Neuroimaging

Question 1

Computed Tomography (CT)

Answer 1

structural imaging

X-ray

Rays are absorbed based on densities (greatest absorptions occurs for the densest structures – hyperdense including bone, congealed blood, or other calcifications).

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

Question 2

Magnetic resonance imaging (MRI)

Answer 2

structural imaging
Radiofrequencies to generate electromagnetic reaction of hydrogen proteins in water molecules. When pulses are stopped, the protons return to original alignment, resulting in emission of electrical signals.

T1 scan: greater anatomical detail but less tissue contrast (gray matter = gray, white matter = white). Useful for lesion identification.

T2 scan: sensitive to detecting damaged vs intact tissues; helpful for lesion identification (white matter = grey, axonal injury = brighter). Used for cavitated lesions such as lacunar infarcts.

FLAIR (fluid attentuated inversion recovery): Representation of even greater contrast between normal and pathological tissue.

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

Question 3

Diffusion tensor imaging (DTI)

Answer 3

structural imaging
Examines white matter integrity and white matter tracts by detecting directional movements of water molecules.

Pro:
1. Can detect stroke during first few hours of onset prior to MRI due to discriminability of cytotoxic edema vs. vasogenic edema
2. sensitive to microstructural changes, detect abnormalities such as white matter disease prior to changes on conventional imaging.

Question 4

Functional imaging

Answer 4

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

Question 5

Single-Photon Emission Computed Tomography (SPECT)

Answer 5

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 due to less extensive technological requirements; radiotracers are stable enough that on-site chemist or cyclotron is NOT needed.

Question 6

Positron Emission Tomography (PET)

Answer 6

functional imaging

Radioisotope-based technology that examines GLUCOSE utilization.

Examines metabolic activity in brain cells engaged in cognitive tasks using radioisotope tracers (e.g., FDG or oxygen 15)

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; combined with other imaging for specific diagnostic questions like tumor characterization.
Con: Expense

Question 7

Functional Magnetic Resonance Imaging (fMRI)

Answer 7

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

Question 8

Electroencephalography (EEG)

Answer 8

Electrophysiological study

Monitors brain electrical activity (voltage fluctuations) along the scalp. Based on the sum of potentials.

Primary Purpose: Differentiate epileptic seizures from other types of events (e.g., nonepileptic seizures, fainting, or subcortical disorders).

Secondary Purposes: diagnosis of coma, determination of brain death, polysomnography, monitoring anesthesia

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

Question 9

Evoked Potentials (EPs)

Answer 9

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.

Question 10

Cerebral Arteriography (a.k.a. angiography)

Answer 10

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.

Question 11

Intracarotid Sodium Amobarbital Procedure (Wada testing)

Answer 11

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.

Question 12

Computed Tomographic Angiography (CTA)

Answer 12

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.

Question 13

Lumbar Puncture (spinal tap)

Answer 13

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

Question 14

Magnetic Resonance Angiogram (MRA)

Answer 14

Used to evaluate for stenosis, occlusions, and aneurysms.

Pros: Noninvasive compared to CTA.
Cons: poorer spatial resolution, less sensitivity to vessels with slower bloodflow, lengthier procedure time than CTA.

Question 15

fMRI vs PET

Answer 15

fMRI = measures oxygen changes in the brain

PET = measures glucose

Question 16

Imaging best for evaluating stroke

Answer 16

Diffusion weighted MRI

Question 17

How is the radioisotope used in neuroimaging technologies such as SPECT and PET?

Answer 17

absorbed by glial cells

Question 18

The EEG waveforms that predominate during sleep are

Answer 18

delta and theta

Question 19

Magnetic Resonance Spectroscopy (MRS)

Answer 19

MRI method used to localize and characterize brain-based biomarkers.

Can image endogenous biological markers: Creatinine, acid that assists with cell energy, and n-acetyl aspartate (NAA).

Can imagine Glutamate and choline – precusors to acetycholine.

MRS can detect brain-cell loss in degenerative diseases such as AD and MS.

