The most commonly used gaseous/aerosol radio nuclides are:
A colorless, heavy, odorless noble gas, xenon occurs in the earth's atmosphere in trace amounts. Although generally unreactive, xenon can undergo a few chemical reactions such as the formation of xenon hexafluoroplatinate, the first noble gas compound to be synthesized.
Gamma emission from the radioisotope 133Xe of xenon can be used to image the heart, lungs, and brain, for example, by means of single photon emission computed tomography. 133Xe has also been used to measure blood flow.
Because the nucleus of the isotope 129Xe has an intrinsic angular momentum of spin ½, when it is placed in the presence of an alkali vapor this nucleus can be readily polarized using light from a circularly polarized laser. Typically the alkali metal rubidium is used for this purpose. The polarization can approach 50% of all the xenon atoms, a condition called hyper polarization. As xenon's electron shell is symmetric, there is only a minimal coupling between the polarized nucleus and external magnetic fields, so the hyperpolarized state can be conveniently maintained for a period of several days. The hyper polarization process renders the xenon more detectable via magnetic resonance imaging and has been used for studies of the lungs and other tissues. It can be used, for example, to trace the flow of gases within the lungs.
A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other rare gases in fluorescent lamps. Krypton is inert for most practical purposes but it is known to form compounds with fluorine. Krypton can also form clathrates with water when atoms of it are trapped in a lattice of the water molecules.
81Kr, the product of atmospheric reactions is produced with the other naturally occurring isotopes of krypton. Being radioactive it has a half-life of 250,000 years. Krypton is highly volatile when it is near surface waters but 81Kr has been used for dating old (50,000 - 800,000 year) groundwater.
Technegas was the name coined in November 1984 to describe what we now know to be a specialized sub-set of nano-encapsulated carbon composites. Technegas, as produced in a purpose-built apparatus for lung ventilation work, consists of hexagonal flat crystals of Technetium metal cocooned in multiple layers of graphite sheets completely isolating the metal from the external environment.
A commercial apparatus was developed in conjunction with a small engineering firm in Sydney, Australia, and the first machines sold locally in 1986. Now about 1000 machines are in use in 43 countries where about 200,000 diagnostic examinations are performed each year. It is estimated from sales of consumables that 2,000,000 patients will have been studied with Technegas by October 2007 without a single report of adverse events.
Technetium-99m-DTPA is primarily used for renal imaging and for measuring glomerular filtration rate. After intravenous injection it is excreted entirely by glomerular filtration. Technetium-99m-DTPA is used for renal imaging because it has rapid elimination by filtration. Early images of the kidney allow good demonstration of the parenchyma because of the blood supply in the kidney.
Preparations for Nuclear Medicine Procedures
Usually, no special preparation is needed for a nuclear medicine examination. However, if the procedure involves evaluation of the stomach, you may have to skip a meal before the test. If the procedure involves evaluation of the kidneys, you may need to drink plenty of water before the test.
Some minor discomfort during a nuclear medicine procedure may arise from the intravenous injection, usually done with a small needle. With some special studies, a catheter may be placed into the bladder, which may cause temporary discomfort. Lying still on the examining table may be uncomfortable for some patients.
Most of the radioactivity passes out of your body in urine or stool. The rest simply disappears through natural loss of radioactivity over time.
Nuclear Medicine Procedures Administration
You are given a small dose of radioactive material, usually intravenously but sometimes orally, that localizes in specific body organ systems. This compound, called a radiopharmaceutical agent or tracer, eventually collects in the organ and gives off energy as gamma rays. The gamma camera detects the rays and works with a computer to produce images and measurements of organs and tissues.
A radiopharmaceutical agent is usually administered into a vein. Depending on which type of scan is being performed, the imaging will be done either immediately, a few hours later, or even several days after the injection. Imaging time varies, generally ranging from 20 to 45 minutes.
The radio pharmaceutical that is used is determined by what part of the body is under study, since some compounds collect in specific organs better than others. Depending on the type of scan, it may take several seconds to several days for the substance to travel through the body and accumulate in the organ under study, thus the wide range in scanning times.
While the images are being obtained, you must remain as still as possible. This is especially true when a series of images is obtained to show how an organ functions over time.
After the procedure, a physician with specialized training in nuclear medicine checks the quality of the images to ensure that an optimal diagnostic study has been performed.
Most patients undergo a nuclear medicine examination because their primary care physician has recommended it. A physician who has specialized training in nuclear medicine will interpret the images and forward a report to your physician. It usually takes a day or so to interpret, report and deliver the results.
A patient undergoing a nuclear medicine procedure will receive a radiation dose. Under present international guidelines it is assumed that any radiation dose, however small, presents a risk. The radiation doses delivered to a patient in a nuclear medicine investigation present a very small risk of inducing cancer. In this respect it is similar to the risk from X-ray investigations except that the dose is delivered internally rather than externally.
