Positron Emission Tomography (PET) – Uses, Procedure & Side Effects

The life we recognise too late is in the living, the tissue of each day and hour. This proverb tries to say that you must act good immediately in the right situation in your life so that you don’t have to worry in the future about the past situation that you left earlier. It also means that if you ignore taking the correct steps now, you might be worrying about this situation in the future. Each and every hour is like a tissue in the body, which must be functioning correctly at the right time. This proverb also highlights the tissue. Let’s have a look at the Positron Emission Tomography (PET) test, which helps diagnose the metabolic functioning of your tissues.

What is Positron Emission Tomography (PET)?

A positron emission tomography (PET) scan is an imaging test that helps in finding out the biochemical or metabolic functioning of your organs and tissues.

A PET scan can identify the atypical metabolism of the disease’s tracer. This will be prior to the disease showing up on other imaging tests, like computerised tomography (CT) and magnetic resonance imaging (MRI).

In this PET method, a radioactive drug known as a tracer is used, which shows both typical and atypical metabolic functions. The PET-CT or PET-MRI scanner is somewhat similar to CT or MRI scanners. It is a large machine that stands upright.

PET Uses

A PET scan helps in identifying different conditions, like cancer, heart disease, and brain disorders. Your health care provider will provide the information that will help monitor, diagnose, or treat the condition.

PET scans help with the following :

• Finding out the cancer.
• Checking if your cancer has spread.
• Revealing if a cancer treatment is working.
• Diagnosing the probability of cancer. 

Several kinds of solid tumours could be identified using PET-CT and PET-MRI scans, which include:

• Breast
• Brain
• Colorectal
• Esophageal
• Cervical
• Lymphatic system
• Pancreatic
• Head and neck
• Lung
• Prostate
• Skin
• Thyroid

PET Procedure

The Positron Emission Tomography (PET) procedure takes nearly two hours to complete. You don’t have to stay overnight in the hospital for the Positron Emission Tomography (PET) procedure.

1) Before Positron Emission Tomography (PET)

At the time of your arrival for your Positron Emission Tomography (PET) scan, you will be requested to:

• Wear a hospital gown.
• Just empty your bladder.

A healthcare provider will inject the tracer into a vein in your arm or hand. You might experience a cold sensation slowly moving over your arm. You can take a rest and be silent in a reclining chair for 30 to 60 minutes, till the tracer gets absorbed by your body.

2) During Positron Emission Tomography (PET)

Once you are ready for positron emission tomography (PET), you need to lie down on a padded and narrow table. That table slowly slides into the part of the scanner whose structure is similar to a doughnut hole.

At the time of the scan, you have to be still so that the images will not be blurred. You could hear the buzzing and clicking sounds of the machine; however, the test is painless, unlike colonoscopy. If you get fear out of the enclosed spaces, then you might face some nervousness when you are inside the scanner. 

If so, you could tell your nurse, who might provide you with some medicines to relax. This procedure will take 30 minutes to finish a PET-CT scan and 45 minutes for a PET-MRI scan. 

3) After Positron Emission Tomography (PET)

Once the test is completed, you could deal with your usual routine day work, unless your healthcare provider objects to some activities. Next, you must drink an enormous amount of fluids to flush out the tracer from your body.

Side Effects of PET Scans

PET scans also have some side effects despite having huge benefits. Here are some of the possible side effects of a PET scan:

1) Radiation exposure

As mentioned above, the PET CT scans use radiation, which might increase cancer risks and other health issues over time. But, in general, only a safe amount of radiation is used in PET CT scans.

2) Allergic reactions

Though most of them are non-allergic, a few people experience an allergic reaction to the radioactive tracer that is used in PET scans. Some people have allergic symptoms like hives, itching, and difficulty breathing. In very rare cases, life-threatening anaphylaxis (a serious allergic condition) might occur. Both PET CT and PET MRI scans cause allergies in some people.

3) Nausea

When patients get the contrast material, the side effect of nausea occurs. Nausea or vomiting happens in some people after a PET CT scan. This mild effect may go away on its own within some time. 

