What is a PET/CT scan?
PET is an acronym for Positron Emission Tomography. PET is a test that uses special imaging and a radioactive type of sugar to produce pictures of the body function and metabolism of cells in the body.
CT stands for Computed Tomography. CT is an X-ray test that generates a detailed view of the anatomy or structure of organs and tissues in the body. The CT scan can show the dimension of vessels, lymph nodes and organ systems.
A PET/CT scan can depict both technologies using a single machine. It provides a picture of function (PET), a picture of anatomy (CT) and a merged picture of both the body’s metabolism and structure.
What is PET/CT most often used for?
PET scans are most often used to detect cancer and to examine the effects of cancer therapy. These scans can be performed on the entire body for a range of cancer types. In oncology, PET permits a physician to accurately image many organs of the body with a single scan in order to detect malignancy. PET has demonstrated usefulness in cost-effective whole-body metastatic surveys, avoiding costly biopsies.
PET scans of the heart can be used to help evaluate signs of coronary artery disease by determining blood flow to the heart muscle.
PET scans of the brain are used to evaluate patients who have memory disorders of an undetermined kind or other central nervous system disorders. PET can distinguish benign from malignant tumours in the brain and distinguish tumour from scar tissue, locate the focus of seizures for some patients with epilepsy, more accurately assess tumours and other sites in the brain for delicate surgery.
PET/CT can diagnose Alzheimer’s and other dementias for early intervention. As well, PET can assess Parkinson’s disease and Huntington disease.
What is the difference between a PET/CT and a regular CT or MRI?
One of the main differences between PET scans and other imaging devices such as CT and MRI is that the PET scan reveals the cellular level metabolic changes occurring in an organ or tissue. This is important and unique because the disease processes often begins with functional changes at the cellular level. A PET scan can often detect these very early changes, whereas a CT or MRI detect changes later as the disease begins to cause changes in the structure of organs or tissues.
What are the main benefits of PET/CT Scanning?
PET/CT helps physicians diagnose, stage and treat cancer with more accuracy than ever before. The exam can provide answers to the following critical questions:
– Where is the tumor?
– Is it spreading?
– How large is it?
– What is the optimal therapy?
– Is the therapy working?
– Is there a recurrence?
Other potential benefits include:
– Improves diagnostic confidence for patients who have or may have cancer.
– Reduces the need for invasive procedures, like biopsy or surgery.
– Helps avoid the “wait and see” method, often used to monitor potential disease.
– Monitors patients’ response to treatment to ensure the treatment is working.
– Helps oncologists reduce the amount of healthy tissue that is treated.
– Frequently identifies previously unsuspected cancer-bearing tissues.
– Allows for more effective and tailored treatments.
– Makes it easier to diagnose patients with head and neck cancer and melanoma, two formerly hard-to-detect cancer types.
– Provides greater diagnostic accuracy with a variety of cancers including lung cancer, lymphoma and Hodgkin’s disease, pancreatic cancer and ovarian and cervical cancers.
When disease occurs, the biochemistry of the body’s tissues and cells transform. In diseases, like cancer, the metabolic activity of the malignant cells increases thus requiring a higher glucose uptake and utilization. When a small amount of a radioactive tracer called FDG (fluorodeoxglucose), is injected into the patient, it travels through the body and accumulates in cells which then emit signals that are captured by the PET/CT scanner and then transformed into images of biological function.
Are there risks associated with PET/CT Scans?
The risks associated with PET/CT scans are very minimal. There are no side effects to having a PET/CT scan. It is completely painless and non-invasive. The quantity of FDG is kept to a minimum. FDG has a half-life of 110 minutes, so it is quickly expelled from the body and poses no threat to family members exposed to the patient following the scan.
What happens after the scan is finished?
After the radioactive tracer is processed by the organ being studied and the scanner records the information, the images are interpreted by Dr. Kevin Tracey, MD, FRCPC, ABNM, a specialty certified nuclear medicine practitioner with extensive training in PET/CT imaging.
A PET/CT scan is done on an outpatient basis. Once injected with the radioactive tracer, it typically takes 45 minutes to an hour for the tracer to travel throughout the body and be absorbed into the organ that is being examined. The scan itself takes another 30 to 60 minutes to perform.
Results from scans are read and interpreted. Following the interpretation and review of the images, a report is written and delivered to your doctor within 2-3 days.
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PREPARING FOR A PET/CT PROCEDURE
What about eating?
You should not eat for 6 hours prior to your scan appointment time. You should not eat or drink meal supplements or liquid food for 6 hours prior to your appointment time.
