Nuclear Medicine: We’ve Come a Long Way
The days of doctors treating physical ailments with only the use of blood samples and microscopes are long gone, being since replaced or assisted with the use nuclear technology. Nuclear medicine has paved the way to finding the causes for cardiac diseases, cancer, bone problems and other internal ailments that a typical x-ray would not detect. There is now a variety of scans being done, with each having a specific amount of information that can be acquired. Depending on what a doctor suspects an ailment might be determines the type of testing that will be used.
What is Nuclear Medicine?
Like all living organisms, humans are made of biomolecules and are maintained by a kinetic balance called homeostasis. When this balance becomes irregular, due to disease or injury, the body’s molecular system can start to malfunction. Through the technology of nuclear medicine, physicians are able to explore these imbalances and determine the best avenue to begin the healing, when healing is a possibility (Mansi, Ciarmiello, & Cuccurullo, 2012).
Nuclear medicine is different from x-ray, ultrasound and other diagnostic testing in that it uses small amounts of radioactive materials (tracers) that are injected, swallowed or inhaled. The type of tracer used depends on the part of the body that the nuclear imaging devise will be studying. Nuclear medicine can aid in the determination of medical ailments by testing the function of specific organs, tissues, or bone by allowing the physician to visualize the presence of abnormalities due to changes in the appearance of the structure (Iagaru & Quon, 2014a).
Because of technological advances in hybrid imagery and the release of new radiopharmaceuticals (which do not use radioisotopes), nuclear medicine is experiencing continued growth in the United States (US). According to Stanford Medical School physicians, Iagura and Quon (2014a), “continued growth of the field will require cost-effectiveness data and evidence that nuclear medicine procedures affect patients’ outcomes. Nuclear medicine physicians and radiologists will need more training in anatomic and molecular imaging. New educational models are being developed to ensure that future physicians will be adequately prepared.”
Through these advances made in nuclear medicine, the imaging devises available to aid physicians in determining injury and illness have experienced great strides in enabling a more effective diagnosis of illness and injury. Positron emission tomography (PET), bone scintigraphy (bone scan), hybrid imaging such as magnetic resonance imaging (MRI), and white blood cell (WBC) scans are just a few of the technologies available today.
Positron emission tomography (PET)
The most notable application of nuclear imagery is in the cardiology field, with over 1,000 procedures per 100,000 people being performed in the US. The majority of these procedures are taking place in a hospital setting; however, the number of nuclear imaging clinics has seen a substantial rise (Delbeke & Segall, 2011). Positron emission tomography (PET) scans examine the body’s chemistry. Other common medical tests, such as MRI scans and computed tomography (CT) scans, only reveal structural aspects of the body. The advantage of PET scans is their ability to enhance the details about bodily functions. One PET procedure allows physicians to “gather images of function throughout the entire body, uncovering abnormalities that might otherwise go undetected” (Iagura & Quon, 2014a). Because PET scans are a biological imaging examination and disease is a biological process, PET scans are able to detect and stage most cancers sooner than they could be visualized with other common examinations. This early detection also allows physicians access to vital information concerning heart disease and neurological disorders, such as Alzheimer’s. PET scan’s non-invasive, accurate system allows physicians to determine whether a suspected abnormality is malignant or benign, which in turn saves many patients from the need to endure painful and expensive exploratory surgeries, which may not always detect the stage or detriment of a disease. The accuracy of the PET scan aids in earlier detection and diagnosis, putting time on the side of the patient, which increases the chances that treatments will be successful.
While no special preparation is needed prior to a PET scan, some tests require fasting, the elimination of caffeine and a brief cessation of certain medications. Prior to the procedure, the patient is either injected with or given orally a small dose of a radioactive substance, a radiopharmaceutical or tracer, which locates in the specific areas to be tested. This substance emits energy (gamma rays) that are detected with a gamma imaging device, aided by a computer that produces images and measurements of the specified organs or tissue (Iagura & Quon, 2014a).
