FAQ nuclear medicine

The patient receives information about the examination procedure from the nuclear medicine staff. Patients might feel stressed and fearful about the procedure, often due to inaccurate information from non-experts. Therefore, it is essential that patients are provided with accurate and clear information about the basic principles of the procedure when considering a nuclear medicine examination.

Once a patient is scheduled for a nuclear medicine examination, they will receive information sheets detailing the procedure. Additionally, the medical team and nursing staff should provide explanation and clarification of the examination procedure. In some cases, it may be helpful to ask the nuclear medicine staff to speak directly with the patient.

Most examinations require little or no preparation from the patient. However, for some procedures, it is important that the patient has had enough to drink. Such examinations should not be conducted on a day when oral intake is not allowed for the patient (e.g., due to other planned examinations).

For PET examinations using [18F]FDG, it is generally necessary that the tracer is administered while the patient is fasting with a normal blood sugar level. Therefore, patients must fast for at least 5 hours and can only have sugar-free drinks or infusions for hydration.

Iodine, used as a contrast agent in conventional radiological examinations, can block the uptake of the radionuclide in thyroid examinations. If possible, a thyroid scintigraphy should be performed before any examination involving contrast agents. Failure to observe this may result in having to postpone a thyroid scintigraphy for up to eight weeks after the administration of a contrast agent.

The principle of radiation protection requires that every exposure to radiation be kept as high as necessary and as low as possible. Consequently, it is necessary to know the radiation dose resulting from a nuclear medicine examination for the patient. This dose can be compared with those from other possible procedures. Additionally, it is desirable to understand the health risks associated with the radiation exposure.

Patients who are scheduled for a nuclear medicine examination are naturally concerned about the use of radioactive substances within their bodies. This is especially true for pregnant women, those who might be pregnant, and breastfeeding mothers. Even if the doctor deems the examination necessary after considering all options, it is essential to present the risks of such an examination to the patient in a way that they can understand.

For example, the risk can be compared to smoking a few cigarettes or traveling a certain distance by car or plane. The radiation exposure is measured as "effective dose" and given in millisieverts (mSv). For the majority of diagnostic examinations, the dose is under 5 mSv, and often under 1 mSv.

The information about the radiation dose of individual examinations should be understood as approximate values: The individual dose depends on various factors, such as the administered activity, the patient’s anatomy, and the specific organ function.

For comparison: The natural radiation exposure in Austria is about 2–3 mSv per year. This is an average value that varies depending on a person's location. The statistical risk of causing a fatal cancer with a dose of 1 mSv is 50 in 1 million (0.005%).

For individuals still capable of reproduction, this risk is a quarter of that value for subsequent generations. To put this risk into perspective, the risk of death due to anesthesia during surgery is 40 in 1 million (0.004%).

The risk of a fatal traffic accident is 200 in 1 million (0.02%) for a yearly mileage of about 15,000 km. Smoking just one cigarette a day over a period of 10 years results in 2,500 deaths per 1 million smokers (0.25%). And, from the age of 55, the risk of dying from any cause is 10,000 per 1 million people (1%). Table 1 shows these risks in relation to a radiation dose of 1 mSv.

Risks Compared to a Radiation Dose of 1 mSv:

• 1 mSv = 200 km of motorcycle riding
• 1 mSv = 3,750 km of driving a car
• 1 mSv = 18,000 km of flying
• 1 mSv = 75 cigarettes of smoking
• 1 mSv = 75 minutes of climbing
• 1 mSv = 1–2 years of working in a factory
• 1 mSv = 17 hours of living as a 60-year-old

Recently, a more understandable risk assessment has been attempted by calculating the loss of life expectancy due to diseases, accidents, socioeconomic factors, and other factors. This type of risk estimation is easier to understand compared to the previous figures.

A single exposure of 1 mSv would theoretically result in a loss of life expectancy of 0.3 days, while an exposure of 10 mSv would result in a loss of 1.5–3 days. This is much lower than the loss of life expectancy due to diseases or self-inflicted measures such as alcoholism, smoking, or obesity. For example, half a kilogram of excess weight is associated with a theoretical loss of life expectancy of one month. These observations highlight that radiation exposure in the typical range of most nuclear medicine examinations (1–5 mSv) poses a theoretical risk that is negligibly small. Furthermore, no adverse effects have been reported from patient examinations using nuclear medicine methods, even considering studies involving children.

Pregnancy

If necessary, some nuclear medicine examinations can be performed on pregnant women, such as a lung scan to diagnose or rule out a pulmonary embolism. Pregnancy is not an absolute contraindication for a nuclear medicine examination. However, the well-being of the developing child must always be considered. Therefore, the risks and benefits must be weighed as carefully as possible, and the woman must be thoroughly informed.

Routine examinations are not conducted on pregnant women unless the results are urgently needed for current treatment and cannot be postponed until after the pregnancy. The dose to which a fetus is exposed varies greatly depending on the type of examination and can be minimized for pregnant women by reducing the administered activity.

