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Positron Emission Tomography
(PET)
Overview

A positron emission tomography (PET) scan is an imaging test that can
help reveal the metabolic or biochemical function of your tissues and
organs. The PET scan
uses a radioactive drug called a tracer to show both typical and
atypical metabolic activity. A PET scan
can often detect the atypical metabolism of the tracer in diseases
before the disease shows up on other imaging tests, such as
computerized
tomography (CT) and magnetic resonance imaging (MRI). The tracer is most often injected into a vein within your hand or arm.
The tracer will then collect into areas of your body that have higher
levels of metabolic or biochemical activity. This often pinpoints the
location of the disease. The PET images
are typically combined with CT or MRI and
are called PET-CT or PET-MRI scans.
What is a PET scan?
A positron emission tomography (PET) scan is an imaging test that produces
images of your organs and tissues at work. The test uses a safe, injectable
radioactive chemical called a radiotracer and a device called a PET scanner.
The scanner detects diseased cells that absorb large amounts of the radiotracer,
which indicates a potential health problem.
Healthcare providers frequently use PET scans to help diagnose cancer and assess
cancer treatment. They can also assess certain heart and brain issues with the
scan.
What’s the difference between a PET scan, CT scan and MRI?
Definition and Basic Principles
PET scans use radioactive
tracers to see how the body works. These tracers are
injected into a vein. They collect in areas with high
activity, creating 3D images of how well tissues and organs
are working.
This makes PET scans great for finding and tracking diseases
like cancer, heart disease, and brain
disorders.
Differences Between PET and Other Imaging Techniques
CT and MRI scans
show the body’s structure. But PET scans focus on how things
are working at the cellular level. Here’s a quick
comparison:
Imaging Technique |
Key Features |
Best Used For |
PET Scan |
Uses radioactive
tracers to show metabolic activity |
Detecting cancer, heart problems, brain
disorders |
CT Scan |
Uses X-rays to create detailed cross-sectional
images |
Diagnosing injuries, bone and joint problems,
tumors |
MRI Scan |
Uses magnetic fields and radio waves to produce
high-resolution images |
Examining soft tissues, organs, and the central
nervous system |
By using different imaging
techniques together, doctors can understand a patient’s
condition better. This leads to earlier diagnosis and more
effective treatments.
Why it's done
A PET scan
is an effective way to help discover a variety of conditions, including
cancer, heart disease and brain disorders. Your health care provider can
use this information to help diagnose, monitor or treat your condition.
Applications of PET Scans in Cancer Detection
PET scans have changed how we detect and manage cancer. They
give us deep insights into how tumors work and grow. This
helps doctors stage cancer accurately, track how treatments
work, and spot cancer coming back. It’s all about making
cancer care more personal and precise.
One big use of PET scans is in cancer
staging. They show how far cancer has spread. This helps
doctors choose the best treatment plan. Here’s a comparison
of the TNM staging system and what PET scans can show:
|
PET Scan Information |
T (Tumor) |
Determines primary tumor size and extent of local invasion |
N (Nodes) |
Detects cancer spread to nearby lymph nodes |
M (Metastasis) |
Identifies distant metastases in organs and tissues |
PET scans are also key in checking how well treatments work.
By comparing scans before and after treatment, doctors can
see if it’s working. This helps them make changes to
treatments to get better results and reduce side effects.
Also, PET scans help find cancer coming back early. They
spot small, active cancer cells before symptoms show. This
is very important for cancers like lung, breast, and colon
cancer, which often come back.
PET scans are now a big part of precision
medicine in cancer care. They work with genetic testing
to make treatments fit each patient’s cancer. This makes
treatments more effective and safer, leading to better
health and life quality for patients.
PET Scan in Alzheimer’s and Neurological Disorders
PET scans are now a key tool in diagnosing and tracking
Alzheimer’s disease and other neurodegenerative
diseases. They help find amyloid
plaques and tau
tangles in the brain. This makes it easier to spot
these brain
disorders early and track how they change over time.
