In this process, one of the neutrons in the nucleus is converted into a proton and the excess energy is released in the form of a pair of particles, an electron and an antineutrino (ν). As soon as an electron from the K, L or M shell is captured, a vacancy is created in the inner shell of the atom.
Detection Of Radiation
The kidney cells concentrate 99m-DMSA and imaging of the kidney can show the distribution of the tracer in this organ. This instrument works on the principle that when radiation passes through air or a specific gas, the molecules in the air are ionized. When a high voltage is placed between two regions of the gas-filled space, the positive ions will be attracted to the negative side of the detector (cathode) and the free electrons will travel to the positive side (anode).
The first part of the photomultiplier tube is made of another special material called a photocathode. The sequence continues until the last dynode is reached, where the electron pulse is now millions of times larger than it was at the beginning of the tube. At this point, the electrons are collected by an anode at the end of the tube, forming an electronic pulse.
Radiopharmaceuticals
The goal of radionuclide therapy is complete ablation of the target with minimal radiation exposure to surrounding structure. As the half-life of the radionuclide increases, the cumulative radiation dose to the target tissue increases, resulting in better ablation. 99mTc phytate uptake in spleen is minimal and most of the tracer goes to liver.
This mechanism uses the normal function of the spleen, which recognizes and blocks damaged erythrocytes. The structural configuration of the molecule is more important than the presence of the specific atom in the molecule eg. Antigenic diversity of tumors, insufficient dose delivered to the target region are some of the limiting factors in the widespread use of monoclonal antibodies.
Production of radionuclides
In-111 Oncoscint (anti-CEA antibody) is useful in the detection of recurrence of colorectal cancers. In the presence of rising CEA levels after surgery with normal CT/MR studies, the examination is useful in identifying the source of the rise in CEA. The parent nuclide is stored in a suitable container, known as a generator, and can be transported to a distant location.
In the above example, the parent has a long life from which a daughter with a shorter half-life can be periodically separated. The shorter half-life allows the administration of a larger dose to the patient without unnecessarily increasing his exposure to radiation and making it easier to detect this radioactivity in the body. Apart from that, the main advantage of these compounds lies in their constant availability in the laboratory.
In Vitro Assays
The radioactive element resulting from the unstable state of the nucleus begins to dissociate into a daughter product, which is also radioactive, and in turn disintegrates into another element, which is stable. Daughter nuclide can be easily separated from its parent on site in hospitals and central radiopharmacies and used for various imaging purposes. The hormone concentration in unknown plasma is determined by the degree of binding of the labeled hormone in the sample by comparison with the binding observed with standard solutions containing known amounts of hormone.
The basic principle of the radioimmunoassay is also called competitive inhibition, where there is real competition between the immunoreactivity of the hormone in the standard and the unknown serum for the antibodies added for the reaction. There are countless substances that can be evaluated by radioimmunoassays, e.g. various peptide hormones, drugs, nutrients, steroids, infectious agents. Growth hormone, TSH, thyroxine, insulin, FSH, and LH can be readily assayed by these techniques, and interesting new physiological data have emerged as a result of the widespread use of these assays.
Study of intermediary metabolism
Autoradiography
Positron Emission Tomography (PET)
Scintigraphy and Imaging of Organs
If the radiopharmaceutical used is such that it localizes to the normally functioning cells of an organ, such a defect would be seen as a void, conventionally described as a 'cold zone'. If the radiopharmaceutical is localized only in the pathological lesion, the image shows the lesion as positive or 'hot zone'. Colloidal preparations of 99 mTc, such as sulfur-colloid or phytate, are localized in the RES cells of the liver.
Red blood cells labeled with radioactive chromium (51Cr) or 99mTc and then denatured by heat tend to localize in the spleen. Macroaggregated albumins are large particles and are retained in the capillaries of the lungs after an intravenous injection. Glucose or 11C- or 18F-labeled amines, radioiodine-labeled amphetamine, and several other chemicals cross the blood-brain barrier to localize in the brain substance.
It is one of the fastest and most non-invasive methods for finding metastatic spread in the skeleton of a patient's primary cancer. One group of studies deals with the localization of the appropriate radiopharmaceutical in normal myocardium, e.g.