4) Headache

Some mild headaches are a common side effect of PET CT scans, which may go away within a certain period of time.

5) Dizziness

Dizziness or lightheadedness is a common side effect in some people after a PET CT scan.

6) Pain or discomfort

Though pain or discomfort is rare after the PET CT scan, some patients might feel them at the injection site or in other body regions.

How do you prepare for a PET scan?

Your healthcare provider will inform you about how to prepare for your scan. In general, you must strictly avoid strenuous exercise for some days before the study, and you must stop eating four hours before the scan.

There are some details about which you must report to your healthcare provider. Here are the details about which you need to inform your healthcare provider:

• If you were sick recently and affected by any serious health condition, then tell your medical provider.
• Presently, you have a medical condition like diabetes.
• If you had a bad allergic reaction.
• You have taken any medicines, herbal supplements, or vitamins.
• You are pregnant, or there is a chance that you might be pregnant.
• You’re breastfeeding your kid.
• You have a fear of enclosed spaces, which is a condition called claustrophobia.

What should I expect during a PET CT scan?

You will see some general steps during the PET scan. Here are the steps you might see at the time of the PET scan : 

You will be IV injected with a radiotracer, which will have the correct quantity of a radioactive drug. Generally, fluorodeoxyglucose (FDG) is used as the radiotracer for this procedure.

You will be seated in a chair for nearly an hour while the radiotracer will move through your bloodstream. It will be absorbed by your organs and tissues.

More activities could send the radiotracer to all your body regions, which your healthcare provider isn’t testing. But you will not feel the radiotracer.

You might also get an IV injection of a contrast dye, which assists in this procedure to get sharper CT images.

During this procedure, you will lie down on an exam table that has the ability to slide in and out of the PET scanner. The PET CT scanner is shaped like a doughnut, whose opening has a diameter of about 30 inches.

During the PET scan, which usually takes about 30 minutes, the patient is required to remain still until it is complete. This is because even a slight movement might blur the images.

During the ongoing procedure, the patient might hear buzzing and clicking sounds as the scanner captures photos. A technologist who will guide you will preview the scans before you leave. This is to make sure the images are in focus.

How is a PET scan performed?

There are some general steps in the PET scan procedure. They are:

• The patient will be requested to remove jewellery, clothing, watches, or other objects that might interfere with the scan.
• If the patient was asked to remove clothing, then that patient will be provided a gown to wear.
• The patient needs to empty his or her bladder before the beginning of the procedure.
• They will start one or two IV lines in the patient’s hand or arm for the radionuclide injection. 
• Some kinds of abdomen or pelvis scans might require that a urinary catheter be inserted into the bladder in order to drain out the urine during this procedure.
• In a few cases, a primary scan might be done before the radionuclide injection, depending on the type of study being done. During that, the patient will be kept lying on a padded table inside the scanner.
• The radionuclide will be injected into the IV, and it will concentrate in the organ or tissue for nearly 30 to 60 minutes. The patient has to remain still at this time. However, the patient will be harmless to other people, as the radionuclide generates only less radiation than the usual X-ray.
• Once the radionuclide has been absorbed for a long time, the scan will start. The scanner will begin to move above the body parts that are being studied.
• Once the scan is completed, the IV line will be removed. In the event that a urinary catheter has been inserted, it will also be removed.

Though the PET scans are done on an outpatient basis, there is a possibility that a few hospital inpatients undergo a PET examination for some conditions.

How do I prepare for the scan?

There are some general instructions that you should follow before you prepare for the scan. Here are the basic instructions that you could follow:

• Frankly, tell your healthcare team about any medicines you use, including over-the-counter medicines, herbs, and vitamins. So, your healthcare provider will tell you about the medicines that you must not use before the test.
• You can ask your doctor how much insulin you must take before the scan and which foods you should eat in case you have diabetes and take insulin. Your blood sugar levels will also be monitored during the test. However, the test results are not accurate all the time for people with diabetes.
• You might be told to avoid some foods and drinks, like caffeine-containing drinks or alcohol, for at least 24 hours before your test begins.
• Also, it is important that you don’t eat and drink only water for 4 to 6 hours prior to the beginning of your test.
• Make sure that you wear comfortable and loose-fitting clothes.
• Don’t wear any jewellery or any other metal objects.
• Kindly tell your healthcare team if you have a fear of tight spaces or being enclosed.

