Tracers are artificial endogenous or exogenous substances that are radioactively labeled to participate in the patient’s metabolic processes after being introduced into the body. Tracer is the English word for trace. Based on the traces and markings that the tracers leave in the body of the diseased patient, they enable and facilitate various examinations for researchers and radiologists. The synonym is radionuclide.
What are tracers?
The term tracer is assigned to nuclear medicine. This labeling substance in metabolic testing is a radionuclide (radioindicator) that is as short-lived as possible and causes a minimal radiation dose. The term tracer is assigned to nuclear medicine. This tracer substance in metabolic examination is a short-lived radionuclide (radioindicator) as possible, which causes a minimal radiation dose. This admixed tracer dose acts as a tracer substance in the human body through its registered radiation (RIA) to facilitate examinations and therapies of diseased patients. They are foreign or endogenous substances mixed with radioactive substances. The organ affinity component is responsible for the accumulation of these substances in the organs. The radionuclide enables the measurement of this enrichment process. It participates in the metabolic process (metabolism) of the organism and serves as a basis for diagnostics, therapy and research. Radionuclides introduced into the organism by foreign bodies are also called tracers, since they fulfill the same tasks. Tracers are supplied enriched with dosed units of organ affinity substances in the form of kits. The required radionuclide is admixed accordingly.
Function, effect, and goals
Internal radiation therapy uses tracers to deliver radioactive materials into the human body. On site, the radioindicators accumulate in malignant neoplasms (pathological, autonomous tissue proliferation of tumors) and lead to locally controlled cell death (apoptosis) or cell death by damaging the cell structure (necrosis) in the cancer cells. In this process, physicians must take into account that healthy cells are also destroyed. Modern medicine tries to minimize this risk by using so-called markers and special modifications to increase the selectivity between malignant and healthy tissue and thus spare the patient. Internal radiation therapy uses isotopes by emitting the low-energy, short-range ß-rays. If the patient has tumors in the rectum, nose, mouth, and uterus, radiologists prefer intraactive radiotherapy. Treatment is delivered by administering capsules laced with radionuclides to the affected organ cavities. There, the capsules gradually unfold their effect. The afterloading procedure involves the introduction of empty capsules, which are then filled with radioactive substances in the organism. The isotope 192Ir (iridium) is used here. Metabolic radiotherapy is the most widely used in research. It is based on injections of radionuclides bound to tracers. These act as carrier molecules capable of registering neoplasia and releasing the radionuclides at the affected sites. Selectivity increases by powers through this targeted use, sparing the patient and improving their chances of survival. Researchers are currently trying to advance this form of therapy to the point where synthetic carrier molecules are available for all types of malignant neoplastic tissue to release the radionuclide. If researchers are successful in their efforts, this approach will increase treatment efficiency and cure rates. Currently, radioiodine therapy is used with the 131I isotope (iodine, iodine). Doctors also used radioindicators in diagnostics. They are administered to patients to participate in metabolism in tissues or specific organs. Radioactively labeled atoms are introduced into various metabolic products by these tracers. Detectors record the radioactive radiation emitted by the labeled atoms. Radiologists use the result obtained to diagnose neoplasms and metabolic disorders. The state-of-the-art method of scintigraphy uses the artificial, metastable 99mTechnetium (nuclide generator).The conversion of 99mTc into the 99Tc emits only a soft ß-radiation (beta radiation), which is harmless for the diseased organism. This isotope is particularly popular in radiopharmacy, and 85 percent of radiological examinations are performed using it. 99mTc is obtained by a so-called generator through the use of sterile saline and then eluted. 99m stands for metastable. Subsequently, the conversion into the isotope 99Tc takes place. The patient is injected with a weakly radioactive substance (tracer) in the form of 99-technetium into the arm vein. This is deposited in the areas of the body that are well supplied with blood and metabolically active. After about three hours, the radiologist takes an image of the body provided with the radionuclides. The tracers now tell him in which areas tumors have settled. This is done by a gamma camera, which measures the radiation and shows tumors and other tracer-rich zones as dark spots. Scintigraphy can detect minute metastases that are not visible on a regular X-ray. Tracers are also used in positron emission tomography (PET). The radiation exposure of the radioactively charged particles is low, so that there is no danger to the human organism. Through the PET camera, the tracers make the metabolic processes inside the body visible. In this examination, too, the patient is injected with radioactively labeled substances, for example glucose, into the arm vein so that the radiotracer flows through the body with the blood and settles in the cells there. Tracers are also used in research. They make it possible to elucidate metabolic pathways and their mechanisms and to label substances that participate in metabolism. Researchers use various radiotracers to carry out labeling. The 14C isotope enables age determination. Tritium in the form of the 3H isotope is used to study other metabolic pathways. Isotope labeling changes the chemical properties of the substances only very slightly. For this reason, there is no negative external influence on the metabolic pathway. By using the radionuclides, researchers are able to follow the metabolizations and metabolic pathways without any gaps. Research is currently focusing on the sulfur isotope 35S in the field of tumor diagnostics.
Risks, side effects, and hazards
Regardless of whether tracers are used by giving capsules in internal or metabolic radiotherapy or in diagnostics by positron emission tomography (PET) and scintigraphy, there is no risk to the human organism and thus no additional burden on the general condition. The radiation emitted by the tracers used is comparable to the natural radioactivity to which every human being is exposed. In addition, the body excretes the tracers through the urine after only a short time. In rare cases, they can cause allergies. To be on the safe side, the physician should ask his patient about any allergies before treatment.
