6.2. Nuclear medicine - Positron Emission Tomography

What is PET scanning?

A diagnostic test in nuclear medicine that uses radioisotopes in the form of radiopharmaceuticals to visualise and measure how tissues and organs function at a cellular level

What is the most common radiopharmaceutical used in PET?

Fluorodeoxyglucose (FDG), used in approximately 90% of scans

What does PET visualise and measure?

How tissues and organs work at the cellular level, changes in metabolic processes, blood flow, regional chemical composition, and absorption

How are signals detected in PET scanning?

Gamma photons are detected due to electron-positron annihilation

What is electron-positron annihilation?

When an electron and its antiparticle (positron) meet and annihilate each other, producing two gamma photons (e- + e+ → γ + γ)

What does FDG stand for?

Fluorodeoxyglucose

What is a positron?

The antiparticle of an electron — same mass, opposite electrical charge, produced naturally in certain types of radioactive decay

How does FDG work in PET scanning?

It is taken up by glucose transporters in cells; areas of high metabolic activity absorb more FDG and appear bright

Why do cancer cells show high FDG uptake?

They multiply rapidly and do not undergo programmed cell death, so they absorb far more FDG

What does low FDG uptake indicate?

Areas of low metabolic activity, often caused by obstruction of blood flow

What cardiac conditions can FDG-PET detect?

Cardiovascular disease, hardening of arteries, and stroke risk prediction

What brain conditions can FDG-PET detect?

Alzheimer's disease, haematomas, epilepsy, and tumours

What lung conditions can FDG-PET detect?

Tumours and infection

What is combination scanning in PET?

Combining PET with CT or MRI to provide both anatomical and metabolic information in precisely matched images

What are the advantages of PET scanning?

Functionality at cellular level due to metabolic changes, can compare between different metabolic states such as rest vs stress (heart), 3D images produced, painless, considered non-invasive

What are the disadvantages of PET scanning?

Misalignment of images, false negatives possible (low FDG in low-volume or low-metabolic-rate tumours), and risk of misdiagnosis of metabolic changes

Which of the following is an advantage of PET as an imaging modality:

A comparison is possible between different metabolic states

The following PET image is indicative of:

A diffuse infection