The radiation dose from a nuclear medicine investigation is expressed as an effective dose with units of sieverts (usually given in millisieverts, mSv). The effective dose resulting from an investigation is influenced by the amount of radioactivity administered in megabecquerels (MBq), the physical properties of the radiopharmaceutical used, its distribution in the body and its rate of clearance from the body.
Effective doses can range from 6 μSv (0.006 mSv) for a 3 MBq chromium-51 EDTA measurement of glomerular filtration rate to 37 mSv for a 150 MBq thallium-201 non-specific tumour imaging procedure. The common bone scan with 600 MBq of technetium-99m-MDP has an effective dose of 3 mSv (1).
Diagnostic tests in nuclear medicine exploit the way that the body handles substances differently when there is disease or pathology present. The radionuclide introduced into the body is often chemically bound to a complex that acts characteristically within the body; this is commonly known as a tracer. In the presence of disease, a tracer will often be distributed around the body and/or processed differently. For example, the ligand methylene-diphosphonate (MDP) can be preferentially taken up by bone. By chemically attaching technetium-99m to MDP, radioactivity can be transported and attached to bone via the hydroxyapatite for imaging.
Any increased physiological function, such as due to a fracture in the bone, will usually mean increased concentration of the tracer. This often results in the appearance of a 'hot-spot’, which is a focal increase in radio-accumulation, or a general increase in radio-accumulation throughout the physiological system. Some disease processes result in the exclusion of a tracer, resulting in the appearance of a 'cold-spot'. Many tracer complexes have been developed in order to image or treat many different organs, glands And physiological processes. Tests can be divided into the two broad groups: in-vivo and in-vitro:
Compared to traditional diagnostic methods, nuclear cardiology testing dramatically reduces the time it takes to detect a heart attack or unstable angina. Strong Health’s two nuclear cardiology laboratories, at Clinton Crossings and the Paul N.Yu Heart Center at Strong Memorial Hospital, offer complete stress testing capabilities for outpatients, as well as Strong Memorial Hospital inpatients and ER patients. Strong Health’s high-performance multi-head gamma cameras produce 3-D, computer-reconstructed images of the heart. Multiple views enable the team to assess cardiac function and regional cardiac blood flow.
Nuclear Cardiology Test
Like a stress echo test, nuclear cardiology studies produce images of the heart at work and at rest. During a test, you are given an injection of a small dose of a harmless radioactive tracer. Then you spend time exercising on a treadmill or stationary bicycle and then resting. A specialized camera called a "gamma camera” detects the tracer as it passes through the chambers of your heart, creating the pictures. The pictures may reveal problems in heart muscle and blood vessels, especially when the images of the heart at work and at rest are compared. The main type of nuclear cardiology test is called a Ventricular Function Test.
Ventricular Function Test
This test is primarily designed to study how well the heart is pumping, how much blood it pumps per beat, etc. The test can also visualize the integrity of the cardiac chambers and valves and also monitor the effect of different drugs on the heart muscle such as chemotherapy drugs.
There are two types of tests:
MUGA study is more common than the Angiography First Pass Study.
Nuclear chemistry deals with radioactivity, nuclear processes and nuclear properties. It is the chemistry of radioactive elements such as the actinides, radium and radon together with the chemistry associated with equipment (such as nuclear reactors), which are designed to perform nuclear processes. This includes the corrosion of surfaces and the behaviour under conditions of both normal and abnormal operation (such as during an accident). An important area is the behaviour of objects and materials after being placed into a waste store or otherwise disposed of. The radiation chemistry controls much of radiation biology as radiation has an effect on living things at the molecular scale, to explain it another way the radiation alters the biochemicals within an organism, the alteration of the biomolecules then changes the chemistry which occurs within the organism, this change in biochemistry then can lead to a biological outcome. As a result nuclear chemistry greatly assists the understanding of medical treatments and has enabled these treatments to improve.
Contribution of chemistry to medicine
Drugs are chemicals - all medicines are made or refined by chemical processes. Eg painkillers, anti-biotics, anti-cancer drugs etc
Many diseases have their root cause at a metabolic level - the understanding of the chemical reactions that take place assist in understanding and treating the disease.
Genetic diseases can be screened by DNA analysis - a chemical process
Aneasthetics are chemicals
Benefits and Risks of Nuclear Medicine
Unlike other imaging technologies that diagnose disease based on anatomy or structural appearance, nuclear medicine determines the cause of a medical problem based on organ function. Nuclear medicine procedures can be digitally combined with computed tomography (CT) scans or magnetic resonance imaging (MRI) studies to give the most complete picture of the tissues or lesions being evaluated.
