What is positron emission tomography – computed tomography (PET-CT) scanning
Positron emission tomography, also called PET imaging or PET scanning, is a type of imaging diagnostics of nuclear medicine that we can assist you with.
Nuclear medicine imaging uses small amounts of radioactive material to diagnose, evaluate or treat various diseases. These include many types of cancer, heart disease, gastrointestinal, endocrine or neurological disorders and other abnormalities. Because examinations performed through nuclear medicine can determine molecular activity, they have the potential to identify the disease in its earliest stages and determine whether the patient is responding to treatment.
Nuclear imaging procedures are non-invasive. With the exception of intravenous injections, they are usually painless. These examinations use radioactive materials to help physicians diagnose and assess a patient's medical condition.
Radioactive materials are molecules associated with or “labeled” with a small amount of radioactive pharmaceuticals that can be detected by PET scanning. Radiotrackers accumulate in tumors or areas of inflammation. They can also bind to specific proteins in the body. The most commonly used radio tracker is F-18 fluorodeoxyglucose or FDG, a glucose-like molecule. Cancer cells are more metabolically active and can absorb glucose at a higher rate. This higher percentage can be seen in PET scans. This allows your doctor to identify the disease before it is seen in other imaging tests. FDG is just one of the many radio-tracking substances used in PET-CT imaging.
Depending on the type of diagnosis, the radio tracker is injected, swallowed or inhaled as a gas. Eventually it accumulates in the area of the studied body. A special camera or imaging device detects radioactive emissions from the radio transmitter. The camera or device produces images and provides molecular information.
Many centers superimpose images of nuclear medicine with computed tomography (CT) or magnetic resonance imaging (MRI) to obtain special views. This is known as image merging or co-registration. These overlays allow the physician to compare and interpret information from two different examinations of an image. This results in more accurate information and accurate diagnoses.
PET scanning measures important body functions, such as metabolism. It helps doctors assess how well organs and tissues function.
CT imaging uses special X-ray equipment, and in some cases contrast material, to produce multiple images from inside the body. A radiologist examines and interprets these images on a computer monitor. CT images provide excellent anatomical information.
Combined PET-CT scanners perform almost all PET scans today. These combined scans help determine abnormal metabolic activity and can provide more accurate diagnoses than the two scans performed separately.
What are the most commonly used procedures
Doctors perform PET and PET-CT scans to:
- cancer detection and / or diagnosis;
- determine if the cancer has spread to the body;
- to evaluate the effectiveness of treatment;
- determine if the cancer has returned after treatment;
- evaluate the forecasts;
- to assess tissue metabolism and viability;
- to determine the effects of myocardial infarction;
- identify areas of the heart muscle that would benefit from angioplasty or coronary artery bypass grafting;
- to assess brain disorders such as tumors, memory disorders, seizures and other disorders of the central nervous system;
- mapping of normal human brain and heart function.
How to prepare for a PET-CT scan
You may wear loose clothing during the examination.
Women should always tell their doctor and technologist if they are likely to be pregnant or breast-feeding.
Tell your doctor and technologist who will perform your test on all medications you are taking, including vitamins and supplements. List all allergies, recent illnesses and other medical conditions.
You will receive specific instructions based on the type of your scan. Patients with diabetes will receive special instructions for preparing for this type of test.
If you are breast-feeding during the test, ask your radiologist or doctor how to proceed. It may help to pump the milk before the test so that it can be stored for the subsequent procedure for use, while the PET radio-tracking and CT contrast material is no longer in your body.
Leave metal objects at home, including jewelry, glasses, dentures and hairpins, as they can affect CT images. You may need to remove hearing aids and a removable dental prosthesis.
Your doctor will usually tell you not to eat anything for a few hours before the whole body PET-CT scan. Eating can change the distribution of the PET marker in your body and can lead to suboptimal scanning. This may require you to repeat the scan on another day, so following the feeding instructions is very important. You should not drink liquids containing sugars or calories for several hours before the scan. It is recommended to drink water instead. If you are diabetic, your doctor may give you special instructions. Tell your doctor about all the medicines you are taking. List any allergies, especially to contrast materials or iodine.
What the equipment looks like
PET scanner is a large machine with a round hole in the shape of a tunnel. It looks similar to CT or MRI. Numerous detector rings inside the machine record the energy emissions of radio particles in your body.
The CT scanner is usually a large machine with a short tunnel shape in the center. You will lie on a narrow inspection table that slides out and out of this short tunnel. Rotating around you, the X-ray tube and electronic X-ray detectors are located opposite each other in a ring called a socket. The computer workstation that processes the image information is located in a separate control room. Here the technologist controls the scanner and monitors the test in direct visual contact. The technologist will be able to hear and speak with the help of a speaker and a microphone.
The computer helps to create images from the data received from the gamma camera.
How the procedure is performed
Ordinary X-rays create an image by passing X-rays through the body. Nuclear medicine tests use a radioactive material called a radiopharmaceutical or radiotracker. This material is injected into the blood, swallowed or inhaled as a gas. The material accumulates in the studied area of your body, where it releases a small amount of energy in the form of gamma rays. Special cameras detect this energy and use a computer to create images that offer details of the structure and function of organs and tissues.