The principal risk for the fetus is considered to be the potential development of cancer in childhood. Estimates of this risk range from 30 to 130 cases per 1 mSv. There is no evidence of congenital malformations in a fetus exposed to less than 100 mSv. The possibility of developmental delay is currently considered to be a reduction in IQ by 0.03 points per mSv if the exposure occurs during the gestational period of 8 to 15 weeks.

In simple terms, no detectable effects have been observed from any nuclear medicine examination. No harm is seen to the live-born child from exposure of an embryo during the first three weeks after conception.

The consideration of a nuclear medicine examination for a pregnant woman should be discussed with the head of the relevant department or a responsible physician in consultation with a nuclear medicine specialist. It is crucial that a pregnant or breastfeeding woman receives an explanation of the risks associated with such an examination before coming in for the procedure.

Pregnancy and the postpartum period are emotionally demanding, and radiation exposure during pregnancy often raises significant concerns. A patient in this situation may seek advice from her partner, and there may not be time for this if she is only informed of the potential risks shortly before the examination.

Breastfeeding

Some radiopharmaceuticals accumulate in breast milk. If a radionuclide examination is necessary during lactation, a short interruption of breastfeeding is recommended. The duration of the interruption depends on the radiopharmaceutical used. If possible, the baby should be breastfed immediately before the nuclear medicine examination.

The mother should be encouraged to pump her milk during the interruption, which is beneficial for her own well-being by preventing milk stasis and for maintaining a continuous milk production. The pumped milk must be discarded. If a nuclear medicine examination is desired for a breastfeeding mother, the nuclear medicine department should be contacted in advance.

Adverse reactions to radiopharmaceuticals are very rare, occurring in about 1 in 100,000 cases. This risk is approximately 1,000 times lower than that associated with X-ray contrast agents.

As with any intravenous injection, there is a risk of anaphylaxis with radiopharmaceuticals, but this risk is extremely small, and most reactions are mild. No deaths due to radiopharmaceuticals have been reported worldwide in recent years. Clinical manifestations of side effects are categorized into anaphylactoid immediate reactions (nausea, vomiting, hypotension, incontinence, syncope, skin flushing with tachycardia), allergic delayed reactions (rash, urticaria, itching, shortness of breath, chest pain, palpitations, and tachycardia), pyrogenic reactions (fever, headache), various reactions (metallic taste, cyanosis, chills), and vasovagal reactions, although the latter cannot be definitively attributed to the radiopharmaceutical. Typically, these side effects are mild and usually do not require special treatment. Side effects from radiopharmaceuticals are rare, occurring in about 0.001–0.006% of cases.

In a comprehensive study from the USA, the prevalence of radiopharmaceutical-related side effects was found to be 0.0023%. This study included 783,525 examinations conducted in 18 institutions over a period of 5 years. In total, only 18 side effects were reported, none of which resulted in permanent damage or adverse outcomes for the affected individuals.

Nuclear medicine is a medical specialty that uses radioactive isotopes or radioactive chemical compounds, known as radiopharmaceuticals (radioactive drugs), for diagnosis or therapy. These procedures are commonly referred to as "scintigraphy," "scans," or "isotope studies." 

The primary focus of nuclear medicine examinations is to assess the function of organs, tissues, and bones. This functional information helps to better define certain diseases and their causes, leading to more effective treatment. In contrast, other imaging techniques, such as X-rays or ultrasound, primarily provide structural information about organs, tissues, and bones. 

Nuclear medicine examinations are not competitors to other imaging techniques but are often a valuable complement in the diagnostic process. Each year, millions of nuclear medicine examinations are performed worldwide; they are safe and involve minimal discomfort. There are many different nuclear medicine examinations, each utilizing specific radiopharmaceuticals to evaluate different parts of the body. 

This examination involves using a small amount of a radioactive substance (radiopharmaceutical) to create images that show its biodistribution in the body. These images contribute to a more precise diagnosis of the disease.

To perform a nuclear medicine examination, a radiopharmaceutical, which is a drug labeled with a radioactive isotope, is administered. Radiopharmaceuticals are usually given by injection into a vein in the arm, and less commonly by oral ingestion or inhalation. The radioactive isotopes frequently used for labeling include Technetium-99m (99mTc), Iodine-123 (123I), Indium-111 (111In), Fluorine-18 (18F), and Gallium-68 (68Ga). 

The choice of isotope depends on its physical properties and its ability to bind to the substance being labeled. The most commonly used isotope for diagnostic purposes is Tc-99m, which is ideal for scintigraphy and has a very short physical half-life of only 6 hours. (Half-life: the time it takes for the original activity to decrease by half). Due to the normal excretion of radiopharmaceuticals, such as through urine, their residence time in the body is much shorter than the physical half-life of the radioactive isotope. 

Radiopharmaceuticals are administered in trace doses, meaning very small amounts, and generally do not cause pharmacological effects. Therefore, they do not interfere with the physiological processes being studied. This differentiates them from other drugs, where a dose-response relationship exists (i.e., specific effects are induced depending on the dosage, such as lowering blood cholesterol or blood sugar levels). 

The radiopharmaceutical remains in your body temporarily and is excreted through normal bodily functions, primarily through urine. Adequate fluid intake helps promote this excretion. 