Nuclear Medicine Week
Every year, the Society of Nuclear Medicine and the Society of Nuclear Medicine Technology join forces with the nuclear medicine and molecular imaging community to gain recognition and support for the field. Celebrated during the first full week of October, Nuclear Medicine Week encourages community members to take pride in their profession – recognizing their colleagues for their hard work and promoting nuclear medicine to the entire medical community as well as to the public.
Nuclear Medicine helps with cancer detection and treatment
Innovative use of somatostatin receptor scintigraphy (SRS), a nuclear medicine imaging technique looking at how the body functions at the molecular level, may provide near immediate selection of breast cancer patients for endocrine therapy and offers a new tool in fighting the disease.
Breast cancer is the most common cancer among women and the second leading cause of cancer death. About one in eight women will develop invasive breast cancer some time during her life, and more than 40,000 (1 in 33) of those die from the disease each year. Advanced or metastatic breast cancer patients receive either hormonal or chemotherapy treatment, depending on the hormone sensitivity of a woman's tumor. In some women, the female hormone estrogen promotes the growth of breast cancer cells. Endocrine or hormonal therapy removes the influence of estrogen on breast cancer cells, preventing the cancer cells from growing and spreading.
The only technique used now to determine whether a patient's tumor is sensitive to hormonal therapy is examination of a piece of tumor tissue in a lab to see if hormone receptors are present. With nuclear medicine, it is possible to take an imaging scan of the entire patient--and treatment should be started when metastasis occurs--to evaluate if the tumor lesions are hormone sensitive and to assess what treatment would be efficient.
Non-Hodgkin’s lymphoma is a cancer of the lymphatic system, the body’s blood-filtering tissues that help to fight infection and disease. A variety of factors including congenital and acquired immunodeficiency states—as well as infectious, physical and chemical agents—have been associated with an increased risk of developing non-Hodgkin’s lymphoma. This cancer of the immune system became more familiar to the general public as it struck celebrities such as Jackie Kennedy Onassis, baseball great Roger Maris and King Hussein of Jordan.
Nuclear medicine has a growing role in treating non-Hodgkin’s lymphoma. When nuclear medicine is used earlier in the course of the illness, there is a higher efficacy of treatment.
Patients who had been previously treated with and had failed to respond or responded poorly to multiple types of chemotherapy—and whose tumors had recurred—received a single course of treatment with a radioactive antibody or “smart drug” injected into the bloodstream that targets and kills cancer cells. Of those patients, 65 percent responded to treatment; 20 percent had complete response or no evidence of remaining cancer. Four years later, the update revealed that those patients who achieved a complete response had “an enduring response,” indicating that while we can’t say the patients are ‘cured,’ they have lived without the disease recurring for a substantial period of their lives.
With the therapeutic regimen, a patient receives an injected test dose of the antitumor monoclonal antibody— tositumomab and iodine I-131 tositumomab—to determine how his or her body processes that tagged antibody. Nuclear medicine imaging scans assess how quickly the drug reaches the tumor and how quickly radiation disappears from a patient’s body. The dose given to each patient is individualized to the patient’s own handling of the drug, so the patient receives a “personalized dose” of the treatment. Therapy is considered complete after the patient receives that individualized therapeutic dose, typically one week or so after the dosimetric dose.
The current standard course of treatment for lymphoma is intensive chemotherapy. Patients receive chemotherapy every three weeks over a time period of up to six months. This treatment has unpleasant side effects, including nausea, hair loss and infections. With the nuclear medicine treatment, patients find that the most common side effect is a temporary lowering of blood counts for several weeks. Patients are now offered a choice of months of chemotherapy or a tracer and treatment dose given over about a week.
Results are even more promising using tositumomab and iodine-131 tositumomab earlier in the course of the illness before much chemotherapy have failed.
The current role and future
The current role of nuclear medicine in clinical diagnosis was surveyed in a retrospective review of medical records by two internists. About one radio logic imaging study in 20 was a radionuclide procedure, and a somewhat larger fraction was performed in outpatients.
The internists found that diagnostic-screening procedures in nuclear medicine influenced patient management in 63% of hospital inpatients And quantitative/monitoring types of tests influenced management in 56%. Of the projected health care costs in the United States of $490 billion, all imaging procedures will account for only $12 billion And nuclear medicine procedures will account for about $1 billion. Nuclear medicine research continues to blossom.
Two major problems may hinder the future practice of nuclear medicine in the United States compared with that in other developed countries:
The recent developments which will probably induce the greatest changes in clinical nuclear medicine in the near future are the improvements in design and utilization of single photon emission computed tomographic devices and prolific generation of new radio pharmaceuticals, especially technetium-99m agents for cerebral and myocardial imaging and tumor agents.