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OD2 S2 > wk4: ND - Medical Imaging and VEPs > Flashcards

wk4: ND - Medical Imaging and VEPs Flashcards

1
Q

Are X-rays mutagenic or non-mutagenic?

A

Mutagenic

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2
Q

Define mutagenic

A

a mutagen is a physical or chemical agent that changes the genetic material, usually DNA, of an organism and thus increases the frequency of mutations above the natural background level.

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3
Q

What kind of exposure does tissue and bone give in an X-ray?

A

Tissue: high exposure
Bone: little to no exposure

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4
Q

What kind of exposure does dense tissue such as muscle give in an X-ray

A

Little to moderate exposure

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5
Q

List 5 applications of X-rays

A

Visualise orbital bones/sinuses:
- After injury or trauma
- Changes to structure
- FBs
- Brain stem-spine/CNS
- Screening tool for metal foreign bodies prior to orbital MRI

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6
Q

What is the first 3D imaging technique?

A

CT scans

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7
Q

Which is cheaper: X-rays or CT scans?

A

X-rays

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8
Q

How are CT scans carried out and with what kind of beam?

A

X-rays in a fan beam, rotating around the patient

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9
Q

Like X-rays, what are CT scans best at detecting?

A

Bony structures (however they can also image soft tissues too)

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10
Q

What kind of resolution is given by an MRI scan and what kind of tissue is it good for?

A

High resolution. Great for non-calcified tissue

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11
Q

List the basic principles behind how MRI works (7)

A
  1. Body is made up largely of water
  2. Hydrogen nuclei (protons) become aligned in magnetic field
  3. MRI applies a very strong magnet (typically 1.5 or 3T) to align the proton “spins”
  4. Also apply a radio frequency (RF) current that varies the magnetic field
  5. Protons absorb energy from this variable current and flip their “spins”
  6. When turned off,the protons return to normal state but this process varies depending on tissue density and results in the emission of RF energy
  7. The emitted RF energy is used to create 2D images
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12
Q

In brief terms, describe how MRI works. How can you see tissue density?

A

Protons aligned in a magnetic field absorb some energy and misallign slightly. When you turn off the magnetic field: the protons re-allign. The time taken to reallign is based on the RF energy, which is what is collected. Because there is differences in RF energy, you can see tissue density

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13
Q

Define the two components of a structural MRI. Explain what they describe. Do they vary between tissues?

A

T1 - longitudinal relaxation time
T2 - transverse relaxation time
Both describe different aspects of how the protons return to equilibrium after the applied radio frequency pulse.
T1 and T2 signals vary between tissues resulting in different image qualities

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14
Q

Define Repetition Time (TR)

A

amount of time between successive pulse sequences applied to the same slice

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15
Q

Define Time to Echo (TE)

A

the time between the delivery of the RF pulse and the receipt of the echo signal

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16
Q

What structures have the following colours on a T1 weighted MRI image:
Black (3)
Dark (3)
Grey (1)
Bright/White (2)

A

Black: air, bone, calcium
Dark: CSF, oedema, most lesions
Grey: White and grey matter
White: Fat, blood

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17
Q

What structures have the following colours on a T2 weighted MRI image:
Black (3)
Dark (1)
Bright/White (4)

A

Black: air, calcium, bone
Dark: white matter, grey matter
Bright: CSF, blood, oedema, most lesions

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18
Q

What does FLAIR stand for and what does it consist of? (2)

A

Fluid attentuation inverted recovery. Consists of a long TE (echo time) and a long TR (repetition time)

Woo

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19
Q

What does FLAIR result in? (2)

A

Abnormalities remain bright but CSF is attenuated

Also results in a 16x world champion. “To be the man, woo, you gotta beat the man” *Strips off pants

20
Q

What does Diffusion weighted imaging measure? What is it good for?

A

Is a form of MRI that measures the movement of water molecules within a voxel of tissue. Very good for visualising stroke

21
Q

Describe the basic principles of 1H Magnetic Resonance Spectroscopy (4)

A

Each proton can be visualised at a specific chemical shift (peak position along x axis)
This depends on its chemical environment
It is dictated by neighbouring protons within the molecule
Metabolites can be characterised by their unique set of 1H chemical shifts

22
Q

What does Magnetic Resonance Spectroscopy allow for? What is the benefit of this?