Bone Scintigraphy (Bone Scan)
Bone scintigraphy (bone scan) is the second most widely used application of nuclear imagery; although, these procedures only account for approximately 17% of nuclear imagery performed in the US (Delbeke & Segall, 2011). Skeletal scintigraphy, when performed correctly, has proven to be an effective method “in detecting anatomic and physiologic abnormalities of the musculoskeletal system”. Different skeletal diseases or injuries, such as accidental and non-accidental trauma, arthritis, bone cancer, and congenital or developmental anomalies, reflect individualized patterns that are observable within the bone scan procedure; therefore, increasing the likelihood of early detection, diagnosis, and treatment (Greenspan, 2013).
Patients receiving a bone scan are asked to stay hydrated before and during testing and are given the smallest possible intravenous dose of a radiopharmaceutical (tracer), usually Technetium-99m or similarly effective compound. General dosing guidelines are followed with dosages for small children and adolescents being based on the patient’s weight. Prior to the scan, which takes place within 2-4 hours of the tracer’s administration, the patient is then asked to empty their bladder, to remove any visual inaccuracy of the scan’s imagery. If the bladder refills during testing the scans will be delayed; although, catheterization may be necessary to avoid interruptions (Greenspan, 2013).
Magnetic Resonance Imaging (MRI)
Unlike PET and Bone scans, MRI scans are noninvasive procedures that do not require radiation to acquire an internal image. MRI’s imaging machinery uses a large magnet and computer to create the internal body images, often referred to a “slices”. These slices display a limited number of body tissue layers at a time. These layers are then examined on the computers monitor, allowing physicians to detect and observe any internal abnormalities. MRI scans can take from 15 to 90 minutes to complete, with an average complete examination taking from 1.5 to 3 hours (Iagura & Quon, 2014b).
Closed MRI machines are large, hollow cylindrical tubes surrounded by a circular magnet. In preparation of an exam, patients receiving an MRI are asked to remove all jewelry, including piercings. Transdermal patches, such as nicotine, birth control, and nitroglycerin patches, (which contain trace amounts of metal) also require removal. Patients suffering from chronic pain or have difficulty lying still may be given mild sedative to facilitate an uninterrupted exam. Prior to any MRI exams, it is important for the patient to inform the physician of any metals that may be in the patient’s body. This includes artificial or prosthetic limbs or joints, bullets or shrapnel fragments, ear implants, pacemakers, IV ports, and any other accidental or intentional metals that might interfere with the exam or harm the patient (Iagura & Quon, 2014b).
White Blood Cell (WBC) Scans
To look for internal infection or inflammation a physician may order a white blood cell (WBC) scan, also known as Leukocyte scans. WBC scan is done to look for a hidden infection. It is particularly useful if your doctor suspects an infection or inflammation in the abdomen or bones, like those that may be experienced after a surgery. WBC scans are nuclear imaging scans that use radiopharmaceuticals (tracers) to look for infection or inflammation in the body. In a procedure referred to as tagging, blood is taken from a patient’s vein, the white blood cells are separated from the sample, mixed with a fractional amount of radioactive material (radioisotope, referred to as indium-111), then returned to the patient’s blood stream, 2-3 hours later, via an intravenous injection. The patient’s body undergoes the scan 6-24 hours later. The scanning machine, which resembles as x-ray device, detects the radiation emitted from the tagged white blood cells and a computer then displays the image created by radiated blood cells (Dugdale, 2012).
WBC scans take 1 to 2 hours to complete and usually take place in a hospital setting; however, outpatient clinics are also available. While there are no special necessary preparations, much like an MRI, patients are required to remove all jewelry, piercings, and other metal containing objects, including hearing aids and denture apparatus containing metal. Patients are asked to wear loose fitting clothing (without metal snaps or zippers) or don a hospital gown. Your physician will need to be told if during the previous month, you have undergone a gallium scan, are receiving dialysis, receive nutrition through an IV or steroid therapy, have hyperglycemia, or are taking long-term antibiotics; as patients may be asked to discontinue the use of antibiotics prior to the test. WBC scans are not recommended for women who are pregnant or if trying to become pregnant, birth control is recommended during the course of WBC procedures (Dugdale, 2012).
