Magnetic Resonance Spectroscopy (MRS) of the Brain Flashcards Preview

King's College London: Neuroimaging in Mental Health > Magnetic Resonance Spectroscopy (MRS) of the Brain > Flashcards

Flashcards in Magnetic Resonance Spectroscopy (MRS) of the Brain Deck (44)
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1
Q
What techniques use magnetic resonance (MR) phenomena?
A
- Nuclear Magnetic Resonance (NMR) Spectroscopy

- Magnetic Resonance Spectroscopy (MRS)

- Magnetic Resonance Imaging (MRI)
2
Q
What are the characteristics of Nuclear Magnetic Resonance (NMR) Spectroscopy?
A
- Chemical analysis

-Structural elucidation of compounds and macromolecules

-Chemical composition of solutions
3
Q
What is observed in an MRS?
A
Metabolites in a volume, or voxel.
4
Q
What is observed in an MRI?
A
Water protons whose magnetic properties change depending on its environment.
5
Q
What happens to a proton in a magnetic field?
A
Can either spin up or spin down.
6
Q
Which proton has lower energy?
A
Spin up protons.
7
Q
Which proton has higher energy?
A
Spin down protons.
8
Q
True or False: Protons resonate at different frequencies due to the presence of chemically bonded electrons.
A
True
9
Q
How does spin-spin coupling occur?
A
Arises from interactions between adjacent bonded magnetic nuclei.
10
Q
Spin-spin coupling is also called:
A
- Scalar coupling

- J-coupling
11
Q
How is scalar coupling (spin-spin coupling) measured?
A
- In hertz (is field independent)
12
Q
In spectroscopy, higher ________ _____ _________ result in greater __________ of the __________, thus making it easier to resolve them.
A
- magnetic field strengths

- dispersion

- resonances
13
Q
Proton Density:
When data is acquired when fully T-1 relaxed, the area under the peak is proportional to the:
a. Peak height
b. Number of protons
A
b. Number of protons.
14
Q
Reference Concentration:
_________ allows us to measure absolute metabolite concentration.
A
A reference
15
Q
When is a measurement of absolute concentration possible?
A
When a water spectrum is acquired; as long as we know the tissue/water concentration.
16
Q
True or false: Concentrations of metabolites are higher than concentrations of water and lipids/
A
False. Concentrations of waters and lipids are much higher than some of the metabolites.
17
Q
Metabolite signal intensity risks being ___________ by the relatively higher intensity of lipids and water.
a. swamped
b. increased
A
a. swamped
18
Q
Why is the water signal suppressed and voxels suppressed away from lipids?
A
To decrease the risk of metabolite signal intensity being swamped by the higher lipid and water concentrations.
19
Q
How is the voxel position selected?
A
Using a slice-selective RF pulse combined with magnetic field gradients.

*Similar to slice selection in MRI*
20
Q
Characteristics of SHORT echo times:
A
- Better signal to noise ratio

-TE = 35ms

- Complicated baseline due to macromolecules and lipids that make quantitation more difficult
21
Q
Characteristics of LONG echo time:
A
- More complicated quantitation because T2 relaxation needs to be accounted for

- TE = 136ms

- Simpler baseline: less complicated spectrum because short T2 molecules do not appear
22
Q
Main metabolites detected by proton MRS:
A
- Myo-inositol

- Choline

- Creatine

- Glutamate/Glutamine

- N-acetyl aspartate (NAA)

- Lactate and Lipids
23
Q
What has the most prominent peak in proton brain spectra?
A
- N-acetyl asparate (NAA)
24
Q
NAA is considered to be a marker of _________ _________.
A
neuronal integrity
25
Q
Where is N-acetyl asparate (NAA) synthesized?
A
In the mitochondria.
26
Q
What is the function of NAA?
A
The function of NAA is not yet known.
27
Q
What are the primary theories of the function of NAA?
A
- Possibly an organic osmolyte

- Possibly involved in myelin/lipid synthesis

- Precurser for neurotransmitter NAAG

- Storage form for asparate

- Linked to metabolic efficiency
28
Q
Are levels of creatine higher in grey matter or white matter?
A
Grey matter.
29
Q
What is creatine's role in the brain?
A
- Involved in energy metabolism

- Constant between individuals and brain regions
30
Q
Decreased levels in creatine result in ____ _____.
A
cell death.
31
Q
____ ______ can increase levels of creatine.
A
Head trauma
32
Q
Decreased levels of creatine could be caused by ________ __________.
A
creatine deficiency.
33
Q
Creatine deficiency could be a result of
A
- defects in synthesis or transport
34
Q
What is Myo-inositol?
A
A simple alcohol sugar.
35
Q
Myo-inositol is involved in _______ __________.
A
osmotic regulation.
36
Q
What is Myo-inositol used as?
A
An astrocyte or glial cell marker.
37
Q
When do Myo-inositol levels increase?
A
- Some dementia

- HIV infection

- Infancy
38
Q
Glutamate and glutamine is denoted glx when _____________________________.
A
the combined glu/gln is measured as a result of low field peaks overlapping.
39
Q
What is one of the most abundant compounds detected with proton MRS and is released by about 90% of excitatory neurons?
A
Glutamate
40
Q
____ is an __________ neurotransmitter whose peaks overlap the peaks from glutamate and glutamine.
A
- GABA

- inhibitory
41
Q
_______ is a doublet which means it has two peaks.
A
Lactate
42
Q
Lactate peaks are inverted/upside down at ____________ echo times.
A
intermediate
43
Q
_________ lactate levels are seen in hypoxia and ischaemia, mitochondria disorders, and some types of tumours.
A
Increased
44
Q
Lipids in the range of ___ to ___ ppm should not be seen in the normal brain.
A
0.9 to 1.5 ppm; are seen in some tumours