What about drinking?
Prior to your appointment you should drink plenty of plain water, but please avoid water which is flavoured.
What about my regular medications?
Please continue to take your usual medication on the day of the scan including pain killers. Bring your medication with you should it coincide with your scan time. If you are a diabetic patient, please make sure that the Patient Referral Centre is aware of this at booking. You will receive special instructions for your scan. Please make sure that you follow the advice given or you might not be able to have the scan.
What about physical activity?
Please avoid strenuous physical activity for 24 hours before the scan e.g. Horse riding, exercising in the gym. What should I wear? Please leave all jewellery at home and wear comfortable clothes that contain little metal, a tracksuit is ideal. Some patients feel cold in the mobile trailor even on a warm day, so please bring warm clothes, such as a fleece or a jumper to wear. You will not normally change in to a gown for the scan and will remain in your clothes, female patients will be asked to remove their bra just prior to scan.
What happens right before the scan?
Before the scan you will be given an injection (usually in the arm) of a low-dose radioactive form of glucose tracer, which allows the measuring of the activity of cells in different parts of the body. After a rest period of about an hour, a scan is then carried out which is painless and usually takes about 30 minutes. The scan is a sophisticated type of X-Ray that creates a three-dimensional picture of the inside of the body. The images taken produce a detailed picture of the internal anatomy and function. These images will allow your doctor to plan any treatment required more accurately.
How long does the scan take?
The scan procedure takes approximately 2 hours.
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DURING YOUR PROCEDURE
What happens on the day of the scan?
You should arrive 15 minutes before your scan appointment time. If you realize that you will be late or unable to attend the unit please contact the Patient Referral Centre:519.254.5555. After you have been greeted at reception, a member of staff will explain the procedure. Please feel free to ask any questions regarding the PET/CT scan at this point. A member of staff will then take a short medical history from you to assist the doctor who reads the scan. The PET /CT Technologist will then inject a small amount of 18FDG (low-dose radioactive form of glucose) into a vein in your arm. This is a colourless liquid used in the scan. You will then rest for approximately 1 hour prior to your scan. During this rest period you will be asked not to talk, as this can affect the distribution of the tracer. Depending on the the type of scan your doctor has requested, you may be able to read or listen to music during this period so please bring a book or personal music device with you. The rest period is to allow the body time to take up the injection. You will then be asked to visit the toilet to empty your bladder prior to your scan. This is to ensure the bladder is empty and gives a good view of the pelvic region. Following this you will be taken through for your scan, which will last approximately 30 minutes.
What will I experience during and after the procedure?
Except for intravenous injections, most nuclear medicine procedures are painless and are rarely associated with significant discomfort or side effects.
When the radiotracer is given intravenously, you will feel a slight pin prick when the needle is inserted into your vein for the intravenous line. When the radioactive material is injected into your arm, you may feel a cold sensation moving up your arm, but there are generally no other side effects.
For the scan you will be asked to lie flat on a narrow scanning table. It is important that you remain still while the images are being recorded. Though nuclear medicine imaging itself causes no pain, there may be some discomfort from having to remain still or to stay in one particular position during the imaging process.
Once the scan is complete you will then be free to leave the PET/CT unit.
What precautions do I need to take after the scan? Please avoid prolonged close contact with children and pregnant women for 6 hours after the scan. You should drink plenty of water to help flush the radioactive material out of your body as instructed by the nuclear medicine personnel.
How much radiation do I receive from the scan?
The equivalent to a period of a few years natural background radiation for each part of the scan (PET and CT scans). The radiation injected for the scan fades over time, with most of it decaying in the first 6 hours. The radiation has a very short physical half-life (the time taken to reduce the radioactivity by half).
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AFTER YOUR PROCEDURE
What do I do after the scan?
You should continue to drink plenty of fluids for the remainder of the day. After the scan you can eat and drink normally, so please bring something with you to consume on your way home. How do I get my results? The scan is usually reviewed within 48 hours and the result will be sent to the doctor who referred you for the PET/CT scan.
Please make every effort to keep your appointment. If you must cancel or reschedule, notify our office at least 24 hours in advance. The FDG (sugar water with a radioactive tracer) used for your scan is prepared specifically for you and will have to be discarded if you fail to keep your appointment.
Consult your physician prior to your PET/CT scan if…
– You are or may be pregnant
– You are allergic to any food or drug
– You are currently being treated for an infection
– You are unsure if you should take your medications
– You have had recent radiation therapy
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