PET Scans

Question 1

What does PET stand for?

Answer 1

Positron emission tomography

Question 2

Define a tracer

Answer 2

A tracer is typically a biological substance which has a known behaviour in the body

Question 3

Define half-life

Answer 3

The length of time it takes for the radioactive activity to decrease by half.

Question 4

Is a PET scan functional or anatomical?

Answer 4

Functional (metabolic)

Question 5

What is the abbrev. for Fludeoxyglucose?

Answer 5

FDG

Question 6

For PET scans, what important ‘label’ is added to a tracer?

Answer 6

Labelled with a radioactive substance.

Question 7

What parts of the human body always tend to show up as ‘hot’ on a PET scan?

Answer 7

Brain
Kidneys
Bladder
Brown fat

Question 8

Why can tumours be identified by PET scans?

Answer 8

Because they tend to be metabolically active

Question 9

What is underneath a PET scanner?

Answer 9

A ring of detectors

Question 10

How does a PET scan using F-18 work?

Answer 10

• Radioactive Tracer uptake at sights of metabolic activity
• F-18 is radioactive and will decay with Positron emission (a positively charged electron)
• Positron will move a very short way before annihilation with electron (within 1mm)
• Characteristic behaviour of annhilation is
  2x 511keV photons emitted (gamma rays) in opposite directions to conserve momentum
• Detectors pick-up simultaneous photons and reconstruct where they were emitted

Question 11

keV of photons (gamma rays) emitted in each direction during annhilation?

Answer 11

511keV

Question 12

How can detectors detemine the original location of F-18?

Answer 12

Since the photos are emitted in opposite directions, the detectors can pick up simultaneous photons are determine the middle point.

Question 13

What is the main area of development in PET scans?

Answer 13

The number of detectors

Question 14

Why combine a PET scan with a CT scan? (PET-CT)

Answer 14

PET is purely functional

Combine PET with the anatomical information of CT

Question 15

List 4 applications of PET-CT scans

Answer 15

Brain imaging
Cardiology
Pharmacokinetics
Oncology

Question 16

Which application is the most common use of PET-CT scans?

Answer 16

Oncology (90%)

Question 17

Disadvantages of PET-CT

Answer 17

• Scan dose
• Low spatial resolution (limits how well can localise activity in the body)
• Scan is long, so risk of motion and image blurring/misalignment

Question 18

Type of radioactive decay of F-18?

Answer 18

Positron emission

emits a proton/positively charged electron

Question 19

In annihilation, why are 2 photons emitted (gamma rays) in opposite directions?

Answer 19

To conserve momentum