterally reduced regional glucose metabolism in posterior temporoparietal cortices in addition to anterior and mesial temporal lobes
How does PET help with diagnosis of FTD?
in FTD, PET imaging shows hypometabolism mostly in the frontal and anterior temporal cortices
PET advantage
greater spatial resolution than SPECT
PET disadvantage
expense
fMRI
- 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 results in signal intensity
BOLD effect
blood oxygen level dependent effect
measures changes in blood flow by detecting changes in intravascular oxyhemoglobin concentration
Use of fMRI mostly for?
presurgical mapping for epilepsy surgeries and tumor resections
advantages of fMRI
no tracers, radiosotopes, contrast agents
superior to SPECT and PET
Electrophysiological Studies
EEG
EEG
- monitor brain electrical activity along the scalp
- records the sum of rhythmical activitiy of thousands of neurons
What is EEG used for
to differentiate epileptic seizures from other types of events (non epileptic, fainting, subcortical d/o)
dx of coma, determination of brain death, polysomnography, monitoring anesthesia depth
Repetitive slow wave complexes over temporal lobe with cerebral dysfunction indicates
herpes simplex encephalitis
EEG wave forms are classified according to what?
frequency
amplitude
shape
scalp region
Alpha waves - how many Hz?
8-12 Hz waveforms
Alpha waves are observed in which age groups?
all age groups, most common in adults
When are alpha amplitude manifested?
patient relaxed with eyes closed and ablated by eye opening
Where are alpha waves located?
bilateral posterior regions
Beta waves - how many Hz?
12-30 Hz
Beta waves are observed in which age groups?
all age groups
When are beta waves manifested?
it is the dominant rhythm in patients who are alert, anxious, or have their eyes open
Describe beta waves distribution
symmetrical distribution
most evident frontally
Beta activity can be enhanced under what condition
sedating drugs (e.g. benzo, barbiturates)
Theta waves - how many Hz?
4-7 Hz
Theta waves are observed in which age groups?
children
any age group during sleep
When are theta waves observed?
transiently observed during normal wakefulness
prominently observed during drowsiness
Delta waves - how many Hz?
up to 4 Hz
When are delta waves observed?
during sleep across all age groups
normally the dominant rhythm in infants
Where are delta waves observed?
frontally in adults and posteriorly in children
What are evoked potentials (EP)?
involves the noninvasive stimulation of afferent pathways
Visual EP tests
present fixed visual pattern to each eye and record electrical activity
Auditory EP tests
administer repetitive clicks to each ear
Somatosensory EP test
use mechanical or brief electrical stimulation to skin
EP is often used for what?
detect and localize lesions in the CNS
monitor prognosis after CNS trauma or hypoxia
EMG
recording electrical activity in specific muscles and peripheral nerves
Needle EMG
insert needle electrode into muscle
nerve conduction studies utilize electrodes taped to the skin to measures specific waveforms generated
MEG/MSI
detect minute magnetic fields generated by neuronal activity
when neuronal synapse becomes active, there is current flow across membranes that can be recorded
Cerebral Anteriography (angiography)
injection of iodine-based contrast into the cerebrovascular via catheter inserted into femoral or brachial artery and threaded up the aortic arch
What is angiography best used for?
characterization of AVM, aneurysm, cerebral venous sinus thrombosis
differential dx of tumor that produce a stain as a result of neovascularization
coil embolization of aneurysm
performed with angiography
Wada testing
inject sodium amobarbital into cerebrovasculature via angiographically guided catheter to produce brief period of anesthsia of ipsilateral hemisphere
purpose of Wada testing
Testing of language, memory, movement is conducted to determine capabilities of one hemisphere while the other is anesthetized
Testing performed for presurgical candidates with epilepsy to determine hemispheric dominance for language and potential post op loss
CTA - computed tomographic angiography
visualize arterial and venous vessel
requires combo of IV injection of radiocontrast and CT scan
Function of CTA
evaluate carotid stenosis, intra and extra cranial atheroschlerosis, aneurysms
Advantage of CTA
high quality image in 5-10 sec
useful for dx and f/u of cerebrovascular disease
image less impacted by movement
Disadvantages of CTA
reduced sensitivity for aneurysm smaller than 3mm
not reveal plaque ulceration or small vessel disease
Lumbar punture
spinal tap
provides access to subacrachnoid space to obtain samples of CSF, CSF pressure, or remove CSF
detection of biomarkers (e.g. tau)
How is lumbar puncture performed
insert needle below spinal cord (L4/L5)
inspect CSF fluid for blood or bacterial to assess infectious or inflammatory disorders, sub-arachnoid hemorrhage and abnormalities of intracranial pressure that affect CSF
Awake and alert waves before falling asleep?
BATS
Beta
Alpha
Waves observed in Non Rem Stage 3 sleep
Drink
- Delta
Waves observed REM sleep
Blood = Beta
Waves in non Rem sleep stage 1
baTS
Theta
sleep spindles/ k complex