Early Diagnosis and Monitoring Disease Progression
PET scans are great for catching brain changes before
symptoms show up. They spot amyloid
plaques and tau
tangles, signs of Alzheimer’s. This early catch is key
for starting treatment right away.
They also help track how these diseases get worse. By
comparing scans, doctors can see how fast the disease is
growing. This helps them check if treatments are working and
adjust plans as needed.
Heart disease
A positron emission tomography (PET) scan of the heart is an
imaging test that uses specialized dye to allow your doctor
to view problems with your heart.
The dye contains radioactive tracers, which concentrate
on areas of the heart that may be injured or diseased.
Using a PET scanner, your doctor can spot these areas of
concern. A heart PET scan is typically an outpatient procedure,
meaning you will not have to stay at the hospital
overnight. This is typically a same-day procedure. Your doctor may order a heart PET scan if you’re
experiencing symptoms of heart trouble.
Symptoms of heart trouble include:
- irregular heartbeat (arrhythmia)
- pain in your chest
- tightness in your chest
- trouble breathing
- weakness
- profuse sweating
Your doctor may also order a heart PET scan if other
heart tests, such as an echocardiogram (ECG)
or cardiac stress
test, don’t provide your doctor with enough
information. A heart PET scan can also be used to
track the effectiveness of heart disease treatments. Brain disorders
Glucose is the main fuel of the brain. During PET scans,
tracers are “attached” to compounds such as glucose. By
detecting radioactive glucose, the PET scan can show which
areas of the brain are using glucose at the highest rates.
When a specialist interprets the scan, they can see how the
brain is working and check for any irregularities.
PET scans are used to help diagnose and manage many CNS
disorders, including:
- Alzheimer’s disease
-
depression
- epilepsy
- head trauma
- Parkinson’s disease
Cardiovascular Evaluation with PET Scans
PET scans are a key tool for checking heart health and
finding problems early. They show detailed images of blood
flow and heart
function. This helps doctors spot issues and plan the
best treatments.
This non-invasive method is vital for spotting coronary
artery disease. It’s a major cause of heart attacks and
other heart problems.
Assessing Blood Flow and Heart Function
PET scans are great for checking how well blood flows to the
heart. They use a special tracer to see where blood might
not be reaching. This shows if there are blockages or narrow
spots in the arteries.
They also look at how the heart uses energy. This is helpful
for patients with heart failure or other heart issues. It
helps doctors find parts of the heart that can get better
with the right treatment.
Detecting Coronary Artery Disease
Coronary artery disease is a big risk to heart health.
It happens when plaque builds up in heart arteries. PET
scans are very good at finding this problem early.
They spot where blood flow or energy use is off. This helps
doctors know where and how bad the problem is. Early
detection is key to stopping the disease from getting worse.
With PET scans, doctors can create a treatment plan. This
might include changing lifestyle habits, taking medicine, or
surgery. Regular PET scans help see if treatments are
working and make changes if needed.
When would I need a PET scan?
In general, a PET scan can measure vital functions, such as blood flow, oxygen
use and blood sugar (glucose) metabolism. It can also identify organs and
tissues that aren’t working as they should.
If your healthcare provider suspects you may have cancer, they’ll likely
recommend a PET scan, which can detect cancer and/or make a diagnosis.
If you’ve already been diagnosed with cancer, your provider may recommend more
than one PET scan throughout your treatment to:
- Determine whether the cancer has spread in your body (metastasized).
- Assess the effectiveness of treatment.
- Determine if the cancer has returned after treatment (recurred).
- Evaluate the prognosis (outlook) of the cancer.
If you’re having heart issues, your provider may recommend a PET scan to:
- Determine the effects of a heart attack on areas of your heart.
- Identify areas of the heart muscle that would benefit from angioplasty or coronary
artery bypass surgery.
