Neuroimaging

Question 1

What is the purpose of structural neuroimaging?

Answer 1

To study the architecture of the brain and detect any distortions to its structure.

Question 2

Which materials appear hypodense (dark) on a CT scan, and why?

Answer 2

Air and fluid because they are passed through easily by x-rays.

Question 3

Which materials appear hyperdense (bright) on a CT scan, and why?

Answer 3

Bone and metal because they are dense, so x-rays cannot easily pass through.

Question 4

What does CT stand for?

Answer 4

Computed tomography.

Question 5

How does a CT scan work?

Answer 5

X-rays create 2D images.

Question 6

Why is CT useful for detecting acute haemorrhage?

Answer 6

Haemorrhage appear hyperdense due to the x-ray absorption of iron within the haemoglobin of the blood.

Question 7

What does MRI stand for?

Answer 7

Magnetic resonance imaging.

Question 8

How does MRI work?

Answer 8

A magnetic field and radiofrequency pulses cause hydrogen atoms within the tissues to align and then relax.
The energy emitted by the hydrogen nuclei as they realign is detected and reconstructed into 2D images.
The 2D images are displayed as contiguous slices.

Question 9

Why is MRI the preferred structural neuroimaging modality over CT?

Answer 9

MRI provides much higher resolution images of soft tissue.

Question 10

What is the purpose of T1-weighted MRI images?

Answer 10

It uses specific radiofrequency pulses to highlight hydrogen atoms in more hydrophobic environments, such as myelin.

Question 11

How does white matter appear in T1-weighted images?

Answer 11

Bright/hyperintense.

Question 12

How does grey matter appear in T1-weighted images?

Answer 12

Dark/hypointense.

Question 13

How do lesions appear in T1-weighted images?

Answer 13

Dark/hypointense.

Question 14

What is the purpose of T2-weighted MRI images?

Answer 14

It uses specific radiofrequency pulses to highlight structures containing water rather than lipids.

Question 15

How does grey matter in T2-weighted images?

Answer 15

Bright/hyperintense.

Question 16

How does white matter appear in T2-weighted images?

Answer 16

Dark/hypointense.

Question 17

How do lesions appear in T2-weighted images?

Answer 17

Bright/hyperintense.

Question 18

What does MRS stand for?

Answer 18

Magnetic resonance spectroscopy.

Question 19

How is data from MRS represented?

Answer 19

As a waveform with peaks representing the presence and concentration of various metabolites in brain tissue.

Question 20

Why is MRS frequently used in neuro-oncology?

Answer 20

Neoplastic tissue is metabolically different from normal brain tissue.

Question 21

How can MRS be used clinically in neurodegenerative disorders?

Answer 21

Neurodegenerative disorders can cause abnormal ratios of certain brain metabolites.

Question 22

What does DTI stand for?

Answer 22

Diffusion tensor imaging.

Question 23

What is the purpose of DTI?

Answer 23

To assess the integrity of subcortical white matter pathways.

Question 24

What happens to subcortical white matter pathways when somebody has a destructive lesion (e.g. stroke) or a condition like Alzheimer’s?

Answer 24

They are disrupted or degraded.

Question 25

How does DTI work?

Answer 25

It combines voxel-based measurements of diffusion with information about the directionality or vector of restricted diffusion to create probabilistic maps of expected locations of white matter pathways.

Question 26

Why are fMRI and DTI important tools in neuropsychiatric research?

Answer 26

They provide information on the functional and structural connectivity of neural circuits involved in a variety of neurocognitive tasks.

Question 27

What does PET stand for?

Answer 27

Positron emission tomography.

Question 28

What does SPECT stand for?

Answer 28

Single photon emission computed tomography.

Question 29

What is a tracer?

Answer 29

A radioisotope that is coupled to a molecule of interest.

Question 30

How does PET work?

Answer 30

A tracer is injected into the bloodstream. It crosses the BBB into the brain. As the radioisotope decays, it emits radioactive particles (positrons) that can be detected. This allows areas of the brain in which the tracer has accumulated to be mapped.

Question 31

Name the two most commonly used radioisotopes.

Answer 31

(18F) fluorine. (11C) carbon.

Question 32

What is the most commonly used PET tracer?

Answer 32

18F-fluorodeoxyglucose (FDG).

Question 33

How does FDG work?

Answer 33

It is a radioactive analogue of glucose, so it is taken up and utilised by metabolically active neurons and other cells.

Question 34

What is the purpose of FDG-PET?

Answer 34

To provide a map of glucose utilisation of the brain.

Question 35

How do neurodegenerative diseases present in an FDG-PET?

Answer 35

They result in a reduced FDG-PET signal because they produce patterns of hypometabolism.

Question 36

Name the two abnormal proteins that accumulate in Alzheimer's.

Answer 36

Beta-amyloid. Tau.

Question 37

Why is 11C-Pittsburgh Compound-B (PiB) used as a tracer to detect Alzheimer's?

Answer 37

The radioisotope carbon-11 is coupled to a molecule that binds to beta-amyloid.

Question 38

What is the purpose of SPECT?

Answer 38

To detect cerebral blood flow.

Question 39

Which radiomolecule is used in SPECT?

Answer 39

Technetium.

Question 40

How does SPECT work?

Answer 40

A radiomolecule travels via the bloodstream to well-perfused areas of the brain. It emits gamma rays as it decays. This allows area of increased and decreased perfusion to be mapped.

Question 41

How does dementia present in SPECT?

Answer 41

There is reduced blood flow to atrophic regions.

Question 42

How can Parkinson's be detected using SPECT?

Answer 42

In Parkinson's, there is a decreased presence of dopamine transporters (DaTs) in the striatum and basal ganglia. Ioflupane-123 can be taken up by DaTs. There will be reduced tracer uptake in the striatum and basal ganglia.