MRS in Multiple Sclerosis

Question 1

How is MRS done?

Answer 1

In conjuctions with standard imaging

Question 2

What does little box around image represent?

Answer 2

How you would plan a spectroscopy scan

It is a single voxel

Question 3

What occurs within the voxel?

Answer 3

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

Question 4

What does the spectrum contain?

Answer 4

Information and different metabolites which is often quantifiable

Question 5

What is metabolites?

Answer 5

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

Question 6

What does normal image acquire?

Answer 6

Signal from water

Question 7

Why should big voxels be used?

Answer 7

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

Question 8

What is big voxels useful for?

Answer 8

1. Studying big chunks of NAWM

2. In MS, when you have a large lesion

Question 9

When do you get partial volume effects?

Answer 9

Small lesions around the ventricles e.g. periventricular regions

Question 10

What is single voxel useful and not useful for?

Answer 10

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

Question 11

What does chemical shift in imaging acquire?

Answer 11

Whole slice of the brain and measure the metabolites in that

Question 12

In spectroscopy, where do you acquire spectrum from?

Answer 12

Each of the voxel above the lateral ventricles

Question 13

What is the grid [matrix in CSI?

Answer 13

Phase encoded

Question 14

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

Answer 14

Peaks that are observed in the spectrum or resonances

Question 15

What does each peak resonate at?

Answer 15

a specific frequency

The water will be at 4.7ppm

Question 16

What is water suppression technique?

Answer 16

Left with different metabolites at different frequencies

Question 17

Why do structures have different resonant frequency?

Answer 17

They all have a different chemical structure

Protons have a shielding effect from the main magnetic field

Question 18

What will the chemical structure have?

Answer 18

Different number of protons and other nuclei shielding

Question 19

What is linear regression used to find out?

Answer 19

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

Question 20

What does a T1 scan enable you to segment?

Answer 20

1. Grey matter
2. White matter
3. Correct for lesions

Question 21

What is the features of single voxel?

Answer 21

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

Question 22

What are the features of CSI?

Answer 22

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

Question 23

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

Answer 23

NAA

Question 24

What does tissue source of abnormaliities unknown mean?

Answer 24

Loss of specific localisation

Question 25

What does whole brain deficit exceeding 20% reflect?

Answer 25

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

Question 26

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

Answer 26

To avoid contimination from subcutaneous and bone marrow lipids

Question 27

What is whole-brain vs VOI?

Answer 27

- 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

Question 28

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

Answer 28

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

Question 29

How can you measure the spectra from?

Answer 29

Nuclei such as phosphorus, carbon, sodiun, chlorine

Question 30

What are the main metabolites observed in the spectra?

Answer 30

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

Question 31

What does lipids require?

Answer 31

Short echo time to acquire signal

Question 32

How do you lose signal from metabolites?

Answer 32

Long echo sequence

Question 33

What is involved in the lactate?

Answer 33

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

Question 34

What is the most prominent peak in healthy brain?

Answer 34

NAA | Marker for neurons

Question 35

What is used for GABA (neuroexcitatory neurotransmitter)

Answer 35

Special editing techniques | Get rid of NAA signal and see the GABA signal underneath

Question 36

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

Answer 36

1. Glutamate | 2. Glutamine

Question 37

What is GLX?

Answer 37

combination of glutamate and glutamine

Question 38

What is a marker for energy metabolism?

Answer 38

Phosphocreatine

Question 39

What are all the metabolites reported?

Answer 39

Relative to phosphocreatine because it is considered to be relatively stable

Question 40

What is a marker for cell membrane turnover?

Answer 40

Choline

Question 41

What is a marker for gliosis?

Answer 41

Myoinositol

Question 42

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

Answer 42

There is pulsatile flow through the cord

Question 43

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

Answer 43

Intervertrebral disc

Question 44

What is the significance of NAA?

Answer 44

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

Question 45

Where is there a greater reduction in NAA?

Answer 45

Progressive forms of MS e.g. RRMS

Question 46

What is the significance of reduced NAA?

Answer 46

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

Question 47

What is the significance of creatine?

Answer 47

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)

Question 48

In MS, where is there an increase in TCR?

Answer 48

NAWM

Question 49

What is the significance of choline?

Answer 49

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

Question 50

What is the significance of Glutamate/Glutamine?

Answer 50

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

Question 51

Increased Glutamate in NAWM and in lesions:

Answer 51

* 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)

Question 52

What is the significance of Myo-inositol?

Answer 52

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

Question 53

What is the quantification of metabolites?

Answer 53

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

Question 54

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

Answer 54

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

Question 55

In grey matter, what are the metabolites?

Answer 55

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

Question 56

What does more advanced form of MS show?

Answer 56

Greater metabolite changes

Question 57

What does not always correlate with disability in grey matter?

Answer 57

NAA and Glx

Question 58

In NAWM, what are the metabolites?

Answer 58

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

Question 59

What correlates with disability in RRMS?

Answer 59

NAA and Inositol

Question 60

What correlates with disability in SPMS?

Answer 60

tCho

Question 61

In spinal cord, what are the lesions?

Answer 61

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

Question 62

NAA

Answer 62

Neuroaxonal dysfunction or loss

Question 63

Glutamate-glutamine

Answer 63

Excitotoxic reaction-gliosis

Question 64

Creatine

Answer 64

Gliosis, metabolism

Question 65

Choline (inconsistent)

Answer 65

Membrane turnover - Inflammation, demyellination

Question 66

Myoinositol (Ins)

Answer 66

Glial proliferation, inflammation, microglial activation

Question 67

Lipids

Answer 67

Demyelination

Question 68

Lactate

Answer 68

Macrophage infiltrate in MS lesions

Question 69

What is lesion load better at differentiating?

Answer 69

SPMS and RRMS | A combination of these two would improve discrimination