If you’re experiencing neurological symptoms, your provider may recommend a PET
scan to evaluate possible brain abnormalities, such as tumors, seizures and
other central nervous system conditions.
Test Details
How does a PET scan work?
A PET scan is a type of nuclear medicine imaging. Nuclear medicine
uses small and safe amounts of radioactive material, called
radiotracers, given through an IV.
Unlike other imaging techniques, PET scans focus on processes and
molecular activity within your body. This gives them the potential
to find disease in its earliest stages.
Diseased cells in your body absorb more of the radiotracer than
healthy ones do. These are called “hot spots.” The PET scanner
detects this radiation and produces images of the affected tissue. A
PET/CT scan combines X-ray images from a CT scan with PET scan
images.
Radioactive Tracers and Their Role
Before a PET
scan, a small amount of radioactive tracer, like
fluorodeoxyglucose (FDG), is injected into the patient. This
tracer goes to cells that use a lot of glucose. Cancer
cells, for instance, use more glucose than normal cells.
The Imaging Process
During the scan, the patient lies on a table that moves
through a scanner. As the tracer decays, it releases
positrons that hit nearby electrons, creating gamma rays.
The PET scanner catches these rays and makes detailed 3D
images of where the tracer is in the body.
Interpreting PET Scan Results
Radiologists look at PET scan images and calculate standardized
uptake values (SUVs). SUVs show how much tracer a body
part has taken in. This helps spot areas with unusual
glucose use. Here’s a table showing SUV ranges for normal
and cancerous tissues:
Tissue Type |
Typical SUV Range |
Normal Tissue |
0.5 – 2.5 |
Cancerous Tissue |
2.5 – 10.0+ |
By looking at PET images and SUVs, radiologists can find
problems and give important health insights.
How do I prepare for a PET scan?
PET scans are an outpatient procedure, which means you go home the
same day. Your healthcare provider will give you detailed
instructions on how to prepare for the scan. In general, you should:
- Make sure your provider has a current list of all medications,
Vitamins and supplements you take, as well as any allergies you
have.
- Alert your provider if you think you could be pregnant or
if you’re breastfeeding.
- Not eat anything for six hours before the test. Your healthcare
provider may change this direction if you have diabetes.
- Drink only water.
- Avoid caffeine for
24 hours before the test if you’re being tested for a heart
problem.
- Wear comfortable clothes and leave metal accessories, such as
jewelry, eyeglasses, dentures and hairpins at home.
- Tell your healthcare provider if being in an enclosed space
makes you anxious. You may be able to take a mild sedative to
help you relax during the procedure.
What should I expect during a PET scan?
You can expect the following during a PET scan:
- You’ll receive an IV injection of a radiotracer that contains a
safe amount of a radioactive drug. The most commonly used
radiotracer is fluorodeoxyglucose (FDG).
- You’ll sit in a chair for about an hour while the radiotracer
moves through your bloodstream and gets absorbed by your organs
and tissues. Too much activity can send the radiotracer to areas
of your body that your healthcare provider isn’t testing. You
won’t be able to feel the radiotracer.
- If you’re getting a PET/CT scan, you may also get an IV
injection of a contrast dye. This dye helps produce sharper CT
images.
- You’ll lie on an exam table that slides in and out of the PET/CT
scanner. This scanner is shaped like a doughnut. The doughnut or
tunnel opening is about 30 inches in diameter.
- During the scan, which usually takes about 30 minutes, you must
remain still. Movement can blur the images.
- You’ll hear buzzing and clicking sounds as the scanner takes
images.
- A technologist will review the scans before you leave to ensure
the images are in focus.
How long does a PET scan take?
The entire PET scan process takes about two hours.
It can take up to 60 minutes for your body to absorb the injected
radiotracer. During this time, you’ll need to sit quietly and limit
your movements. The actual PET scan takes about 30 minutes. After
the test, you’ll need to wait while the technologist reviews the
scans to ensure the images are clear.
