Nuclear Medicine

Question 1

What is the typical diagnostic administered activity range?

Answer 1

kBq - MBq

Question 2

What are the basic principles of PET?

Answer 2

1. Beta+ emitter administered
2. Beta+ travel ~mm in patient
3. Beta+ collides with electron and forms positronium
4. Positronium decays into 2 511keV back-to-back gamma rays
5. Gamma rays are detected by a ring of crystals
6. Energy window used to confirm gamma rays are 511keV (i.e. not from scatter)
7. If detected within ~ns, assume same event

Question 3

What are the problems with using CT data to account for PET attenuation?

Answer 3

CT and PET use different photon energies which mean that attenuation properties are different

Question 4

Why is energy resolution of a gamma camera important?

Answer 4

To distinguish true events from (Compton) scattered events

Question 5

How is energy resolution of a gamma camera defined?

Answer 5

Measure of the ability of the detector to discriminate different gamma ray energies

ER = FWHM/Photopeak energy

Question 6

Why is energy resolution of a gamma camera important?

Answer 6

To distinguish true events from (Compton) scattered events

Question 7

What is the typical therapy administered activity range?

Answer 7

MBq - GBq

Question 8

What is Nuclear Medicine?

Answer 8

Administer activity for diagnosis or therapy, and observe the emitted radiation outside the body (diagnosis) or deliver targeted energy deposition within the body (therapy)

Question 9

What are the properties of an ideal diagnostic radionuclide?

Answer 9

1. Half-life - long enough for transport but not too long causing excess dose
2. Ability to bind to a pharmaceutical and not too expensive
3. Suitable energy emission for detection without too much dose
4. Toxicity and chemistry

Question 10

What is the purpose of a gamma camera collimator?

Answer 10

There is no directional information in the crystal detection meaning the image has a poor PSF. Using a collimator accepts only the gamma rays normal to the crystal and filters out those that are not normal to the crystal. This improves image quality but reduces sensitivity.

Question 11

What types of gamma camera collimators are there?

Answer 11

Parallel hole
Diverging hole
Pinhole
Converging hole

Question 12

What is the effect of resolution if the diameter of the gamma camera collimator hole inreases?

Answer 12

Worse resolution

Question 13

What is the effect of resolution if the length of the gamma camera collimator septa inreases?

Answer 13

Better resolution

Question 14

What is the effect of resolution if the distance from the gamma camera collimator inreases?

Answer 14

Worse resolution - position patient as close as possible to detector

Question 15

What does the spatial resolution of a gamma camera depend on?

Answer 15

Intrinsic and extrinsic resolution (and scatter)

Question 16

What does the intrinsic resolution of a gamma camera depend on?

Answer 16

Light spread and Anger logic

Question 17

What does the extrinsic resolution of a gamma camera depend on?

Answer 17

Collimator design (length, width, distance)

Question 18

What is meant by the term end-point energy?

Answer 18

The endpoint energy is the maximum energy that can be given to the electron, and that is closely related to the reaction Q-value

Question 19

List the properties of 18F that make it optimal for diagnostic imaging in nuclear medicine.

Answer 19

Half-life - short but not too short for uptake and imaging
Emissions - emits positrons which annihilate into gammas with an energy that can be measured by camera
Can bind to pharmaceuticals
Easily available