Immunoscintigraphy

The Immunszintigrafie is an imaging technique in nuclear medicine. It is for diagnostic purposes, especially in oncology, as well as for the study of inflammation reactions, are used. Thereby radiolabeled monoclonal antibodies or fragments of antibodies can be administered to the patient and shown imagewise by means of a gamma camera. About the scintigram obtained, the progress of the disease, such as metastasis, are determined and on the therapeutic intervention building are planned. The Immunszintigrafie is a special form of scintigraphy.

Principle

Monoclonal antibodies and their fragments are able to bind highly specifically to certain proteins (antigens) on the cell membrane. These antigens are in morbid, especially in malignant cells (cancer cells ), the target structure ( target) for the antibodies (ligand). Antibody and antigen interact according to the key - lock principle. The antibodies can be labeled by means of radioisotopes. The radioactive label is used in the case of Immunszitigrafie only for diagnostic purposes. It only high-energy γ - emitter with high tissue penetration and short half-life ( maximum a few days) are used. Quite the contrary, β - emitters are used with a very short range in tissue in radioimmunotherapy substantially. The tracer obtained after labeling are generally considered immunoconjugates or in specific radioligand. If the radioligand administered to a patient, it is called a radiopharmaceutical. The radioligand are usually administered intravenously. The labeled antibodies to circulate in the body as long as possible, and ideally only bind to the target structures (antigens ) of the diseased cells. There, the antibodies accumulate in the subsequent period. Unbound antibodies circulate further in the body or excreted again after some time.

Also includes fragments of a monoclonal antibody, such as Fab, F (ab) 2 or scFv can serve as a support (carrier) for a radionuclide.

As radionuclides are, in general, the γ - emitters used in scintigraphy with a short half -life, such as Technetium -99m ( from a technetium generator ), gallium -67, indium-111 or iodine -123 is used. Polyvalent metals are often linked via a strong chelating agents such as DOTA to the carrier protein.

Application

The Immunszintigrafie is mainly used in oncology for cancer. Usually the Immunszintigrafie is used for the detection of recurrence after therapeutic interventions. The method is restricted to tumors or metastases with a diameter of about 10 mm. Smaller tumor foci are detectable only in exceptional cases. With the Immunszintigrafie can also check whether a patient will respond to a therapeutic antibody. Binds the diagnostic sufficient to cancer cells that may, in a subsequent therapy such as a radioimmunoconjugate be administered. With an insufficient connection such a therapy would be futile., Which consists of a monoclonal antibody and radioisotope radiopharmaceutical is administered intravenously most of the patients. After several hours, often 4 and 24, a bone scan is created. The acquisition time is generally between 30 and 90 minutes. Side effects are extremely rare. Incompatibilities, in the form of allergic reactions by the antibody ( foreign protein ), are possible. The radiation exposure equivalent to one to two CT scans.

In addition to oncological applications are also Immunentzündungsszintigraphien, but much less frequently performed. In this process of inflammation may be localized in the body of the patient, for example, with fever of unknown origin ( FUG ).

Example

Arcitumomab is a medicament on the basis of a fragment of a murine monoclonal antibody that is conjugated with the radioisotope 99mTechnetium. The immunoconjugate binds to carcinoembryonic antigen which is overexpressed in many colorectal carcinomas. Metastases or recurrences can be detected by this diagnostic by SPECT.

Immuno- PET

A variant of the immune Immunszintigrafie PET (immune positron emission tomography). Instead of a gamma emitter is a positron emitter, such as 68Gallium, used as a radionuclide. The emitted positron annihilates with an electron of the immediate vicinity of the radionuclide to two high energy gamma rays, which fly apart at an angle of 180 ° and can be detected. On the Principle of PET see Positron Emission Tomography. The immuno- PET has a number of advantages compared to the Immunszintigrafie such as a lower detection limit on. The method is still relatively new and only a relatively small spread.

Immunoscintigraphy

Principle

Application

Example

Immuno- PET

Further Reading