PET, SPECT and CT

PET

PET scans are acquired following administration of a radiotracer. The radiotracer accumulates in the tissue to be studied, and its radionuclide decays by emission of a positron (anti-electron). After travelling at most a few millimetres, a positron will collide with an electron, simultaneously releasing two gamma rays (photons) with an energy of 511 keV into opposite directions. These two photons are detected by the PET camera and simultaneously localized within a fixed period of time by a series of opposing detectors, which correspond to multiple rings of scintillation crystals. By collecting a statistically significant number of radioactive events, mathematical algorithms reconstruct a three-dimensional image that shows the distribution of the positron-emitting molecules in the brain. 

PET imaging uses isotopes which decay by β+, these usually have short half-life. This technique is advantageous for shorter processes and can also be used by multiple administrations of the tracer.

SPECT 

Gamma-ray photons emitted from the internal distributed radiopharmaceutical penetrate through the animal’s or patient’s body and are detected by a single or a set of collimated radiation detectors. Most of the detectors used in current SPECT systems are based on a single or multiple NaI (TI) scintillation detectors. In SPECT, projection data are acquired from different views around the animal/patient.

SPECT imaging uses photons emitted from radioactive decay, for photon energies 25-350 keV. These isotopes usually have longer half-life, and the technique is advantageous for long processes as well as radiotherapy studies. Due to the difference in photon energy from different isotopes, more than one process can be monitored simultaneously.

CT

X-ray Computed Tomography (CT) is a non-invasive technique for visualizing interior features within solid objects and for obtaining digital information on their 3-D geometries and properties. The same object can be imaged multiple times on different occasions to study the development of your treatment/disease model. CT uses the density difference in the object to create images of resolution down to 10 µm.

Using a radioactive tracer, physiological phenomena can be followed and functional images are created. The biomolecule of interest, labelled with a radioactive nuclide, is injected into the object to follow where it accumulates and how fast. The acquired intensity maps are then superimposed on the CT picture for easier image analysis. 

Instrument specifications

CT (Mediso)

NanoSPECT/CT (Mediso)

NanoPET/CT (Mediso)