fMRI

Question 1

What is diffusion weighted MRI?

Answer 1

Evaluates the movement of water molecules
3D representation of diffusion
Calculates how freely hydrogen atoms move within a structure
Increases the sensitivity of MRI
Improved signal to noise ratio
Reduced image acquisition time
Limited spatial resolution
Cannot be used in isolation

Question 2

What are the different types of diffusion?

Answer 2

Unrestricted - CSF; rapid diffusion of water molecules
Preferential - structure (cell bodies) restricts hydrogen atom movement; movement typically in one direction
Restricted - abnormalities represent alterations in the random movement oof water molecules in tissue; abnormalities can occur in many neurological conditions

Question 3

Does function testing need to be combined with other radiology tests and clinical information to support diagnosis?

Answer 3

Yes
Stroke - high signal due to swelling of cells and changes in intra and extra cellular space
Tumor - low signal due to increased cellularity
Cyst - high signal due to fluid with free movement within the cyst
Infection or inflammation - signal varies
Neurodegenerative disorders - high signal due to decrease in barrier to water molecule movement

Question 4

Is fMRI more sensitive to stroke than FLAIR?

Answer 4

Yes
Reveals alterations in water movement
Earlier identification (within minutes)
More sensitive for anterior circulation than posterior circulation

Question 5

Does MRI with DWI help refine the diagnosis of arachnoid cysts?

Answer 5

Yes
Important to differentiate between arachnoid and epidermal cysts
The 2 masses may have similar characteristics on T1-weighted and T2-weighted images, and neither shows enhancement with gadolinium
However, arachnoid cysts follow CSF signals on all sequences—in particular, on the FLAIR sequence
FLAIR imaging demonstrates tissue contrast similar to that of T2-weighted images, but FLAIR shows no signal arising from the CSF
Therefore, FLAIR demonstrates a suppressed or low signal in arachnoid cysts that contain CSF
In epidermoid cysts, that signal is typically higher
Arachnoid cysts can enlarge over time
Mass effect must be carefully assessed
Immediate intervention is needed even for a subtle mass effect due to brain herniation

Question 6

What is diffusion tensor imaging (DTI)?

Answer 6

Technical improvement of DWI
DTI detects how water travels along the white matter tracts in the brain
A tool for assessing white matter tracts
Low acquisition time
Less artifact
Color coded based on the primary direction of water motion (red - left to right, green - anterior to posterior, blue - superior to inferior)

Question 7

What are the white matter tracts?

Answer 7

Fibers that connect different parts of the brain and must be protected during surgery
Defined orientation of tracts and underlying structure

Question 8

Can DWI give us information in the direction of molecular movement?

Answer 8

No

Question 9

Can lesions displace the primary sensorimotor cortices and the white matter associated with the area?

Answer 9

Yes

Question 10

What is functional MRI?

Answer 10

Cerebral blood flow and neuronal activation are couples
Detects blood oxygen level changes in the brain
Pinpoint areas of the brain handling critical function

Question 11

How does fMRI work?

Answer 11

Neural activity results in increased blood flow to the area of activation
Hemoglobin is the oxygen delivery system via capillary red blood cells
Comparing the magnetism of oxygenated blood to deoxygenated blood can pinpoint areas of neural activation in the brain
Neuronal activity increase demands an increase in oxygen carried by the blood; therefore, the response is an increase in blood flow to the area
Diamagnetic electrons or paired electrons are magnetized and repel to 180 degrees of the magnetic field
Richly oxygenated blood is diamagnetic
Paramagnetic electrons or unpaired electrons are not magnetized and attract or align in response to the magnetic field
Poorly oxygenated blood is paramagnetic

Question 12

Does oxygen rich and oxygen poor blood have different magnetic resonance?

Answer 12

Yes
Hemoglobin is diamagnetic when oxygenated (repels 180 degrees from the magnetic field) and paramagnetic when deoxygenated (aligns or attracts to the magnetic field)

Question 13

What is the basis of the BOLD effect?

Answer 13

Blood Oxygen Level Dependent imaging measures human brain activity
Measures the magnetic resonance of hemoglobin to locate neural activity in the brain

Question 14

What affects the BOLD signal?

Answer 14

Blood flow - neural activity increases demand for oxygen
Blood volume - increased blood flow through vasodilation
Oxygen metabolism

Question 15

What is the fMRI image?

Answer 15

Computer processes the signals into a 3D image
Brain activity is “mapped” in voxels
Each voxel represents thousands of neurons
Voxels are scored based on the correlation of activity (the amount of oxygenated blood in that area)
Comparison of oxygenation and de-oxygenation hemoglobin produces a highlighted image
Color highlights the active areas
An activation map is created

Question 16

What is brain mapping?

Answer 16

Specific tasks are requested of the patient to increase the oxygen rich blood flow to certain areas
Patient alternates between a specific task and a resting state
Data is analyzed, looking for common patterns
A brain map or activity map is created that highlights the areas of greatest oxygenated blood

Question 17

What are the fMRI advantages?

Answer 17

Convenient
Non-invasive
Non-ionizing radiation (multiple studies on the same patient)
Good spatial and temporal resolution
30-45 minutes

Question 18

What are the fMRI disadvantages?