What will I experience during and after the procedure?
Except for intravenous injections, most nuclear medicine procedures are
painless. Reports of significant discomfort or side effects are rare.
You will feel a slight pin prick when the technologist inserts the
needle into your vein for the intravenous line. You may feel a cold
sensation moving up your arm during the radiotracer injection.
Generally, there are no other side effects.
PET scans only use radiotracer injections.
With some procedures, the
technologist may place a catheter into
your bladder. This may cause temporary discomfort.
It is important to remain still during the exam. Nuclear imaging causes
no pain. However, having to remain still or in one position for long
periods may cause discomfort.
If you have a fear of closed spaces, you may feel anxious during the
exam.
Unless your doctor tells you otherwise, you may resume your normal
activities after your exam. A technologist, nurse, or doctor will
provide you with any necessary special instructions before you leave.
The small amount of radiotracer in your body will lose its radioactivity
over time through the natural process of radioactive decay. It may also
pass out of your body through your urine or stool during the first few
hours or days after the test. Drink plenty of water to help flush the
material out of your body.
Results
A specialist trained to interpret scan images, called a radiologist,
will report the findings to your provider. This process usually takes 24
hours.
The radiologist may compare your PET images
with images from other tests you've undergone recently, such as an MRI or CT.
Or the PET images
may be combined to provide more detail about your condition. Normal Results
A normal result means there were no problems seen in the
size, shape, or position of an organ. There are no areas in
which the tracer has abnormally collected.
What Abnormal Results Mean
Abnormal results depend on the part of the body
being studied. Abnormal results may be due to:
- Cancer
- Infection
- Problem with organ function
Benefits vs.
Risks
Benefits
- Nuclear medicine exams provide unique information that is often
unattainable using other imaging procedures. This information may
include details on the function and anatomy of body structures.
- Nuclear medicine supplies the most useful diagnostic or treatment
information for many diseases.
- A nuclear medicine scan is less expensive and may yield more precise
information than exploratory surgery.
- By identifying changes in the body at the cellular level, PET
imaging may detect the early onset of disease before it is evident
on other imaging tests such as CT or MRI.
The benefits
of a combined PET/CT scan include:
- greater detail with a higher level of accuracy; because both scans
are performed at the same time without the patient having to change
positions, there is less room for error.
- greater convenience for the patient who undergoes CT and PET at one
time rather than two different times.
Risks
- Because nuclear medicine exams use only a small dose of radiotracer,
they have a relatively low radiation exposure. This is acceptable
for diagnostic exams. Thus, the potential benefits of an exam
outweigh the very low radiation risk.
- Doctors have been using nuclear medicine diagnostic procedures for
more than six decades. There are no known long-term adverse effects
from such low-dose exposure.
- Your doctor always weighs the benefits of nuclear medicine treatment
against any risks. Your doctor will discuss the significant risks
prior to treatment and give you an opportunity to ask questions.
- Allergic reactions to radiotracers are extremely rare and usually
mild. Always tell the nuclear medicine personnel about any allergies
you may have. Describe any problems you may have had during previous
nuclear medicine exams.
- The radiotracer injection may cause slight pain and redness. This
should rapidly resolve.
- Women should always tell their doctor and radiology technologist if
there is any possibility that they are pregnant, or they are
breastfeeding.
Considerations
Nuclear medicine procedures can be time consuming. It can
take several hours to days for the radiotracer to accumulate
in the area of interest. Plus, imaging may take up to
several hours to perform. In some cases, newer equipment can
substantially shorten the procedure time.
The image resolution of nuclear medicine images may not be
as high as that of CT or MRI. However, nuclear medicine
scans are more sensitive for a variety of indications. The
functional information they yield is often unobtainable
using other imaging techniques.