Unlike other imaging diagnostics, nuclear medicine tests focus on processes in the body, such as metabolic rates or levels of various other chemical activities. Areas of greater intensity, called “hot spots”, indicate where large amounts of radiotrackers have accumulated and where there is a high level of chemical or metabolic activity. Less intense areas or “cold spots” indicate lower radiotracker concentration and less activity.
What is the procedure
The treatment of nuclear medicine is performed on outpatients and hospitalized patients.
You will lie on a medical table. If necessary, a nurse or technologist will insert a venous catheter into a vein in your arm.
Radiotrackers usually take about 30-60 minutes to pass through your body and be absorbed by the test area. You will be asked to rest in peace and avoid movement and talking.
You may be asked to drink a small amount of contrast agent, which will be localized in the gut and help the radiologist interpret the test.
You will be moved to the PET-CT scanner to begin imaging. You will need to remain still during the test. The CT scan is performed first, followed by a PET scan. Sometimes the second CT test with intravenous contrast will follow the PET scan.
The total scan time is usually about 30 minutes.
Depending on which area is being studied, additional tests involving other trace substances or drugs may be used. This can extend the time for the procedure to three hours. For example, if you have been tested for heart disease, you may have a PET scan both before and after exercise, or before and after taking drugs that increase blood flow to the heart.
When the test is complete, you may be asked to wait until the technologist checks the images in case more images are needed. Sometimes more images are obtained to clarify or better visualize certain areas or structures. The need for more images does not necessarily mean that there was a problem with the test or that abnormalities were found. You do not have to worry while waiting for the processing and receiving the final diagnosis.
What will I experience during and after the procedure
With the exception of intravenous injections, most nuclear medicine procedures are painless. They are rarely associated with significant discomfort or side effects.
When the radiotracker is given intravenously, you will feel a slight sting when the needle is inserted into your vein behind the intravenous line. You may feel a feeling of cold moving on your arm when the injection radio tracker moves. There are generally no other side effects.
Some procedures may require a catheter, which can cause temporary discomfort.
It is important to stay still during the test. The image itself does not cause pain. However, you must remain still or remain in a certain position during the test, which may cause you discomfort.
If you are afraid of confined spaces, you may feel anxious during the test.
Unless your doctor tells you otherwise, you can resume normal activities after the test. A technologist, nurse or doctor will provide you with all the necessary special instructions before you leave.
The small amount of radiotracker in your body will lose its radioactivity over time through the natural process of radioactive decay. It can also come out of your body through your urine or faeces during the first few hours or days after the test. Drink plenty of water to help flush radioactive material out of your body.
Who interprets the results and how to get them?
A radiologist or other doctor specially trained in nuclear medicine will interpret the images and send a report to your reference doctor.
If your doctor has ordered a diagnostic computed tomography scan, a radiologist with specialized training in interpreting CT scans will send a report to your reference doctor.
What are the benefits and risks?
Nuclear medical examinations provide unique information – including details about the function and anatomy of body structures, which is often unattainable with the help of other imaging procedures.
A scan of nuclear medicine provides the most useful diagnostic or treatment information for many diseases.
Scanning is cheaper and can provide more accurate information than investigative surgery.
By identifying changes in the body at the cellular level, PET imaging can detect the early onset of the disease before being apparent in other imaging tests such as CT or MRI.
The advantages of combined PET / CT scanning include:
- larger details with a higher level of accuracy, as both scans are performed simultaneously without the patient having to change positions, there is less room for error;
- greater convenience for the patient who undergoes CT and PET at once rather than twice at different times.
Because only a small dose of radiotracker is used, nuclear medicine tests have relatively low radiation exposure. This is acceptable for diagnostic examinations. Thus, the radiation risk is very low compared to the potential benefits.
Diagnostic procedures for nuclear medicine have been used for more than five decades and no long-term adverse effects of such low-dose exposure are known.
The risks of treatment are always weighed against the potential benefits of therapeutic procedures in nuclear medicine. Your doctor will inform you of any significant risks before treatment and give you the opportunity to ask questions.
Allergic reactions to radiotrackers are extremely rare and usually mild. Always tell your radiologist about any allergies you may have or other problems that may have occurred during a previous test.
Injection of a radiotracker may cause mild pain and redness.
What are the limitations of positron emission tomography – computed tomography (PET-CT)
Nuclear medicine procedures can take a long time. It may take several hours to days for the radio to accumulate in the area you are interested in, and image execution may take up to several hours. In some cases, newer equipment can significantly shorten the procedure time.
The image resolution of nuclear imaging may not be as high as that of CT or MRI. However, PET-CT scans are more sensitive to different indications, and the functional information they provide is often not available from other imaging techniques.
Altered blood sugar or blood insulin levels may adversely affect test results in patients with diabetes or patients who have eaten several hours before the test.
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