What happens during the scan?

In general, a health care professional and a nuclear medicine technologist will do PET scans at a PET centre or in a hospital. They use special equipment to perform this scan.

• A small metal disc (electrode) will be kept by a scan technologist on your chest, arms, and legs.
• The wires on the discs connected to a machine help record your electrocardiogram (ECG or EKG). This ECG gently tracks your heartbeat at the time of the test and will signal the computer to take a scan. 
• An intravenous line (IV) is placed in your arm, and then the tracer will be injected through the IV line. You must lie on a flat table that is fixed to the PET scanner and a computer. That table will slide into the doughnut-shaped scanner.
• Inside the PET scanner, the detectors will record the tracer’s radioactive patterns in your heart. This information gets converted into images on a computer screen. Many scans are performed to generate images of thin slices of your whole heart in all directions.
• You must hold still with your arms above your head while each scan is being made. So, your healthcare team will capture a proper picture of your heart before the tracer is injected. This procedure might take about 15 to 30 minutes.
• Next will be the tracer injection in your heart, through which it will be scanned again.
• If the patient has a pharmacologic stress test( a nuclear chemical stress test), then he or she will be given a medicine that increases the blood flow in the heart. They might give medicines like adenosine, dipyridamole (Persantine), or dobutamine in this step. Then, the healthcare team will check your heart’s ability to take up the tracer before and after getting the medicine.
• The whole test takes between 1 and 3 hours.

However, in people with severe coronary artery disease, a few regions of their heart might not receive sufficient blood in cases of stress. Due to this, the tracer will not show up in those areas.

PET/MRI Scan

A PET/MRI scan simply combines images from a positron emission tomography (PET) scan and a magnetic resonance imaging (MRI) scan to generate some of the most detailed pictures of the inside of your body. These images help doctors find out about brain issues.

PET/MRI Scan Working

A magnetic field is used in MRI scans to generate detailed images of the internal structures of the body. They help find out the details of the functioning of the body parts.

On the other hand, PET scans use tracers to find abnormalities that indicate disease. However, the scientists are unable to combine PET and MRI for simultaneous scanning, as the MRI’s powerful magnets might interfere with the imaging detectors on the PET scanner.

The images obtained from PET and MRI scans that have been conducted separately are later merged.

Benefits of PET/MRI scans

There are many benefits to PET and MRI scans. They are:

• PET/MRI scans give accurate diagnosis options, as they can find abnormal findings that PET/CT misses.
• PET/MRI scans use less radiation exposure than PET/CT scans. So, the patient’s exposure to PET/MRI might be less.
• PET/MRI provides the convenience of two scans in one option.

PET/CT Scan

A PET-CT scanner combines PET scanning with CT scanning.

PET/CT Scan Working

A Positron Emission Tomography (PET) scanner generates detailed and three-dimensional images of the cells functioning inside the body. They help diagnose different cancers and show the spread of cancer or how it responds to treatment.

A computerised tomography (CT) scanner uses X-rays and a computer to get images of the inside of the body. They show up the internal organs, blood vessels, and bones.

PET-CT scans all together use a long tunnel in which the patient lies. The tunnel and the table move through it for the patient’s scan. 

Benefits of a PET-CT scan

The CT scanner component permits the reconstruction of the detailed PET images. Complex CT scans can be combined with PET scans so that the two types of images can be viewed together. This helps in the effective treatment of the disease.

Conclusion

PET scans help identify different health issues like cancer, heart disease, etc. A dome-shaped scanner is used for PET scans. Though PET scans are generally safe for patients, they have some risks and potential side effects. So, it is a big concern to discuss these risks with your doctor before you undergo a PET scan. Some prior preparations will help you undergo the PET scan very smoothly. It is better not to consume alcohol for 48 hours before any diagnostic test.

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