Scintigraphy Explained

Scintigraphy (from the Latin scintilla – spark) is a diagnostic imaging procedure used in radiology to detect long-lasting functional processes. To create a scintigram, tracer substances must be administered (this radiopharmaceutical is a chemical substance that has been labeled with a radiologically active substance so that an accumulation of the tracer in the tissue is achieved, through which the function of the respective organ can be checked. By the classical static scintigraphy it is not possible to look at organ functions which change within the examination process, because the production process of the scintigram can take up to half an hour. However, planar scintigraphy is suitable for registering metabolic activity in the organ structures of the body, as it produces an image that depicts multiple planes. The development of scintigraphy is largely due to the inventors of the gamma camera, Kuhl and Edwards, who presented it in a 1963 paper.

The process

The principle of scintigraphy is based on imaging metabolically active organ systems of the body using tracer substances that disperse into the body after absorption. These applied tracer substances are radioactive and thus emit gamma radiation into the environment. The radiation is measured with the help of a gamma camera, which is located above the organ to be examined and can record the activity distribution. The use of so-called collimators is indispensable for the function of the gamma cameras, as these can bundle the emitted radiation. In addition to the bundling effect, collimators also serve to select the radiation, since obliquely incident photons are absorbed by the apertures. The collimators increase the sensitivity of planar scintigraphy at a defined penetration depth. Due to the possible overlapping of imaging planes in scintigraphy, pathological functional changes are often only detectable from a size of more than 1 cm. In planar scintigraphy, technetium preparations are often used as radiopharmaceuticals because they are transported in the bloodstream but are not integrated into metabolic processes. The gamma radiation emitted is now converted into light flashes by scintillation crystals located in the gamma camera. An electronic signal is generated by a calculation process, which results in the degree of blackness in the scintigram. Scintigraphy is divided into several systems:

  • Static scintigraphy: this method is a supergroup consisting of hot-spot scintigraphy and cold-spot scintigraphy. However, an exact demarcation of the two methods is not always possible, so that the term static scintigraphy is often used.
  • Cold spot scintigraphy: this procedure is mainly used for imaging non-pathological tissues. With the help of cold spot scintigraphy, it is possible to ensure an accurate assessment of an organ regarding the size, location and shape. Furthermore, the procedure is also a potent diagnostic tool in pathological space-occupying processes with existing storage defects (cold spots). The procedure is of particular diagnostic importance in the examination of myocardial and cerebral perfusion and in the detection of pulmonary embolism. The particularly superficial glandula thyroidea (thyroid gland) represents an optimal object of investigation, in which pathological changes from 5 mm can be detected.
  • Hot-spot scintigraphy: in contrast to cold-spot scintigraphy, this method uses radiopharmaceuticals, which accumulate primarily in metabolically active areas. Due to this, this method is used to detect pathological processes. There is no minimum size of the pathologically altered area, since the detection of this structure depends almost exclusively on the activity of the tissue. As a result, hot spot scintigraphy is the early detection method of choice for many diseases with regionally limited changes. As further indications for hot spot scintigraphy are particularly tumors and possible metastases as well as thrombi and thyroid nodules.
  • Sequential scintigraphy: as another superset of scintigraphy, this method represents a distinction from static scintigraphy, since in the latter only a state of activity can be imaged that has reached equilibrium and that this state hardly changes, if at all. Additional dynamic information concerning several phases of the metabolism cannot be collected by the static method. Only sequence scintigraphy can image processes such as the perfusion of an organ. Often it requires a precise assessment of the functional impairment of an organ system, which is only possible through additional computer processing of the results.

In addition to conventional scintigraphy, there is also the possibility of using a method based on the basic principle of scintigraphy, single photon emission computed tomography (SPECT). The advantages of scintigraphy over SPECT scanning include the following:

  • The duration of the SPECT scan is nearly one hour for a whole-body scan. The scintigraphic scan requires only about half the time.
  • Furthermore, conventional scintigraphy is the more cost-effective procedure.

The disadvantages of scintigraphy compared to SPECT scan are the following:

  • Because of the greater depth of penetration, it is easier to diagnose deeper foci of disease. Moreover, the resolving power is considered better regardless of the depth of the tissue structure of the SPECT scan to be examined.
  • Furthermore, the spatial assignment of the structures in the scintigraphy is much more difficult than in the SPECT scan.

The following scintigraphy methods are known, among others:

The indication areas (application areas) are shown with each method.