Question 20

Lumbar Puncture (spinal tap)

Answer 20

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

Question 21

Types of Structural Imaging

Answer 21

Conventional x-ray
CT
MRI
Diffusion-weighted MRI
Perfusion-weighted MRI
Susceptibility-weighted Imaging (SWI)
Diffusion Tensor Imaging (DTI)
Magnetic Resonance Spectroscopy (MRS)
Magnetic Resonance Angiography (MRA)

Question 22

Types of Functional Imaging

Answer 22

Single-photon emission computed tomography (SPECT)
Positron Emission Tomography (PET)
Functional Magnetic Resonance Imaging (fMRI)

Question 23

Electrophysiological studies

Answer 23

Electroencephalography (EEG)
Evoked Potentials (EPs)
Electromyography (EMG) and Nerve Conduction Studies
Magnetoencephalography and Magnetic Source Imaging (MEG/MSI)

Question 24

Invasive Procedures

Answer 24

Cerebral Arteriography
Computed Tomographic Angiography (CTA)
Lumbar puncture

Question 25

What are the 4 wave forms in EEGs?

Answer 25

1. Alpha waves (i.e., 8–12 Hz waveforms) are observed in all age groups although more commonly in adults. Alpha amplitude manifests when the patient is relaxed with eyes closed and ablated by eye opening. They occur bilaterally in the posterior regions, being higher in amplitude on the dominant side. Frontal alpha consisting of alpha activity over anterior head regions may be related to drugs, anesthesia, or following arousal from sleep.
2. Beta waves (i.e., 12–30 Hz) are observed in all age groups. Beta is the dominant rhythm in patients who are alert, anxious, or have their eyes open. They are usually seen in symmetrical distribution and is most evident frontally. Beta activity is enhanced by sedating drugs such as benzodiazepines and barbiturates thought to be caused by a compensatory mechanism that allows for behavioral activation despite sedation.
3. Theta waves (i.e., 4–7 Hz) are observed in children and during sleep at any age. They may be transiently observed during normal wakefulness but are more prominent during drowsiness.
4. Delta waves (i.e., up to 4 Hz) are observed during sleep across all age groups and are normally the dominant rhythm in infants. They are observed more frontally in adults and posteriorly in children. Both theta and delta activity may occur in generalized distribution with diffuse disorders or metabolic encephalopathy.

Question 26

You are looking at medical records of a patient who was admitted to the emergency department due to acute head trauma. Which type of imaging will have been completed upon admission?

Answer 26

CT is the imaging modality of choice in acute trauma. Although MRI has better resolution, high field magnetization is unsafe for many trauma patients because of external stabilizers or cardiac leads. Single proton emission CT remains investigational in head trauma, as does DTI. In addition, traumatic axonal injury takes days or weeks to become detectable with DTI.

Question 27

The results of an electroencephalography (EEG) report that you receive describe waveforms that are associated with drowsiness, possibly associated with your patient’s use of sedatives. The waveform frequencies are most likely to be consistent with ____.

Answer 27

Beta waves

Beta is the dominant rhythm in patients who are alert, anxious, or have their eyes open. However, beta activity is also enhanced by sedating drugs such as benzodiazepines and barbiturates. This is thought to be caused by a compensatory mechanism that allows for behavioral activation despite sedation. Alpha amplitude manifests when the patient is relaxed with eyes closed, theta waves are prominent during drowsiness but can be observed during wakefulness, and delta waves are typically observed during sleep. The best answer is therefore “B.”

Question 28

Which cranial nerves project to extra ocular muscles involved in eye movement?

Answer 28

CN III, IV, and VI.

Question 29

Which cranial nerves have a gag reflex?

Answer 29

Cranial nerves IX (glossopharyngeal) and X (vagus)

Question 30

Dysdiadochokinesia

Answer 30

Dysdiadochokinesia refers to an impairment in alternating motor coordination. Dysmetria refers to unilateral movement. Cerebellar output is always ipsilateral, thus contralateral dysfunction is not a feasible response.

Question 31

What is the primary dependent variable in DTI?

Answer 31

Fractional anisotropy (FA).

Diffusion tensor imaging may be used to characterize DAI, but it is not a specific DTI index. The BOLD response is elicited in blood flow-based technologies such as fMRI. Cerebral metabolic rate of glucose metabolism( CMRGlu) is only measured with PET.

Question 32

What so EEG signals represent?

Answer 32

the summation of activity from thousands to millions of neurons

The EEG signal represents the summation of many relatively large areas of neurons. Although it is time-linked, it does not equate to single-neuron recording, nor is it specific to epileptiform activity.