Dynamic Function Studies
Plasma volume. Radioiodine labeled albumin remains in the plasma compartment of the blood and the degree of its dilution allows determination of plasma volume
Total exchangeable sodium and potassium. This is determined by using radioactive sodium and potassium as tracers
Total body water. Administration of radioactive water permits the estimation of total body water
The percentage of the administered dose that accumulates in the gland at different times can be determined. The fate of a radioactive tracer after its introduction into the body can be followed to obtain useful physiological information. Later, how much and the rate at which the same tracer reappears in the RBC can be determined.
If the same study continues, it will be possible to observe the fate of these endogenously labeled erythrocytes. It can be carried out using two methods: the first pass method and the squeeze ratio method. a) The passage of the radioactive bolus is studied through the different chambers of the heart using a gamma camera connected to a digital computer. Images of the heart can be collected at specific times during the cardiac cycle by triggering the gamma camera via an electronic signal from the E.C.G.
Absorption Studies
In the above type of studies, the fate of a radioactive tracer is involved. If the tracer is such that it is confined to the vascular compartment and remains in the circulation, then it can provide information about the speed of blood flow through several organs. The study of cardiac output consists of introducing a radioactive bolus and detecting its passage by an external detector over the precordium.
It can show shunts by abnormal patterns of time-activity histograms for passage through each of the heart chambers. This type of single-pass study can also estimate the left ventricular ejection fraction by measuring the variation in radioactivity across the left ventricle between systole and diastole. Estimation of change in left ventricular volume during systole and diastole allows the measurement of left ventricular ejection fraction.
Therapeutic Applications of Radioisotopes
The images of the heart can be collected at specific times during the cardiac cycle by activating the gamma camera via an electronic signal from E.C.G. By estimating the change in left ventricular volume during systole and diastole, left ventricular ejection fraction can be measured. In contrast to external radiotherapy, radiotherapy delivered via internal administration of radionuclides targeted via a tumor-seeking carrier has the appeal of the “magic bullet”. A large amount of radioactive iodine concentrates specifically in the thyroid gland and therefore it is possible to deliver a large, ablative dose to the thyroid gland without affecting other parts of the body.
Calculation of the dose required to achieve this is complicated and difficult, as it has to take into account several continuous factors such as the size of the thyroid gland, biological half-life of radioiodine in the thyroid gland, uptake of radioiodine by the thyroid gland, etc. variety of radionuclides, such as 131I, 188Re, 90Y can be used for this purpose and the targeting of the therapeutic agent to the tumor can be achieved by either direct intratumoral implantation of radionuclides or by injecting radionuclide through the hepatic artery directly into the tumor (transarterial radionuclides) therapy or TART) or by parenteral injection of radiolabeled antibodies specific for HCC antigens. Although they do not affect the course of the disease, pain is significantly reduced and patients become mobile.
Biological Hazards Of Radiation
Any biological effect of radiation, harmful or benign, is highly dependent on the radiation dose. With stochastic effects, the chance of occurrence and not the severity of the effect depends on the radiation dose. In deterministic effects, on the other hand, the severity of the effect depends on the radiation dose and has a threshold value, a dose below which no effect is observed.
Given the same radiation dose and dose rate, bone marrow is much more sensitive than nerve tissue to certain types of radiation damage. v) Amount of tissue. These are usually produced when the radiation dose is high and is distributed over a large part of the body in a short duration. Late effects can occur in cases where the radiation dose to the whole body is low or only a part of the body is involved in the radiation.
Safety Measures in Handling Radioisotopes
Five clinically distinct stages can be distinguished as the radiation dose is gradually increased: no effect, mild damage to the bone marrow, severe damage to the bone marrow and mild damage to the gastrointestinal tract, severe damage to the gastrointestinal tract and damage to the central nervous system. system. In diagnostic uses of radiation, both in radiology and nuclear medicine, the range of radiation doses typically administered to a patient falls into this category. Unfortunately, it is difficult to obtain accurate information about the risks associated with low radiation doses for the following reasons.
Second, the appearance of a latent period in the expression of late effects requires a long follow-up (10 years or more). Finally, late effects of radiation also occur naturally and more frequently than those caused by low doses of radiation. Because accurate information about the natural frequency of these effects is lacking, it is difficult to estimate the influence (increase or decrease) of low radiation doses.
Conclusion
