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C2 Modules CLINICAL > MRS in Multiple Sclerosis > Flashcards

MRS in Multiple Sclerosis Flashcards

1
Q

How is MRS done?

A

In conjuctions with standard imaging

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2
Q

What does little box around image represent?

A

How you would plan a spectroscopy scan

It is a single voxel

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3
Q

What occurs within the voxel?

A

Define the area and that is where you will acquire your spectum from?

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4
Q

What does the spectrum contain?

A

Information and different metabolites which is often quantifiable

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5
Q

What is metabolites?

A

A thousand of times less concentrated than the water in the brain

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6
Q

What does normal image acquire?

A

Signal from water

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7
Q

Why should big voxels be used?

A

Get enough signal to be able to get good signal to noise and get good resolution

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8
Q

What is big voxels useful for?

A
  1. Studying big chunks of NAWM

2. In MS, when you have a large lesion

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9
Q

When do you get partial volume effects?

A

Small lesions around the ventricles e.g. periventricular regions

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10
Q

What is single voxel useful and not useful for?

A
  1. Useful for:
    - NAWM
    - Large lesions
  2. Not useful for:
    - Small lesions
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11
Q

What does chemical shift in imaging acquire?

A

Whole slice of the brain and measure the metabolites in that

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12
Q

In spectroscopy, where do you acquire spectrum from?

A

Each of the voxel above the lateral ventricles

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13
Q

What is the grid [matrix in CSI?

A

Phase encoded

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14
Q

What are specific to certain metabolites and they depend on the chemical environment of the protons in the compound?

A

Peaks that are observed in the spectrum or resonances

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15
Q

What does each peak resonate at?

A

a specific frequency

The water will be at 4.7ppm

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16
Q

What is water suppression technique?

A

Left with different metabolites at different frequencies

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17
Q

Why do structures have different resonant frequency?

A

They all have a different chemical structure

Protons have a shielding effect from the main magnetic field

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18
Q

What will the chemical structure have?

A

Different number of protons and other nuclei shielding

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19
Q

What is linear regression used to find out?

A

What the concentration is e.g. in a WM lesion

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20
Q

What does a T1 scan enable you to segment?

A
  1. Grey matter
  2. White matter
  3. Correct for lesions
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21
Q

What is the features of single voxel?

A
  1. Scan time: short
  2. Efficiency: low
  3. Processing: Straight forward
  4. Spatial information: minimal
  5. Voxel shape: good
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22
Q

What are the features of CSI?

A
  1. Scan time: long
  2. Efficiency: high
  3. Processing: More complex
  4. Spatial information: high
  5. Voxel shape: poorer
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23
Q

What is the most prominent resonance we see in the spectrum?

A

NAA

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24
Q

What does tissue source of abnormaliities unknown mean?

A

Loss of specific localisation

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25
Q

What does whole brain deficit exceeding 20% reflect?

A 
GM involvement 
(as WM:GM volume=40:60; NAA in WM is 2/3 of NAA in GM)
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26
Q

What must be placed away from the skull, thereby missing most of the cortex?

A

To avoid contimination from subcutaneous and bone marrow lipids

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27
Q

What is whole-brain vs VOI?

A
  • It must be visually positioned onto MR imaging-visible pathology or NAWM
  • It encounters misregistration errors in longitudinal studies
  • VOI may require a long acquisition time to obtain sufficient signal-intensity quality
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28
Q

What does 1mm difference mean in whole-brain vs VOI mean?

A

The result is 70% from the common space in both those measurements

29
Q

How can you measure the spectra from?

A

Nuclei such as phosphorus, carbon, sodiun, chlorine

30
Q

What are the main metabolites observed in the spectra?

A
  1. Lipids
  2. Lactate
  3. NAA
  4. Glutamate/GABA
  5. Creatube/phosphocreatine
  6. Choline compounds
  7. Myo-inositol
31
Q

What does lipids require?

A

Short echo time to acquire signal

32
Q

How do you lose signal from metabolites?

A

Long echo sequence

33
Q

What is involved in the lactate?

A

J-Coupling

Acquire the lactate doublet and it is in 144-288ms

34
Q

What is the most prominent peak in healthy brain?

A

NAA

Marker for neurons

35
Q

What is used for GABA (neuroexcitatory neurotransmitter)

A

Special editing techniques

Get rid of NAA signal and see the GABA signal underneath

36
Q

What is quite difficult to resolve at clinical field of 3T?

A
  1. Glutamate

2. Glutamine

37
Q

What is GLX?

A

combination of glutamate and glutamine

38
Q

What is a marker for energy metabolism?

