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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
What does whole brain deficit exceeding 20% reflect?
``` GM involvement (as WM:GM volume=40:60; NAA in WM is 2/3 of NAA in GM) ```
26
What must be placed away from the skull, thereby missing most of the cortex?
To avoid contimination from subcutaneous and bone marrow lipids
27
What is whole-brain vs VOI?
- 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
28
What does 1mm difference mean in whole-brain vs VOI mean?
The result is 70% from the common space in both those measurements
29
How can you measure the spectra from?
Nuclei such as phosphorus, carbon, sodiun, chlorine
30
What are the main metabolites observed in the spectra?
1. Lipids 2. Lactate 3. NAA 4. Glutamate/GABA 5. Creatube/phosphocreatine 6. Choline compounds 7. Myo-inositol
31
What does lipids require?
Short echo time to acquire signal
32
How do you lose signal from metabolites?
Long echo sequence
33
What is involved in the lactate?
J-Coupling | Acquire the lactate doublet and it is in 144-288ms
34
What is the most prominent peak in healthy brain?
NAA | Marker for neurons
35
What is used for GABA (neuroexcitatory neurotransmitter)
Special editing techniques | Get rid of NAA signal and see the GABA signal underneath
36
What is quite difficult to resolve at clinical field of 3T?
1. Glutamate | 2. Glutamine
37
What is GLX?
combination of glutamate and glutamine
38
What is a marker for energy metabolism?
Phosphocreatine
39
What are all the metabolites reported?
Relative to phosphocreatine because it is considered to be relatively stable
40
What is a marker for cell membrane turnover?
Choline
41
What is a marker for gliosis?
Myoinositol
42
Why is there a lot more challenge involved in spinal cord spectroscopy?
There is pulsatile flow through the cord
43
What causes a lot of inhomogeneity and is the enemy of spectroscopy?
Intervertrebral disc
44
What is the significance of NAA?
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
Where is there a greater reduction in NAA?
Progressive forms of MS e.g. RRMS
46
What is the significance of reduced NAA?
1. Neuronal/axonal loss 2. Neuronal metabolic dysfunction 3. Spectroscopic markers have been backed up by histology from same samples
47
What is the significance of creatine?
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
In MS, where is there an increase in TCR?
NAWM
49
What is the significance of choline?
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
What is the significance of Glutamate/Glutamine?
1. Indistinguishable without editing 2. Ratio grey/white: 2.4 3. Gln: astrocyte marker 4. Glu: coupled to NAA
51
Increased Glutamate in NAWM and in lesions:
* 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
What is the significance of Myo-inositol?
1. Astrocyte marker/ osmolyte 2. Ratio grey/white: 1.6 3. Decrease in: hepatic encephalopathy 4. Increase in: Adenoleukodystrophy (ALD), Krabbe's leukodystrophy
53
What is the quantification of metabolites?
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
In MS, what are the WM lesions (metabolites)?
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
In grey matter, what are the metabolites?
1. NAA is reduced in cortex (inconsistent) and thalamus (consistent) 2. Glutamate-glutamine is reduced in cortex (inconsistent)
56
What does more advanced form of MS show?
Greater metabolite changes
57
What does not always correlate with disability in grey matter?
NAA and Glx
58
In NAWM, what are the metabolites?
1. NAA is reduced in NAWM 2. Inositol is elevated 3. Creatine and choline are elevated
59
What correlates with disability in RRMS?
NAA and Inositol
60
What correlates with disability in SPMS?
tCho
61
In spinal cord, what are the lesions?
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
NAA
Neuroaxonal dysfunction or loss
63
Glutamate-glutamine
Excitotoxic reaction-gliosis
64
Creatine
Gliosis, metabolism
65
Choline (inconsistent)
Membrane turnover - Inflammation, demyellination
66
Myoinositol (Ins)
Glial proliferation, inflammation, microglial activation
67
Lipids
Demyelination
68
Lactate
Macrophage infiltrate in MS lesions
69
What is lesion load better at differentiating?
SPMS and RRMS | A combination of these two would improve discrimination

C2 Modules CLINICAL (26 decks)

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