Magnetic Resonance Spectroscopy (MRS) of the Brain

Question 1

What techniques use magnetic resonance (MR) phenomena?

Answer 1

• Nuclear Magnetic Resonance (NMR) Spectroscopy
• Magnetic Resonance Spectroscopy (MRS)
• Magnetic Resonance Imaging (MRI)

Question 2

What are the characteristics of Nuclear Magnetic Resonance (NMR) Spectroscopy?

Answer 2

• Chemical analysis
• Structural elucidation of compounds and macromolecules
• Chemical composition of solutions

Question 3

What is observed in an MRS?

Answer 3

Metabolites in a volume, or voxel.

Question 4

What is observed in an MRI?

Answer 4

Water protons whose magnetic properties change depending on its environment.

Question 5

What happens to a proton in a magnetic field?

Answer 5

Can either spin up or spin down.

Question 6

Which proton has lower energy?

Answer 6

Spin up protons.

Question 7

Which proton has higher energy?

Answer 7

Spin down protons.

Question 8

True or False: Protons resonate at different frequencies due to the presence of chemically bonded electrons.

Answer 8

True

Question 9

How does spin-spin coupling occur?

Answer 9

Arises from interactions between adjacent bonded magnetic nuclei.

Question 10

Spin-spin coupling is also called:

Answer 10

• Scalar coupling

- J-coupling

Question 11

How is scalar coupling (spin-spin coupling) measured?

Answer 11

• In hertz (is field independent)

Question 12

In spectroscopy, higher ________ _____ _________ result in greater __________ of the __________, thus making it easier to resolve them.

Answer 12

• magnetic field strengths
• dispersion
• resonances

Question 13

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

Answer 13

b. Number of protons.

Question 14

Reference Concentration:

_________ allows us to measure absolute metabolite concentration.

Answer 14

A reference

Question 15

When is a measurement of absolute concentration possible?

Answer 15

When a water spectrum is acquired; as long as we know the tissue/water concentration.

Question 16

True or false: Concentrations of metabolites are higher than concentrations of water and lipids/

Answer 16

False. Concentrations of waters and lipids are much higher than some of the metabolites.

Question 17

Metabolite signal intensity risks being ___________ by the relatively higher intensity of lipids and water.

a. swamped
b. increased

Answer 17

a. swamped

Question 18

Why is the water signal suppressed and voxels suppressed away from lipids?

Answer 18

To decrease the risk of metabolite signal intensity being swamped by the higher lipid and water concentrations.

Question 19

How is the voxel position selected?

Answer 19

Using a slice-selective RF pulse combined with magnetic field gradients.

Similar to slice selection in MRI

Question 20

Characteristics of SHORT echo times:

Answer 20

• Better signal to noise ratio
• TE = 35ms
• Complicated baseline due to macromolecules and lipids that make quantitation more difficult

Question 21

Characteristics of LONG echo time:

Answer 21

• 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

Question 22

Main metabolites detected by proton MRS:

Answer 22

• Myo-inositol
• Choline
• Creatine
• Glutamate/Glutamine
• N-acetyl aspartate (NAA)
• Lactate and Lipids

Question 23

What has the most prominent peak in proton brain spectra?

Answer 23

• N-acetyl asparate (NAA)

Question 24

NAA is considered to be a marker of _________ _________.

Answer 24

neuronal integrity

Question 25

Where is N-acetyl asparate (NAA) synthesized?

Answer 25

In the mitochondria.

Question 26

What is the function of NAA?

Answer 26

The function of NAA is not yet known.

Question 27

What are the primary theories of the function of NAA?

Answer 27

- Possibly an organic osmolyte - Possibly involved in myelin/lipid synthesis - Precurser for neurotransmitter NAAG - Storage form for asparate - Linked to metabolic efficiency

Question 28

Are levels of creatine higher in grey matter or white matter?

Answer 28

Grey matter.

Question 29

What is creatine's role in the brain?

Answer 29

- Involved in energy metabolism | - Constant between individuals and brain regions

Question 30

Decreased levels in creatine result in ____ _____.

Answer 30

cell death.

Question 31

____ ______ can increase levels of creatine.

Answer 31

Head trauma

Question 32

Decreased levels of creatine could be caused by ________ __________.

Answer 32

creatine deficiency.

Question 33

Creatine deficiency could be a result of

Answer 33

- defects in synthesis or transport

Question 34

What is Myo-inositol?

Answer 34

A simple alcohol sugar.

Question 35

Myo-inositol is involved in _______ __________.

Answer 35

osmotic regulation.

Question 36

What is Myo-inositol used as?

Answer 36

An astrocyte or glial cell marker.

Question 37

When do Myo-inositol levels increase?

Answer 37

- Some dementia - HIV infection - Infancy

Question 38

Glutamate and glutamine is denoted glx when _____________________________.

Answer 38

the combined glu/gln is measured as a result of low field peaks overlapping.

Question 39

What is one of the most abundant compounds detected with proton MRS and is released by about 90% of excitatory neurons?

Answer 39

Glutamate

Question 40

____ is an __________ neurotransmitter whose peaks overlap the peaks from glutamate and glutamine.

Answer 40

- GABA | - inhibitory

Question 41

_______ is a doublet which means it has two peaks.

Answer 41

Lactate

Question 42

Lactate peaks are inverted/upside down at ____________ echo times.

Answer 42

intermediate

Question 43

_________ lactate levels are seen in hypoxia and ischaemia, mitochondria disorders, and some types of tumours.

Answer 43

Increased

Question 44

Lipids in the range of ___ to ___ ppm should not be seen in the normal brain.

Answer 44

0.9 to 1.5 ppm; are seen in some tumours