Radioisotopes and Radiotherapy - Day in the Life Story

NUCLEAR MEDICINE – Personal Profile

The Job of a Nuclear Medicine Technologist (NMT)

Fran Maestrale of Frankston Hospital

Nuclear medicine is a diagnostic imaging modality often situated within the X-ray department in hospitals (private and public) or in private clinics. Most nuclear medicine departments are relatively small with only a few NMTs at each site. It is a science that investigates the physiology of the human body. We are often asked to perform tests for our patients to determine or differentiate a type of pathology. Unlike general X-rays, nuclear medicine is not concerned with the structure of organs, or the way they physically appear, but rather how they function. Once introduced into the human body the distribution of the radiopharmaceutical in a normal, healthy human is known and depending on how this changes in our patients will help diagnose the pathology the doctor is questioning.

A nuclear medicine technologist (NMT) performs many procedures each day. Prior to the first patient arriving, the technologist must measure the amount of radioactivity delivered to their department. We obtain our daily supply of radioisotope from Radiopharmacy Central in Victoria, who order it on our behalf from the nuclear reactor at Lucas Heights in NSW. The amount of radioactivity is measured in a well counter (which is an instrument used to determine the level of radioactivity present). This isotope, in liquid form, is then drawn up into the required amounts and added to ‘cold’ kits (to form a radiopharmaceutical) so that the day’s scans can be performed. A cold kit is a vial containing a particular chemical agent that once introduced into the human body will travel to a particular organ.

We can do many tests to determine how well an organ is functioning or to what extent it has been damaged. Each test uses a particular compound, which travels to a known organ of the body based on its chemical composition and the way it is introduced into the body. Once we have introduced the radiopharmaceutical into the patient’s body, either through intravenous injection, inhalation or ingestion, images are acquired using a gamma camera. The radioisotope used emits gamma rays that interact with the scintillation crystal in our gamma camera to reveal the distribution of the radiopharmaceutical compound.

Most of our diagnostic procedures involve intravenous injection and once the compound has been injected it travels through the venous system of the body to the heart and then through the arterial system to the organ under investigation where it is absorbed. Other tests, such as those investigating the gastrointestinal system, require the compounds to be ingested. This enables us to track the movement of it through the stomach and bowel. When conducting tests to look at the lungs we use a machine that incorporates the isotope into tiny balls of carbon, called microspheres, which are then inhaled by the patient.

The majority of patients referred to nuclear medicine departments require bone scans. These may be performed to diagnose cancer, investigate the extent of arthritis, screen for fractures that do not show on a plain X-ray, or look at infection of the bone. The cold kit we use for these scans contains a phosphate compound which is labelled to the isotope 99m-technetium. The mixture is injected intravenously into our patients and the phosphate is absorbed onto the surface of all the bones in the skeleton.

In other cases where the blood rather than the bone is of interest, we can label the blood of a patient (that is, mixing it with a small amount of radioactivity). This can be used to locate the site of an internal bleed. Once the bleed has been located, these patients can go to surgery and the surgeon will know where to begin in finding the haemorrhaging vessel so that it may be sealed to prevent further blood loss.

Another test we perform is one to determine how healthy the heart is. After labelling the patient’s blood we take images of the heart beating to determine how much blood the heart pushes out of the left ventricle every time it contracts. This test is often performed on patients undergoing, or about to commence chemotherapy as some of the chemotherapy chemicals are toxic to the heart and affect its efficiency.

We often perform tests on the kidneys to determine how well they are functioning. Using different radiopharmaceuticals we can investigate how well blood is flowing to the kidneys, determine whether due to recurrent kidney infections the kidneys have become scarred thereby hampering their function, or determine whether narrowed blood vessels feeding the kidneys are responsible for causing high blood pressure.

Nuclear medicine often works in conjunction with the other imaging modalities such as CT and X-ray. Sometimes a mass may be seen within the body on a CT scan but the doctors are uncertain whether it is scar tissue from past trauma or a tumour growing, as these look very similar on a CT scan. Nuclear medicine is then called upon to distinguish between these two possibilities. An isotope called Gallium (atomic number 67) interacts with markers on tumour cell membranes but is not taken up by scar tissue. Therefore, this isotope may be used to locate any sites of tumour (such as Non-Hodgkin’s Lymphoma) within the body.

Thallium-201 is another common radioisotope that is used. We use this tracer to investigate narrowed blood vessels within the heart that provide oxygen and nutrients to the heart muscle. Many people who complain of chest pain, suffer from angina, which is a condition where the blood (and therefore oxygen) supplied to the muscle is not sufficient when exercising. We can use nuclear medicine to inform the cardiologist which blood vessel is affected so that it may be repaired, allowing sufficient blood flow to be restored.

Our typical day (9 am to 5 pm, Monday to Friday) consists of performing a number of these different tests, looking at a variety of different pathologies. Most departments see mainly adults but some provide nuclear medicine services for children and neonatals. NMT’s must be familiar with the physiology of many organs in the body in order to know whether the images obtained appear normal or abnormal. We also have the opportunity to learn about the various treatments for different conditions we can suffer from. Although through practice we may be able to interpret the images and determine what pathology a patient is suffering from, we are not qualified to do this. The NMT must present the images to the radiologist who is responsible for making a diagnosis. Due to the nature of our profession, we have a close working relationship with radiologists, surgeons and nurses.