Fill in the blank: May 2017

What are some notable differences between PET and SPECT?

See: What are the indications for PET vs. SPECT?

• In contrast with PET however the tracer used in SPECT emits gamma radiation that is measured directly whereas PET tracer emits positrons that annihilate with electrons up to a few millimeters away causing two gamma photons to be emitted in opposite directions.

• A PET scanner detects these emissions "coincident" in time which provides more radiation event localization information and thus higher spatial resolution images than SPECT (which has about 1 cm resolution).

• SPECT scans however are significantly less expensive than PET scans in part because they are able to use longer-lived more easily-obtained radioisotopes than PET.

How are SPECT and PET similar?

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How are SPECT and PET similar?

Answer: SPECT is similar to PET in its use of radioactive tracer material and detection of gamma rays.

What are the indications for PET vs. SPECT?

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What are the indications for PET vs. SPECT?

SPECT (Single Photon Emission Computerized Tomography)

• Monitors level of biological activity within a 3-D region.

• Cane be used to complement any gamma imaging study where a true 3D representation would be helpful
(e.g.
1. tumor imaging.
2. infection (leukocyte) imaging.
3. thyroid imaging.
4. bone scintigraphy).

• Can be used to provide information about localised function in internal organs (e.g. functional cardiac or brain imaging).

Examples:

• Bone scan (where bone is being created or destroyed).

• White cell scan.

• Myocardial Perfusion scan (Diagnosis of ischemic heart disease).

• Sestamibi parathyroid scan.

• Brain scan (primarily cerebral blood flow).

• Neuroendocrine tumor.

PET = Positron Emission Tomography

o Nuclear/functional imaging of functional processes within the body.

o Main indication = cancer metastasis (90% of scans).

o May also be used for neuroimaging cardiac pharmacodynamics etc.

PET is a nuclear medicine/functional imaging.

• 3D image of functional processes in the body.

• Accompanied by a CT X-ray scan performed on the patient during the same session allowing for anatomic localization.

• Detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer) which is introduced into the body on a biologically active molecule [fludeoxyglucose (FDG)] the concentrations of tracer imaged will indicate tissue metabolic activity by virtue of the regional glucose uptake.