Radioactive isotope, gamma camera, technetium - terms that do not necessarily produce positive associations. Wrongful: They are important components of nuclear medicine procedures and open up numerous diagnostic and therapeutic possibilities. The scintigraphy is one of them.
Principle of scintigraphy
Scintigraphy is an examination method in which images are generated by radioactive substances, mostly technetium (99mTc), which are incorporated into the body. This allows the metabolism and organ functions to be assessed and certain tissue changes to be recognized.
- Radionuclides (radioisotopes) are unstable atomic nuclei of chemical elements that break down easily and release radioactive radiation.
- If such substances are bound to carriers ("radioactive labeling"), a radiopharmaceutical is produced which can be introduced into the organism as an injection, tablet or respiratory gas. It disperses in the body and then - depending on the degree of accumulation - temporarily emits different levels of radiation. This can be registered with the help of a so-called gamma camera and converted by computer into pictures (scintigrams).
- As carrier materials, chemical compounds are used which are known to be incorporated into specific organs so that they can be specifically examined. For example, pertechneate is suitable for the diagnosis of the thyroid, since it is absorbed by it like iodine.
Very rapidly disintegrating radionuclides and readily precipitable carriers are used, so that the duration of action of the radioactivity is limited to minutes to hours and thus the radiation exposure to the patient is very low (usually not higher than the conventional X-ray images). Nevertheless, the examination should be carried out during pregnancy and lactation only in exceptional cases. The excretion of the radioactive degradation products via the kidneys can be accelerated with increased fluid intake following the examination.
Shapes of scintigraphy
Scintigraphy is great for testing tissues for their ability to function, even before any visible changes occur. In principle one differentiates the static and the dynamic Szintigrafie. The first one can assess the location, shape, size and mass of tissue and detect abnormalities such as inflammation or tumors. The actual organ function can be assessed by means of dynamic scintigraphy. Sequential and functional scintigraphy are used as techniques for this:
- Static scintigraphy: Here, similar to a normal x-ray, one or more images are taken at one time, sometimes in two planes, to better visualize the three-dimensional distribution of the radiopharmaceutical. For functional analyzes, this form is used when the state of the activity distribution is stable and lasts for a relatively long time. Regionally either a normal, a reduced or missing activity enrichment (memory defect, "cold spots") or an increased storage ("hot spots") can be recognized.
- Sequence scintigraphy: If the distribution of radionuclides changes quite rapidly and over and over again (eg in the excretion of urine via the urinary tract), several images are taken at fixed intervals (eg every minute) to assess the course of the process.
- Function scintigraphy: Combining the sequence scintigraphy with a computer-controlled calculation of the radiation activity, conclusions can be drawn on the functioning of whole organs or their parts. This can be helpful in particular for comparing the sides of blood circulation or organ function (eg kidneys, brain halves).
Emission computer tomography (ECT) is based on a similar principle as scintigraphy. Again, a radiopharmaceutical (usually fluorodeoxyglucose) is injected. The emitted radiation is then recorded by means of rotating cameras or ring detectors and - this is the main difference - converted by the computer into sectional images (computed tomography). Single-photon emission computer tomography (SPECT) also uses gamma emitters, while positron emission tomography (PET) uses short-lived positron emitters. The latter are extremely expensive, so the investigation is only carried out in large centers.
Expiration of a scintigraphy
Whether a preparation of the patient is necessary, depends on the examined organ and the examination method. Sometimes the patient needs to stay sober, stop taking certain medications or drink more.
The examination is carried out lying or sitting. The most unpleasant is the most necessary syringes of the radiopharmaceutical. The gamma camera is mounted on a motorized tripod, bypasses the patient and takes pictures at intervals of seconds or minutes. For this the patient - depending on the question and the device - has to keep still for 10 to 30 minutes. Scintigraphy can take anywhere from a quarter of an hour (for a shot) to several hours.