MI: PET

Question 1

PET Isotopes: What is the half-life of C-11?

Answer 1

20min

Question 2

PET Isotopes: What is the half-life of O-15?

Answer 2

2min

Question 3

PET Isotopes: What is the half-life of F-18?

Answer 3

110min

Question 4

PET Isotopes: What is the half-life of Ga-68?

Answer 4

68min

Question 5

PET Isotopes: What is the half-life of Cu-64?

Answer 5

12.7hrs

Question 6

PET Isotopes: What is the half-life of Zr-89?

Answer 6

3.17days

Question 7

How is a signal produced in a PET scan?

Answer 7

Positron released from the nucleus.
Annihilates with an electron.
Annihilation creates two gamma-rays (511keV each) travelling in opposite directions.
PET scanner detects gammas and uses time difference of events to calculate the position of annihilation.

Question 8

How is a cyclotron used to generate PET isotopes, and which isotopes is it commonly used to generate?

Answer 8

High energy particles fired at a target (commonly negative H- ions).
Used for low Z isotopes (C-11, F-18 etc.)

Question 9

How is a generator used to produces PET isotopes, and which isotopes is it commonly used to generate?

Answer 9

Different isotope with long half-life decays to produce positron emitter.
Ge-68 - t1/2 = 271 days decays to form Ga-68 - t1/s = 68mins.
Only suitable for certain isotopes.

Question 10

What are the properties of a radiotracer?

Answer 10

Traces the biochemical pathway, physiological function or fate of a drug.
May be identical to a natural compound.
High specific activity not required.
Needs to be selective for metabolic pathway or studied process.
Used in Pharmacokinetic studies - metabolism needs to be understood.
Labelling in more than one position - greater understanding.

Question 11

What are the properties of a radioligand?

Answer 11

Targets high-affinity binding sites.
Based on synthetic compounds
High specific activity required.
Selective for target site.
Little to no metabolic interference.

Question 12

Why is fluorine used as a radiotracer?

Answer 12

Fluorine has a longer half-life than carbon-11 - so useful for slower biochemical processes.
C-F bonds are stronger than C-H bonds - Enzymatic cleavage gives non-toxic fluoride.
Many drugs contain fluorine - increased bioactivity and lipophilicity.
It’s a steric mimic for -OH or H so can be accepted as an enzyme substrate with no reaction.