In vivo diagnostic agents are medical tools that help physicians diagnose diseases in living humans. The best-known in vivo diagnostic agents include iodine-based contrast agents for informative imaging procedures and radioisotopes for diagnostic scintigraphy procedures. Because in vivo diagnostic agents are also administered to healthy people, they may involve only minor risks and side effects.
What are in vivo diagnostic agents?
In vivo diagnostics are defined by physicians as all tools used for the purpose of medical diagnosis on living patients. For example, this includes all imaging procedures that are made possible in the first place via contrast media or other substances. By in vivo diagnostics, the physician understands all aids for the purpose of medical diagnosis on living patients. These include, for example, the aids used in imaging procedures such as computer tomography. In this context, in vivo diagnostics encompasses all imaging procedures that are made possible by contrast media or other substances. The contrast medium used in X-rays, ultrasound examinations, MRI or CT is therefore one of many different in vivo diagnostic agents. The term in vitro diagnostics must be distinguished from this. In contrast to in vivo procedures, in vitro procedures do not take place on living humans. Instead, in an in vitro procedure, the physician removes body fluids or tissue from the patient. These removed samples are examined in the laboratory for diagnostic purposes. The medical devices used for this purpose are called in vitro diagnostic devices.
Function, effect, and objectives
Both in vitro, and in vivo diagnostic devices are intended to help the physician diagnose or rule out a disease. In live patient imaging procedures, for example, the contrast agent is used to provide more differentiated images of anatomic structures. The contrast agent is usually given intravenously before and during imaging. Intravenous contrast agent administration is used, for example, for well-differentiated imaging of the spine. Intravenous administration allows vessels to be identified and diseased tissue structures to be distinguished from healthy tissue structures. Rectal administration of contrast media, on the other hand, is used for imaging of the colon or lower abdomen. This allows delineation of the lower abdominal organs from the intestinal loops. In turn, oral administration of contrast agents allows better separation of the stomach and intestine from other organs. In addition to iodine-containing contrast media, modern medicine works primarily with barium sulfate-containing suspensions. The iodine-containing solutions are currently the most commonly used and are mainly used for imaging veins, kidneys or organs. Agents containing barium sulfate are used in particular for imaging the esophagus or gastrointestinal tract. In vivo diagnostic agents such as the contrast agent thus improve the informative value and reliability of imaging at any location in the body. A similar situation applies to radioisotopes, which can also be described as in vivo diagnostic agents. These radioisotopes include, above all, fluorodeoxyglucose and 99-technetium. Both substances are used in scintigraphy or in PET and SPECT. As a rule, these substances are injected. The substances are radioactively labeled in vivo diagnostic agents. For the nuclear medicine imaging procedures mentioned, the physician introduces them into the patient’s body. In scintigraphy, a gamma camera measures the radiation emitted by the deposited in vivo diagnostic agents. PET and SPECT show a cross-sectional image similar to MRI. Both methods make biochemical and physiological functions visible with the help of the radioactively labeled in vivo diagnostics. Radioisotopes play a particularly important role in cancer diagnostics. While they are in vivo diagnostics in this context, they are no longer diagnostic tools in actual cancer therapy. Rather, they become the actual focus of therapy in cancer treatment. For example, radioisotopes given in a targeted manner are intended to shatter tumors. In the future, in vivo diagnostics will be guided by nanotechnology. For example, nanoparticulate contrast agents, with their deposition in diseased cells, are expected to enable early detection of various diseases in the future.
Risks, side effects and dangers
A special feature of in vivo diagnostics is the legal basis.As long as the aids do not have an immunological, pharmacological or metabolic effect, they are considered medical devices and are subject to the legal regulations within this framework. However, as soon as in vivo diagnostics exert a physical effect, they already belong to the category of medicinal products instead of medical devices. This means that they are subject to the laws on medicinal products instead of medical devices. As a rule, in vivo diagnostics are used before the actual assessment of patient health or are even applied to completely healthy patients. In this context, medical devices are subject to completely different requirements in terms of risks and side effects than a drug. Drugs are administered to sick patients. Risks and side effects are therefore tolerable to a high degree, depending on the disease and the benefit of the drug. This benefit/risk ratio does not apply to in vivo diagnostics. Side effects are therefore only accepted to a limited extent in connection with in vivo diagnostics. With regard to diagnostics such as contrast media, this was not always the case. For example, toxic contrast media were still used in the past, some of which later caused liver tumors. Today’s contrast media, on the other hand, are well tolerated. Apart from a metallic taste and headache reactions, the administration is usually associated with only minor risks and side effects. In rare cases, allergic reactions such as itching, rash or shortness of breath occur. Under certain circumstances, regulatory disorders of the thyroid gland may occur. In the case of radioisotopes, the degradability and the decay rate of the radioactively labeled substances play a major role. The radioisotopes used today are usually extremely short-lived. In particular, the frequently used 99-technetium has proven to be relatively well tolerated. Side effects include fatigue in some cases. Shortness of breath and general weakness are also among the most notable side effects.