Radiopharmaceuticals involve small amounts of radioactive materials (tracers) that are injected, swallowed or inhaled, with the type of tracer used depending on the part of the body that the nuclear imaging devise will be studying. Radiopharmaceuticals (not using radioisotopes), like Technetium-99m (Tc-99m), account for about 50,000 medical imaging procedures daily in the United States. Tc-99m is the most routinely used medical isotope today Tc-99m is derived from the parent isotope Mo-99, predominantly produced from the fission of uranium-235 in highly enriched uranium targets (HEU) in aging foreign reactors. North America’s supply of Tc-99m was heavily disrupted after Canada’s Chalk River nuclear reactor experienced an outage several years ago (Ambrosiano, 2013).
In an effort to reduce supply interruptions and eliminate the “potential use in nuclear weapons, acts of nuclear terrorism, or other malevolent purposes” (White House, 2012), the Los Alamos National Laboratory announced that “for the first time, irradiated low-enriched uranium (LEU) fuel has been recycled and reused for molybdenum-99 (Mo-99) production, with virtually no losses in Mo-99 yields or uranium recovery”. This further demonstrates the feasibility of the separation process and the probability of environmentally, cost-friendly fuel recycling (Ambrosiano, 2013).
Advantages, Disadvantages, and Safety
The obvious advantages of nuclear medicine are realized in the number of patients who are surviving cancer, managing Alzheimer’s and Parkinson’s, and overcoming serious bone injuries. Nuclear imaging has become an irreplaceable tool in determining the reduction or recurrence of cancers, making its use as important as any of the medications used in a patient’s treatment. Because only one scan is needed to obtain a full body representation, repeated testing is often unnecessary, proving these procedures to be more cost effective as well (Iagura and Quon, 2014).
The medical disadvantages of nuclear imaging are more apparent with individual patients and the inability to apply the technology to all patients. Certain physical factors limit the use of MRI imaging when the patient has imbedded and internal metals, i.e. pacemakers, surgically implanted feeding tubes, pins, rods and other permanent metals. MRIs are also not recommended for pregnant patients prior to 3 months into pregnancy. Pregnancy is also a factor in potential use of PET and WBC scans as the possible dangers during pregnancy are yet to be determined (Iagura & Quon, 2014b).
Economically, nuclear imaging is expensive and many insurance companies limit its use without verifiable need is determines; thus leaving some patients with decreased levels of treatment or no treatment at all. Another factor is due to limited access to reliable sources of the isotopes needed to perform the imaging. The US is addressing this issue with accelerated commercial projects to produce the molybdenum-99 isotope domestically, reducing the use of highly enriched uranium (HEU) and increasing the use of low-enriched uranium (LEU), like the advancements being made at the Los Alamos National Laboratory (White House, 2012 & Ambrosiano, 2013).
Nuclear imaging procedures are considered the safest, most prevalent imaging exams being used today. Patients receive radiopharmaceuticals in minimal doses that deliver the smallest amount possible to achieve the diagnostic information needed; often exposing the patient to less radiation than an x-ray (Greenspan, 2013). The scanning device does not produce any radiation and the radiation emitted from the radioisotopes is minimal; as the materials breaking down quite rapidly, all small traces of radioactivity have generally diminished in 1 or 2 days. There are no verifiable cases of injury due exposure to radioisotopes (Dugdale, 2012). The education and training received by radiologists, technologists, and physicians requires responsible behavior that ensures the safety of the staff and patient alike. In order to produce the quality image required for diagnostic success an “as low as reasonably achievable” (ALARA) approach is maintained to ensure minimal dosages and exposure (Greenspan, 2013).
Nuclear medicine and medical imaging has come a long way and regardless of the continuing hurdles the advancements already gained allow physicians of today and those of the future to pursue new avenues in prevention, diagnosis and healing of the many ailments that patients and physicians face together. PET, MRI, WCB, and improving radiopharmaceuticals are improving and saving lives every day. Future discoveries and continued research will aid in finding the causes for cardiac diseases, cancer, bone problems and other internal ailments that in the past could lead to continued illness and premature death. While there is still a long way to go, a future free from disease, illness and permanent injury is no longer so far away.
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White House. (2012). Fact sheet: Encouraging reliable supplies of molybdenum-99 produced without highly enriched uranium. Office of the Press Secretary. Retrieved from http://www.whitehouse.gov/the-press-office/2012/06/07/fact-sheet-encouraging-reliable-supplies-molybdenum-99-produced-without-