A

Allows the chemical composition of an area of brain to be determined. This helps develop cancer medication as different tumours have different metabolic composition

23
Q

What is a contrast medium? Provide examples for contrast media in CT scans (2) and MRI (1)

A

substance with different attenuation properties to tissue. E.g. CT scan: iodine, barium sulphate. MRI: gadolinium

24
Q

Can water be used as a contrast medium?

A

yes. Even something as simple as water can be used in contrast medium for something like stomach imaging for example

25
Q

What is digital subtraction angiography (DSA)?

A

image of region taken with medium is subtracted from image taken before medium, leaving medium defined (blood) outcome

26
Q

What is DSA with CT good for? What is DSA with MRI good for? Waht is war good for?

A

DSA with CT: good for vessels
DSA with MRI: good for vascular rich structures
War: good for absolutely nothing

27
Q

Describe how PET scans work. What are they good for imaging?

A

Inject small amount of liquid radioactive substance (most common FDG)
Gives off energy in form of gamma rays
Shows how/where sugar is being used by the body
- Tumours require substantial sugar to grow, so commonly used for cancer imaging

28
Q

Why use Electrodiagnostic methods? (2 clinical reasons, 1 scientific reason)

A

Clinically:
- Diagnosis/prognosis for disease
- Determination of visual function in uncooperative patients
Scientific:
- Non-invasively determine properties/behaviour of retinal cells and visual pathways

29
Q

How do we most commonly refer to a brain wave evoked by visual stimulation? Can we measure this with Electroencephalophagram?

A

VEP: Visual evoked potential. Yes

30
Q

How is VEP carried out and in reference to what?

A

Place 2 electrodes on the back of the head in reference to bony landmarks

31
Q

What are the two basic grid patterns when recording VEP?

A

Ten-twenty grid: Either 10% or 20% of total distance – accounts for different head sizes
Queen’s square (QS) grid: 5 cm steps along Z- or C-lines

32
Q

What type of stimuli are used in VEP measurement? (2) Should the stimulus vary?

A

Require a varying stimulus because it is the change that evokes a response
Can be a:
Flash VEP or
Pattern VEP

33
Q

What happens to macula responses in VEP imaging? Why?

A

They are amplified, because a lot of our brain is dedicated to the macula

34
Q

What does PVEP P100 refer to?

A

refers to 100ms after the Pattern VEP stimulus onset. This is where we would normally expect our response or “peak”

35
Q

When is PVEP P100 not 100ms?

A

A time delay in the response to the stimulus can occur when the patient has a demyelinating condition such as optic neuritis. In this instance, it would be slightly more than 100ms

36
Q

How can the amplitude of the VEP response vary? (2)

A

Variability in cortical folding/dipole directions
Amount of conductance of skin electrodes

37
Q

What is VEP serial to?

A

ERG

38
Q

In a Pattern Electroretinogram (PERG), what does P50 and N95 refer to? Name a disease that can affect each of these components (2)

A

P50: positive peak 50ms after onset, associated with inner retina (maculopathy)
N95: negative peak 95ms after onset, associated with ganglion cell (optic neuropath)

39
Q

Assume a patient has a disease affecting their macula like macula dystrophy. How will their electrodiagnostic imaging results likely be affected? (3)

A

Normal full-field ERG
Abnormal PERG P50 (N95:P50 ratio not reduced)
Delayed pattern VEP

40
Q

Assume a patient has a disease affecting RGCs such as dominant optic atrophy. How will their electrodiagnostic imaging results likely be affected? (3)

A

Normal full-field ERG
Abnormal PERG N95 (N95:P50 ratio reduced)
Delayed, abnormal pattern VEP

41
Q

Consider a patient with unexplained vision loss with: abnormal pattern VEP, normal pattern ERG. What condition might they have? (1)

A

Optic Nerve dysfunction

42
Q

Consider a patient with unexplained vision loss, abnormal PVEP, abnormal PERG and Normal P50 (abnormal N95). What is a possible condition they may have?

A

Optic nerve dysfunction

43
Q

Consider a patient with unexplained vision loss, abnormal PVEP, abnormal PERG, abnormal P50 and normal ERG. What is a possible condition they may have?

A

Macular dysfunction

44
Q

Consider a patient with unexplained vision loss, abnormal PVEP, abnormal PERG, abnormal P50, abnormal ERG. What is a possible condition they may have?

A

Retinal dysfunction

45
Q

What type of resolution do X-rays have? Coarse or Fine?

A

X-ray radiation gives coarse resolution

OD2 S2 (63 decks)

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