Nuclear medicine

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Patient under gamma camera (thyroid scintigraphy).

Nuclear medicine is the use of open radionuclides for diagnostic and therapeutic purposes. It also includes the use of other radioactive substances and nuclear physical processes for functional and localization diagnostics and radiation protection with its physical, biological and medical principles.

“In vivo” method

In vivo methods are measurement methods in which a radiopharmaceutical (“ tracer ”) is introduced into the body, the gamma radiation or annihilation radiation of which can be measured very precisely from outside the body. (In some cases, additional information about organ functions is also provided by radioactivity measurements from blood samples or excretions.)

A radiopharmaceutical is a radionuclide or the chemical compound of a radionuclide with other substances. How a radiopharmaceutical is used in nuclear medicine depends essentially on two properties:

Diagnosis

The imaging processes scintigraphy , positron emission tomography (PET) and SPECT ( single photon emission computed tomography ) mainly depict the function of an organ or organ system according to the tracer principle , in contrast to the morphological imaging processes, which mainly show the structure . For example, a radiopharmaceutical ( 99m technetium methylenediphosphonate) is used in skeletal scintigraphy , which is preferentially absorbed by bone-forming cells ( osteoblasts ). Normal bone tissue shows low activity in the resulting scintigram, which results from physiological remodeling processes. Zones of increased activity, on the other hand, indicate increased bone remodeling and thus pathological processes that take place at the corresponding points in the skeleton. These can be contusions , healing fractures , cancer , benign bone tumors, arthritis or bone inflammation .

Dynamic studies are another example of the functional character of nuclear medicine. For example, kidney function scintigraphy records a series of images at intervals of between one and 60 seconds over a period of 20 to 40 minutes. In this way, the accumulation and excretion of the radiopharmaceutical in various organs can be recorded as curves. This makes it possible, for example, to assess the elimination performance of one kidney in relation to the other.

The field of nuclear medicine also includes the detection and medical evaluation of radioactivity that has entered the body in radiation accidents or of the natural potassium-40, which is proportional to muscle mass. Non-imaging measuring methods (scintillation detector, semiconductor detector, whole-body counter and excretion measurements) are available for this.

The most common nuclear medical examination procedures are thyroid scintigraphy , skeletal scintigraphy , myocardial scintigraphy , kidney function scintigraphy and lung scintigraphy as well as positron emission tomography . Nuclear medicine examinations exist for many other physiological processes.

Magnetic resonance tomography (also known as magnetic resonance imaging) and magnetic resonance spectroscopy are available as examination methods that are independent of ionizing radiation and that use nuclear physical effects to generate images of the interior of the body and to analyze the composition of tissues . However, their ability to make statements is not as pronounced in the functional area as in classical nuclear medicine, but more in the anatomical, whereby the hydrogen content of tissues primarily provides additional, functional, information. This method is practiced by qualified radiologists and, more rarely, nuclear medicine specialists.

Since nuclear medicine examinations often lead to anatomically ambiguous findings (i.e. the examiner sees a deviation from the norm, but cannot exactly assign it to a specific body structure, such as a lymph node group), more and more combination devices have been offered and set up since around the year 2000 , in which a nuclear medicine gamma camera or a PET scanner is combined with a mechanically permanently connected computer tomograph . Functional as well as anatomical data can be collected in one corridor without repositioning and merged in a set of images. This improves the clarity and, in various critical cases, the correctness of the diagnosis. Such devices are called SPECT-CT or PET-CT ; Fully integrated solutions are being worked on, and today (2012) the first PET / MRI devices - still mainly used in research - are available . The clinical value of PET-MRI cannot yet be assessed.

therapy

In nuclear medicine therapy, radiopharmaceuticals are used that emit beta or, more rarely, alpha radiation . These types of radiation are characterized by a low penetration depth (a few millimeters for beta radiation, a few µm for alpha radiation). As a result, they develop their effect at the place of accumulation in the organism. The kinetics of the radiopharmaceutical determines where this enrichment takes place. Radioiodine therapy , for example, targets the thyroid . The radiopharmaceutical is preferably absorbed by hormone-producing follicle cells and locally destroys excess or malignant tissue (see also hyperthyroidism , thyroid carcinoma ). Radioiodine is usually administered orally in the form of a therapy capsule.

Another possibility is the administration of artificially produced monoclonal antibodies or peptides (small protein molecules) provided with a suitable radionuclide . Such a radiopharmaceutical can be injected intravenously and finds its target organ “by itself”.

If the target organ is spatially well delimited and accessible, the direct introduction of the therapeutic radionuclide is recommended ( endoradiotherapy ). One such procedure is radiosynoviorthesis , which is increasingly being used for rheumatoid arthritis , activated arthrosis or other joint diseases. Yttrium-90 or another beta emitter is injected into the joint space to obliterate the synovial membrane.

The use of gamma radiation from enclosed radioactive substances, brachytherapy , is not counted among the nuclear medicine procedures.

"In-vitro" method

When in vitro methods laboratory methods such as the radioimmunoassay designated (RIA). With these methods, substance concentrations in sample material obtained from the body can be determined particularly precisely by means of immunological reactions, since a reaction partner was previously radioactively marked.

The specialist in nuclear medicine

In order to work as a specialist in nuclear medicine after completing a medical degree in Germany , five years of further training are required,

  • of which one year in inpatient care,
    • 6 months of which can be completed in another area
  • one year in radiology can be credited.

The further training regulations prescribe certain minimum numbers for examinations and therapies. Special courses in radiation protection must also be completed before the specialist examination.

literature

  • H. Götte, G. Kloss: Nuclear Medicine and Radiochemistry. In: Angew. Chem. 85th year, No. 18, 1973, p. 793.
  • Michael Feld: Nuclear Medicine. In: Werner E. Gerabek , Bernhard D. Haage, Gundolf Keil , Wolfgang Wegner (eds.): Enzyklopädie Medizingeschichte. de Gruyter, Berlin / New York 2005, ISBN 3-11-015714-4 , pp. 1058-1060.

Web links

Wikibooks: Physical basics of nuclear medicine  - learning and teaching materials

Individual evidence

  1. ↑ Erich Oberhausen et al.: Technology of nuclear medicine. 4th edition. Deutscher Ärzte-Verlag, Cologne 1990, ISBN 3-7691-1089-7 , p. 9.