Gamma Cameras

The most widespread of nuclear medical diagnostics

'Gamma cameras' or scintillation cameras are pieces of apparatus which allow radiologists to carry out 'scintigraphy scans', tests which provide detailed diagnoses about the functioning of the thyroid, the heart, the lungs and many other parts of the body. Scintigraphy scans get their name from the ability of some crystals (such as sodium iodide) to scintillate (in other words, emit sparks) when exposed to radiation.

Double-headed gamma camera
This gamma camera is equipped with two heads capable of detecting the presence of radiation. The lower head is partly concealed under the bed, and the whole apparatus can be moved along horizontally to obtain a full-body scintigraphy. By doubling the number of gamma rays used, a face scintigraphy can be performed at the same time as a back scintigraphy for the same amount of radioisotope ingested. By comparison with a PET scanner, a gamma camera requires much less equipment and is more easy to set up. A large number of hospitals make use of them for this reason.
CHU Avicenne

The procedure involves giving the patient a radiopharmaceutical molecule marked with a gamma-emitting radioisotope. Once the molecule fixed on the target organ or tissue, the highly penetrative emitted gamma rays easily escape from the body and leave their mark on the detection panels. The molecule which is followed around the body is carefully chosen with respect to the body part under examination. A very small quantity of radioactive isotope is all that is needed, as the detection systems are sensitive enough to register the decay of individual atoms.

Principles behind gamma-camera detection
In a gamma-camera, every atom that disintegrates emits a gamma photon. Once the photon leaves a mark upon colliding with a scintillator, the signal is amplified by a photomultiplier. Le photon direction has to be gauged by tracing the path back to the source. This is achieved by the lead canal collimators, which distinguish between photons going in different directions. In the diagram above, only photon A reaches the scintillator (and will therefore also be detected by the photomultipliers) while photons B and C are absorbed by the lead. For gamma rays emitted by technetium atoms, 140 keV of energy will be deposited in the scintillators.
André Aurengo, Hôpital Pitié-Salpêtrière

As its name indicates, a 'gamma camera' detects scintillations produced by gamma rays emitted by a radioactive marker. Once a large number of these scintillations have been observed, the radioactive molecules emitting these gamma rays can be located.

Thanks to computer technology, complex calculations can be performed very quickly to convert the detected radiation into information that is useful for radiologists. The images, created in a fraction of a second, allow doctors to follow the spread of the radioisotope throughout a patient's body in real time. This allows for highly detailed pictures of the heart contraction, or of the filtration of blood plasma in the kidneys. A gamma camera scintigraphy can also be used to form images of the skeleton, by injecting patients with a radioactive solution which attaches itself onto the bones. This is often how skeletal metastases are detected.

The scintillation camera was invented by the American physicist H.O. Anger in Berkeley in 1957. It has since revealed itself to be an irreplaceable tool in a wide range of different diagnoses. Unquestionably the preferred piece of equipment in the field of nuclear medicine, there were 14,000 of them in the world by 1996 and much more now.

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