A

Phosphocreatine

39
Q

What are all the metabolites reported?

A

Relative to phosphocreatine because it is considered to be relatively stable

40
Q

What is a marker for cell membrane turnover?

41
Q

What is a marker for gliosis?

A

Myoinositol

42
Q

Why is there a lot more challenge involved in spinal cord spectroscopy?

A

There is pulsatile flow through the cord

43
Q

What causes a lot of inhomogeneity and is the enemy of spectroscopy?

A

Intervertrebral disc

44
Q

What is the significance of NAA?

A
  1. Synthesis in neuronal mitochondria
  2. Ratio grey/white: 1.2
  3. Marker of neuronal loss/dysfunction
  4. Oligodendrocytes precursors
  5. Neuron-glia signalling
45
Q

Where is there a greater reduction in NAA?

A

Progressive forms of MS e.g. RRMS

46
Q

What is the significance of reduced NAA?

A
  1. Neuronal/axonal loss
  2. Neuronal metabolic dysfunction
  3. Spectroscopic markers have been backed up by histology from same samples
47
Q

What is the significance of creatine?

A
  1. Marker of ‘‘intact brain energy metabolism’’
  2. Ratio grey/white: 1.7
  3. Systemic impact: kidney diseases, mestastasis, diet, birth
  4. Used as internal reference (ratios)
48
Q

In MS, where is there an increase in TCR?

49
Q

What is the significance of choline?

A
  1. choline peak measures total levels of mobile choline compounds
    - free choline (<5%), acetylcholine, glycerophosphorylcholine, phosphocholine
  2. Membrane phosphatidylcholine is not visible on MRS at 3T
  3. Ratio grey/white 0.9
50
Q

What is the significance of Glutamate/Glutamine?

A
  1. Indistinguishable without editing
  2. Ratio grey/white: 2.4
  3. Gln: astrocyte marker
  4. Glu: coupled to NAA
51
Q

Increased Glutamate in NAWM and in lesions:

A
  • This suggested inflammatory cells and astrocytosis
  • Longitudinal study showed baseline Glutamate predicted decreased NAA at 5yr follow up
  • Glu/NAA predicted brain volume decrease and clinical scores (MSFC and PASAT)
52
Q

What is the significance of Myo-inositol?

A
  1. Astrocyte marker/ osmolyte
  2. Ratio grey/white: 1.6
  3. Decrease in: hepatic encephalopathy
  4. Increase in: Adenoleukodystrophy (ALD), Krabbe’s leukodystrophy
53
Q

What is the quantification of metabolites?

A
  1. Ratios
  2. Absolute measurements
  3. Measurements underneath the peak
  4. Take patients out and replace with a phantom of no concentration scan all under the same condition
54
Q

In MS, what are the WM lesions (metabolites)?

A
  1. Decrease in NAA
  2. Increase in Choline
  3. Increase in Inositol
  4. Increase in lactate
  5. Increase and decrease in Creatine = not reliable
55
Q

In grey matter, what are the metabolites?

A
  1. NAA is reduced in cortex (inconsistent) and thalamus (consistent)
  2. Glutamate-glutamine is reduced in cortex (inconsistent)
56
Q

What does more advanced form of MS show?

A

Greater metabolite changes

57
Q

What does not always correlate with disability in grey matter?

A

NAA and Glx

58
Q

In NAWM, what are the metabolites?

A
  1. NAA is reduced in NAWM
  2. Inositol is elevated
  3. Creatine and choline are elevated
59
Q

What correlates with disability in RRMS?

A

NAA and Inositol

60
Q

What correlates with disability in SPMS?

61
Q

In spinal cord, what are the lesions?

A
  1. Technically difficult
  2. NAA is reduced in NAWM and lesions
  3. NAA and Insotiol correlate with disability
  4. Diffuse vs focal lesions
    - diffuse had increased Cr, decreased NAA
  5. NAA/Cr correlated to clinical progression
  6. Lower NAA and Glx in PPMS relative to controls
62
Q

NAA

A

Neuroaxonal dysfunction or loss

63
Q

Glutamate-glutamine

A

Excitotoxic reaction-gliosis

64
Q

Creatine

A

Gliosis, metabolism

65
Q

Choline (inconsistent)

A

Membrane turnover - Inflammation, demyellination

66
Q

Myoinositol (Ins)

A

Glial proliferation, inflammation, microglial activation

67
Q

Lipids

A

Demyelination

68
Q

Lactate

A

Macrophage infiltrate in MS lesions

69
Q

What is lesion load better at differentiating?

A

SPMS and RRMS

A combination of these two would improve discrimination

C2 Modules CLINICAL (26 decks)

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