Answer 18

Scanner is very noisy, may contaminate the image (may activate hearing areas of the brain)
Need custom non-magnetic headphones
Movement artifact
Not a direct measure of neural activity
Irregular heartbeat may affect images

Question 19

What are the potential uses of fMRI?

Answer 19

Localization of functional systems
Comparison of clinical pathology to normal groups
Study how a tumor, stroke or trauma like concussion alters brain function
Monitoring of disease over time
Pre and post surgical function of a specific area
Planning of radiotherapy or other invasive surgical procedures

Question 20

Does fMRI add function to high resolution structural MRI?

Answer 20

Yes
Functional tests are often combined with tests of structure
Other tests that demonstrate function: PET and SPECT
Space occupying lesions may displace anatomical landmarks of primary sensory and motor areas
fMRI can play a major role in pre-surgical brain mapping for strategic removal of tumors in critical brain areas
fMRI is successful in isolating critical language related brain regions (Broca’s and Wernicke’s)

Question 21

Are PET and SPECT considered nuclear medicine?

Answer 21

Yes, uses a radioactive tracer and contrast agent
fMRI is the least invasive because of non-ionizing radiation

Question 22

Does fMRI measure small changes in blood flow as a person performs tasks?

Answer 22

Yes
Studies of plasticity help surgeons understand how a tumor, stroke, or trauma alters the brains function

Question 23

Can fMRI play a major role in pre-surgical brain mapping?

Answer 23

Yes, for strategic removal of tumors in critical brain areas
Language areas, motor areas, and sensory areas can be mapped prior to surgery
Successful in isolating critical language related brain regions

Question 24

Does increased neuronal activity lead to increased demand for oxygen?

Answer 24

Yes

Question 25

What is plasticity?

Answer 25

Cerebral reorganization The capacity of remaining areas to assume functions that are normally assumed by the damaged areas Can be viewed with fMRI and DTI

Question 26

Does fMRI help to identify the least invasive pathway for removal?

Answer 26

Yes, done by localizing motor and sensory pathways Tasks selected based on the location of the tumor and the areas surrounding the surgical location Maximize extent of resection, which is positively related with lower rates of recurrence and long-term tumor control

Question 27

What is DTI?

Answer 27

Shows displacement of the corona radiata (ascending and descending axons that connect the brainstem to the cerebral cortex), extending the direction of activation of white matter tracts suggesting cortical redistribution, consistent with fMRI

Question 28

What are some of the things that can affect fMRI results?

Answer 28

Proper task selection (stimulating the areas you want) Correct statistical analysis and threshold setting (make sure enough blood is flowing to the area) Appropriate patient cooperation

Question 29

What are biomarkers for disease?

Answer 29

Characteristics of a disease or disorder fMRI studies have focused on cerebral functional connectivity to better understand the mechanisms of the brain and how neural connections are affected by disease fMRI research finds that alterations in both auditory and non-auditory systems play a role in tinnitus Research is being done to identify biomarkers for certain disorders

Question 30

How should tinnitus be evaluated with fMRI? What is typically seen?

Answer 30

Resting state fMRI, no tasks Structural and functional anomalies of the central auditory system: Neural networks alterations (decreased cerebral blood flow in auditory and prefrontal cortex, white matter tracts, corpus collosum and cingulate gyrus) Auditory system, limbic system, Attention system and default mode network (memory, emotion, attention)

Question 31

Is there diagnostic value with fMRI for tinnitus?

Answer 31

Yes Developed a convolutional neural network architecture model for diagnosis of tinnitus AI model for the automatic classification of tinnitus using fMRI Clinical application of diagnostic biomarkers Anterior cingulate cortex, thalamus, and temporal lobe The frontal part of the cingulate that surrounds the front part of the corpus collosum Involved in higher-level function like emotion, memory and attention

Question 32

What damage does concussion cause?

Answer 32

Damage to neurons Inflammation Change in metabolic state Tearing and shearing of the neural axons Compromises brain function Interrupts communication between neurons

Question 33

Is there a gold standard for concussion diagnostic testing?

Answer 33

No Typically invisible on routine diagnostic imaging Symptoms are subjective and variable

Question 34

What are some concussion symptoms?

Answer 34

Difficulty concentrating Irritability Mood changes

Question 35

Could fMRI play a critical role in advancing concussion diagnosis?

Answer 35

Supplement clinical tests with functional imaging Neuropathology is not easily identified on routine CT and MRI Neuroimaging techniques are mainly used in research and are expensive fMRI could help determine single concussion versus multiple traumas

Question 36

What is functional neurocognitive imaging (fNCI)?

Answer 36

An objective measure allowing treatment to target specific cognitive areas and accelerate recovery fNCI displays brain function after trauma If the area is not receiving enough blood (oxygen), difficulty completing the task may result If too much blood is sent to the area, the result may be fatigue and headache. Results from concussed subjects are compared to a normative database

Question 37

Does fNCI have high accuracy in diagnosing concussion?

Answer 37

Yes 98% accurate in diagnosing concussion Unique test battery called Severity Index Score Biomarkers that are distinctly different than other neurological disorders 5 reliable markers for concussion using the fCNI protocol More research needed to generalize to all treatment centers