Neuroimaging

Question 1

Identify factors to consider in imaging.

Answer 1

• Anatomy and Structure
• Symmetry (can compare the two sides in images of the brain)
• Incidentalomas (can pick up incidental findings which may not be of great significance but still worry the patient)
• Availability and cost (CT scan cheaper, more available)
• Practicality (in MRI need patient to be immobile for long period of time which can require giving anesthetics esp. for children, whereas in CT it’s quicker)
• Side effects (CT uses X-ray, magnetic strength in MRI rarely leads to side effects)

Question 2

Identify the main planes of the brain.

Answer 2

• Sagittal (along sagittal sinus)
• Transverse/Axial
• Coronal (ear to ear)

Question 3

What does CT stand for ?

Answer 3

Computerised Tomography

Question 4

What is the difference in amount of radiation between a CT with contrast and a chest X ray ? What is the clinical significance of this ?

Answer 4

CT with contrast has 200x more radiation than one CXR

This means that, for a patient who will likely require many rounds of imaging (e.g. patient with tumour), use MRI instead (less available so much less radiation, radiation from repeated CTs can induce tumour)

Question 5

Explain the basic technical points of a CT Scan.

Answer 5

• Caudal view (view image as looking from the patient’s feet)
• Diagonal image plane
• Generated by absorption

Question 6

Explain age effect in the context of neuroimaging.

Answer 6

As get older, there are changes in the brain which are not pathological, but rather reflex the increasing age:

-Atrophy (BUT make sure ventricles and sulci expand in proportionate way, otherwise worry about degenerative condition)

Question 7

What would expanded ventricles without large sulci suggest ?

Answer 7

Disproportionate atrophy, so not age-related but rather possible increased ICP.

Question 8

State how dense the main kinds of tissues are, correlating this with their color on a CT scan.

Answer 8

By decreasing density: 
Bone (white) 
Blood clot
Grey matter
White matter
CSF
Water (black) 
Fat
Air

Question 9

If we suspect a possible bone abnormality which cannot be picked up by regular brain CT, what can be done ?

Answer 9

Can adjust window of scanner to pick up specific bone abnormalities (in which case the brain stops being visible)

Question 10

What is the main problem with viewing structures in the posterior fossa on CT scans ? What is the solution to this ?

Answer 10

Bones can induce artifacts which can make it difficult to view structures in the posterior fossa. HENCE, use MRI scanning.

Question 11

Detail a system for interpretation of CT/MRI scans.

Answer 11

ABCs

A-Adequacy, Alignment, Artifact
B- Bones, Blood, Brain (compare two halves)
C- Cisterns, Ventricles (symmetrical? enlarged?)
S- Subcutaneous and Surfaces (lumps?)

Symmetry for everything

Question 12

What color is a cerebral bleed on a CT scan ?

Answer 12

Initially, white, then after times becomes darker

Question 13

Explain how a EDH can occur.

Answer 13

If trauma to side of the head, in region of middle meningeal artery, vulnerable areas, so hemorrhage can occur (usually in younger people), and victim can fall unconscious immediately.

Question 14

Explain how a chronic SDH can occur.

Answer 14

As get older, brains shrink and veins going to and from brain become more sensitive to trauma, so very easy if blow on head, to have rupture of vein,
which can cause to chronic SBH. Can last for weeks or months, and cause pressure effects (less likely to have acute deterioration than in acute SDH).

Question 15

Identify examples of uses of CT Angiography.

Answer 15

-To look for a subarachnoid hemorrhage

Question 16

Explain the basic technical points of an MRI Scan.

Answer 16

• Caudal view (view image as looking from the patient’s feet)
• Any plane
• CANNOT scan someone with metal in their body (e.g. pacemaker, cochlear implants, metal around eye/head) (should ask if exposed to metal)
• Generated by emission
• Main sequences used are weighted views (T1 sequence, and T2 sequence)

Question 17

Identify any differences in obvious age-related differences on MRI scans, cf CT scans.

Answer 17

-Atrophy present in both

-Areas of white matter abnormalities appear around ventricles and in the white matter (AKA UBOs). Physiologically, should have at most one of these per decadeof age. They are probably vascular.
If excessive amount, may be due to MS.

Question 18

Explain the physics of MRIs.

Answer 18

• Person goes into strong magnet
• Atomic nuclei reorient themselves along magnetic field
• Radiofrequency pulse flips nuclei from oriented position adn synchronizes the procession of their spin axis
• A receiver measures the time until the nuclei return to their original orientation (structural scans) or desynchronizes (functional scans)

Question 19

Distinguish between T1 and T2 sequences in MRI scanning.

Answer 19

• T1: spinal fluid black. Better for structural abnormalities
• T2: spinal fluid white. Better for areas for inflammation or ischemia

Question 20

Identify variants of MRI.

Answer 20

• Diffusion weighted
• ADC (apparent diffusion coefficient, uses DWI) maps/matrix
• FLAIR (fluid attenuated inversion recovery) (way of diminishing signal from fluid around brain)
• Angiography
• Functional (spectrography) (look at which parts of brain light up when doing particular tasks)

Question 21

What is the main difference between CT and MRI angiography ?

Answer 21

CT uses dye whereas MRI does not (relies entirely on movement of blood)

Question 22

Which MRI variants are used in strokes ?

Answer 22

DWI and ADC

Question 23

Explain how DWI and ADC may be used in strokes.

Answer 23

DWI = Diffusion weighted images (basically mix of T2 and
diffusion weighting).
ADC: Apparent Diffusion Coefficient, it’s pure diffusion of water.

Acutely, in stroke, 35 minutes after symptom onset, have high signal DWI and low signal ADC.
Over period of time, the two signals reverse:
-1-2 weeks, DWI stays high, ADC signal increases to normal.
-2 weeks +, DWI becomes lower, ADC becomes high and stays high).

This can help us to understand the timeframe of a stroke.

Question 24

Identify possible uses of MRI angiography.

Answer 24

• To look for an aneurysm
• To look for an arterioveinous malformation (can cause epilepsy and can bleed)
• To look for a thrombosis (e.g. in sagittal sinus or other sinus)

Question 25

What is MS?

Answer 25

Inflammation condition where immune system attacks insulation around nerves, brain, and spinal cord (timeline is relapses and remissions usually)

Question 26

Explain how injecting a contrast agent can help diagnosis of MS in MRI Scans.

Answer 26

Contrast agent shows areas where there has been a breakdown in BBB. There are little rings of BBB breakdown which occur right at the beginning of episodes of MS.

Question 27

Give an example of possible use of functional MRI for research.

Answer 27

Understanding which parts of the brain are involved in different areas of language, e.g. spelling, processing of speech, understanding of speech.

Question 28

Identify an allele which is a risk factor for dementia.

Answer 28

APOE4

Question 29

What does SPECT stand for ? What does it require ? What is its use ?

Answer 29

Single photon Emission Tomography
Requires radioisotope, gramma rays (common)
Picks up basal ganglia, picks up dopamine (hence can use it to distinguish between someone with normal basal ganglia,
and someone with Parkinson’s)

Question 30

What does PET stand for ? What does it require ? What is its use ?

Answer 30

Positron Emission Tomography
Requires cyclotron (less available) (for generation of particular types of isotopes and specific types of receivers/scanners)
Some used for detection of cancer. Usually for research, not diagnosis (not common for diagnosis).