A gamma camera or PET scanner is a large piece of equipment that can be quite impressive and sometimes intimidating. It operates differently from an X-ray machine, which uses a strong X-ray beam to penetrate the patient and quickly expose the film behind them. 

In contrast, a gamma camera uses a suitable detector to capture the radiation emitted by the patient over a longer period, due to the administration of the radiopharmaceutical. The detector head of the gamma camera is positioned above or below the patient being examined. The collected data is stored in a computer for subsequent analysis. During standard imaging, the detector head of the gamma camera remains stationary once it is positioned for the scan. 

In Single Photon Emission Computed Tomography (SPECT), the gamma camera detector head moves around the patient being examined. In contrast, in Positron Emission Tomography (PET), which is often combined with CT or MRI in what are known as hybrid scanners, the detector is positioned in a ring around the patient. These techniques provide a three-dimensional representation of the distribution of activity within the body. Such examinations may take longer and require the patient to remain still for an extended period; however, staff are present to assist and monitor the patient throughout the entire procedure. 

Nuclear medicine exams primarily provide information about the function and metabolism of various organs. Typically, a radioactive substance is injected into a vein in the arm (though rarely, it may be inhaled or ingested). Since different metabolic processes occur at varying speeds, the time required between administering the radiopharmaceutical and the actual examination can vary greatly. It can be as short as a few minutes or as long as several days.

The time a patient must spend at the gamma camera can also vary for different reasons, ranging from a few minutes to, in rare cases, over an hour. The nuclear medicine staff will explain the specific details of your situation. These explanations will also cover various preparations, such as whether you need to fast, if you should avoid fasting, whether you need to empty your bladder before the exam, and any specific dietary instructions.

After a waiting period, images (scintigrams) will be taken using an appropriate imaging device (gamma camera, PET scanner).

The required waiting time - from the injection to the start of the examination (beginning of scintigraphy) - depends on the type of exam and can range from a few minutes to several hours. During longer waiting periods, you may leave the department temporarily.

The duration of the examination itself ranges from half an hour to an hour. During the exam, you need to lie still (rarely, you may sit or stand briefly). Movement during the scan can distort the images and make interpretation difficult or even impossible.

The exam is not painful. If you have painful conditions, such as bone or joint issues, please inform us. We will do our best to minimize any discomfort during the exam through appropriate measures.

Usually, it is not necessary to remove your clothing. After the examination, no specific behavioral measures are required; you can go home (or back to your department) or return to work.

In most cases, no special preparations are required - you can eat, drink, and continue taking your usual medications. However, in some specific instances, certain preparations may be necessary, and you will be informed about these details directly. 

You should inform the staff about medications, pregnancy and breastfeeding. 

For most examinations, there is no need to stop taking your medications. If any specific instructions are necessary, you will receive this information during the registration process. 

Discomfort is generally limited to the injection (similar to a blood draw) and the need to lie still. The injection of the radioactive drug does not affect your well-being or your ability to drive a vehicle. 

Only in very rare cases (1 to 6 per 100,000 examinations) are mild allergic or circulatory reactions observed, and a direct connection is not always confirmed. Please inform us of any sensations or reactions you experience. 

The amount of radioactivity used is minimal. The radiation exposure is comparable to that of an X-ray examination and ranges from one to ten times the natural background radiation that everyone is exposed to. 

Yes, children can also be examined. The dosage of radioactivity is adjusted based on the child's age and weight. Depending on the type of examination and the child's condition, sedation (administering calming medications or short-term anesthesia) may be required. The examination is not dangerous for children and does not cause any adverse effects. 

During pregnancy, nuclear medicine examinations, like X-rays, should generally be avoided because an unborn baby is more sensitive to radiation than children or adults. 

If you are pregnant or might be pregnant, please inform your doctor. 

If you have old reports and images, please bring them with you to all your appointments. Often, these previous images (including any X-rays) are needed for direct comparison. 

The substances used (tracers) behave differently in the body, so it often takes several hours before an imaging procedure can be performed. As a result, someone who arrives later than you might be called in before you due to the nature of their examination. 

The order in which you are called for your examination depends solely on the type of procedure, not on your arrival time at the clinic. 

Please arrive about 15 minutes before your scheduled appointment to handle any organizational matters. Also, ensure you bring a correct referral. 

After the final imaging is completed, please wait in the designated patient area near the examination room so we can check if all your images were properly captured. This allows us to immediately repeat or adjust any images if necessary, without having to ask you to return for another appointment. 

Afterward, you can eat, drink, and go wherever you like. You may be advised to drink plenty of fluids to help expedite the elimination of the radioactive substance, and to frequently empty your bladder. 

However, it’s best to avoid close contact with children to prevent unnecessary radiation exposure to them. Close contact means having a child sit on your lap for more than half an hour or being very close to you. 

Typically, the results are sent to the referring provider (such as your primary care doctor, specialist, or hospital department) for review and interpretation. 

However, if you would like the nuclear medicine physicians to explain the results to you directly, please inform the medical staff during your examination, and they will be happy to arrange a discussion for you. 

Typically, you can collect your results from your referring doctor no later than two business days after the examination. Physical copies of scan images are generally not provided to patients.