Magnetic Resonance Spectroscopy (MRS) of the Brain Flashcards
What techniques use magnetic resonance (MR) phenomena?
- Nuclear Magnetic Resonance (NMR) Spectroscopy
- Magnetic Resonance Spectroscopy (MRS)
- Magnetic Resonance Imaging (MRI)
What are the characteristics of Nuclear Magnetic Resonance (NMR) Spectroscopy?
- Chemical analysis
- Structural elucidation of compounds and macromolecules
- Chemical composition of solutions
What is observed in an MRS?
Metabolites in a volume, or voxel.
What is observed in an MRI?
Water protons whose magnetic properties change depending on its environment.
What happens to a proton in a magnetic field?
Can either spin up or spin down.
Which proton has lower energy?
Spin up protons.
Which proton has higher energy?
Spin down protons.
True or False: Protons resonate at different frequencies due to the presence of chemically bonded electrons.
True
How does spin-spin coupling occur?
Arises from interactions between adjacent bonded magnetic nuclei.
Spin-spin coupling is also called:
- Scalar coupling
- J-coupling
How is scalar coupling (spin-spin coupling) measured?
- In hertz (is field independent)
In spectroscopy, higher ________ _____ _________ result in greater __________ of the __________, thus making it easier to resolve them.
- magnetic field strengths
- dispersion
- resonances
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
b. Number of protons.
Reference Concentration:
_________ allows us to measure absolute metabolite concentration.
A reference
When is a measurement of absolute concentration possible?
When a water spectrum is acquired; as long as we know the tissue/water concentration.
True or false: Concentrations of metabolites are higher than concentrations of water and lipids/
False. Concentrations of waters and lipids are much higher than some of the metabolites.
Metabolite signal intensity risks being ___________ by the relatively higher intensity of lipids and water.
a. swamped
b. increased
a. swamped
Why is the water signal suppressed and voxels suppressed away from lipids?
To decrease the risk of metabolite signal intensity being swamped by the higher lipid and water concentrations.
How is the voxel position selected?
Using a slice-selective RF pulse combined with magnetic field gradients.
Similar to slice selection in MRI
Characteristics of SHORT echo times:
- Better signal to noise ratio
- TE = 35ms
- Complicated baseline due to macromolecules and lipids that make quantitation more difficult
Characteristics of LONG echo time:
- 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
Main metabolites detected by proton MRS:
- Myo-inositol
- Choline
- Creatine
- Glutamate/Glutamine
- N-acetyl aspartate (NAA)
- Lactate and Lipids
What has the most prominent peak in proton brain spectra?
- N-acetyl asparate (NAA)
NAA is considered to be a marker of _________ _________.
neuronal integrity
Where is N-acetyl asparate (NAA) synthesized?
In the mitochondria.
What is the function of NAA?
The function of NAA is not yet known.
What are the primary theories of the function of NAA?
- Possibly an organic osmolyte
- Possibly involved in myelin/lipid synthesis
- Precurser for neurotransmitter NAAG
- Storage form for asparate
- Linked to metabolic efficiency
Are levels of creatine higher in grey matter or white matter?
Grey matter.
What is creatine’s role in the brain?
- Involved in energy metabolism
- Constant between individuals and brain regions
Decreased levels in creatine result in ____ _____.
cell death.
____ ______ can increase levels of creatine.
Head trauma
Decreased levels of creatine could be caused by ________ __________.
creatine deficiency.
Creatine deficiency could be a result of
- defects in synthesis or transport
What is Myo-inositol?
A simple alcohol sugar.
Myo-inositol is involved in _______ __________.
osmotic regulation.
What is Myo-inositol used as?
An astrocyte or glial cell marker.
When do Myo-inositol levels increase?
- Some dementia
- HIV infection
- Infancy
Glutamate and glutamine is denoted glx when _____________________________.
the combined glu/gln is measured as a result of low field peaks overlapping.
What is one of the most abundant compounds detected with proton MRS and is released by about 90% of excitatory neurons?
Glutamate
____ is an __________ neurotransmitter whose peaks overlap the peaks from glutamate and glutamine.
- GABA
- inhibitory
_______ is a doublet which means it has two peaks.
Lactate
Lactate peaks are inverted/upside down at ____________ echo times.
intermediate
_________ lactate levels are seen in hypoxia and ischaemia, mitochondria disorders, and some types of tumours.
Increased
Lipids in the range of ___ to ___ ppm should not be seen in the normal brain.
0.9 to 1.5 ppm; are seen in some tumours
