Lecture 8: PET

Question 1

Give three isotopes used in PET and their HLs? (3 marks)

Answer 1

• C-11 20mins
• O-15 2mins
• F-18 110mins

Question 2

How does a PET scanner work and what corrections are applied when imaging? (9 marks)

Answer 2

Sketch this one…

PET imaging:

• following B+ decay, the positron annihilates with a nearby electron producing two gammas.
• uses a ring detector, which detects the 511 keV gammas emitted in opposite directions from the annihilation events.
• detector uses TOF to localise the position along the LOF from which the annihilation event occurred.
• detector is usually a similar crystal to a gamma camera.

Corrections applied:

• Flat fielding to correct for variations in pixel sensitivity.
• Missing photons correction from dead-time effects
• Attenuation corrections from CT data.

Question 3

What are the main PET applications and the isotopes used for those investigations? (6 marks)

Answer 3

• Cancer diagnosis using FDG
• Dementia using FDG
• Heart blood flow (Rb82 blood flow and FDG for metabolism)

Question 4

When is Ga-68 used in PET imaging and how does it decay? (6 marks)

Answer 4

Used for prostate cancer imaging with PMSA, decay via B+:

68Ga31 -> 68Zn30 + B+

Question 5

When is Rb82 used and give two advantages of using this over MPI with Tc-99m? (3 marks)

Answer 5

• Used for blood flow as it binds to RBCs

- Pros are lower cost and effective dose

Question 6

Give two recent advances are there in PET? (4 marks)

Answer 6

• Use of TOF to more accurately localise annihilation events along the LOR.
• Analysing the PSF to determine the direction of the gamma ray more accurately

Question 7

What are the pros and cons of PET-MR? (6 marks)

Answer 7

Cons: expensive and comprimise on the PET and the MRI aspects of the scans, not everyone can have an MRI.

Pros: lower dose compared to PET-CT, better soft tissue contrast compared, increased structural knowledge from MRI and functional knowledge from PET, MRI can be used for motion correction during scanning.