PET

-Positron Emission Tomography

What Is PET?

• Nuclear medicine scan, Functional imaging technique.

• Quantifiable – amount of radiation depends on rate of metabolic activity

• non-invasive, but does involves exposure to ionizing radiation,

• Usage of radioactive isotopes (radiopharmacons) emitt β⁺ particles

How Does PET Work?

• Administration of radiopharmacon

• Decay of isotope internally, accumulation of

radiopharmacon in diseased tissue.

• Electron interaction annihilation emission of 2 gamma photons.

• Scintillating detectors ( gamma camera).

• Collection and storage

of data reconstruction

of 2D distribution map.

• Most scans today are combined with CT.

Detection Of Emission

Collection Of Data – Lines Of Conicidence

Each detector can be operated in multiple coincidence with many detectors across from it.

Linear sampling – defining parallel coincidence sampling paths.

Radioactive Isotopes

Isotope 11C 13N 15O 18F

Half-life (minutes)

20.3 9.98 2.05 110

Nuclear reaction14N (p,α) 11C 16O(p,α) 13N 14N(d,n) 15O 18O (p,n) 18F

Common isotopes used for PET examinations and their main properties

Manifactured by cyclotrons. Cyclotron = accelerator with a circular path enforced by a magnetic field.

Medical Fields Of Application• PET and PET/CT scans are performed to:• detect cancer.• determine spread of cancer• Determine effectiveness of treatment, such as cancer therapy. • Detect return of a cancer. • determine blood flow to the heart muscle.• determine the effects of a heart attack, or myocardial infarction, on

areas of the heart.• Identification whether certain areas of the hear would or wouldn’t

benefit from surgery. • Evaluate brain abnormalities; tumors, memory disorders, seizures

and other central nervous system disorders.• To map normal human brain and heart function.

Medical Fields Of Application

PET Image Fusion Technique •Fusion of a PET scan with MRI, CT or alternative image

to give functional and anatomical information.

CT scan

PET scan

Fused PET and CT image

Benefits And Risks Of PET Benefits of PET:•Image information unique- high sensitivity •yields most useful information compared to other imaging techniques from a pathological view. •High spatial resolution• more precise, cheaper, and more esthetical than exploratory surgery. •Can detect a disease at an earlier stage than ex. CT scans or MRI. •Result in low radiation exposure. (obs. not more than any other type of imaging method!)

Risks with PET:•Allergic reactions to radiopharmaceuticals may occur but are rare. •Injection of the radiotracer may cause slight pain and redness which should rapidly resolve.•Expensive – due to cyclotrons needed to produce short lived radionuclides. •Low accecssbility • takes time