Altered blood sugar or blood insulin levels may adversely
affect the test results of diabetic patients or patients who
have eaten a few hours prior to the exam.
The radiotracer decays quickly and is effective for only a
short time. Therefore, it is important for you to be on time
for your appointment and to receive the radioactive material
at the scheduled time. Late arrival for an appointment may
require you to reschedule the procedure.
A very obese person may not fit into the opening of a
conventional PET/CT unit.
Most PET scans are now performed along with a CT scan. This combination
scan is called a PET/CT. This helps find the exact location of the tumor
or other abnormality.
Research and Clinical Trials
PET scans are also big in research and trials for Alzheimer’s and other
brain diseases. Scientists use them to study these diseases, find new
treatments, and test new ideas.
They let researchers see and measure amyloid
plaques and tau
tangles in the brain. This helps them understand how these diseases
work and find better treatments. Trials use PET scans to see if new
treatments work and how patients react.
Neurological Disorder |
Role of PET Scan |
Alzheimer’s Disease |
Detects amyloid
plaques and tau
tangles for early diagnosis and monitoring progression |
Parkinson’s Disease |
Assesses dopamine function and monitors response to
treatment |
Huntington’s Disease |
Evaluates brain metabolism and tracks disease progression |
PET Scan Safety and Radiation Exposure
PET scans are safe for most patients. The main worry is the radioactive
tracers used. These tracers expose patients to low levels of radiation.
But, the benefits of the scan usually outweigh the risks of low-dose
exposure.
Doctors follow strict rules to keep radiation
safety in check during PET scans. They control the radiation amount
to keep it as low as needed. This ensures clear images without too much
radiation.
Special care is needed for pregnant
women and nursing
mothers. Pregnant
women should tell their doctor before a PET scan. The radiation
could harm the fetus. Usually, safer imaging options like ultrasound or MRI are
suggested instead.
Nursing mothers should talk to their healthcare provider too. They
might be asked to pump and store breast milk before the scan. They
should also avoid breastfeeding for a bit after to protect the baby from
radiation.
Patients can feel safe knowing the medical team is trained in radiation
safety. The equipment is kept in top shape for safe and accurate
scans. This way, healthcare providers aim to get the most from PET scans
while keeping risks low.
Advancements in PET Scan Technology
PET scanning has seen big changes in recent years. New technologies and
the need for better diagnostic tools have driven these improvements.
These changes have made PET scans more accurate and opened up new
research areas.
Hybrid imaging systems, like PET/CT and PET/MRI scanners, are key
breakthroughs. They combine PET’s metabolic info with CT or
MRI’s detailed images. This gives doctors a full view of the body’s
health, leading to better diagnoses and treatments.
Combined PET/CT and PET/MRI Scanners
PET/CT scanners are now central to molecular
imaging. They mix PET and CT images
perfectly. This helps find and understand diseases like cancer and heart
issues more clearly.
Advantage |
PET/CT |
Standalone PET or CT |
Anatomical Localization |
Precise fusion of functional and structural information |
Limited anatomical context |
Diagnostic Accuracy |
Improved specificity and reduced false positives |
Higher risk of misinterpretation |
Treatment Planning |
Enables targeted therapy and surgical guidance |
Lacks detailed anatomical information for precise planning |
PET/MRI scanners also offer great benefits. They combine PET’s metabolic
info with MRI’s detailed images. This is great for brain imaging and
certain cancers, thanks to MRI’s soft tissue contrast.
Future Developments and Research
The future of PET scans looks bright. Researchers are working to make
PET scans even better. They aim to improve how clear and accurate the
images are. Artificial intelligence and machine learning will also
change how we analyze PET images.
Personalized medicine is becoming more important, and PET scans will
play a big role. They help tailor treatments to each patient’s needs.
This could lead to better treatment results and fewer side effects.
As research advances, we can expect even more exciting changes in PET
scan technology. New tracers and the integration of PET with other
imaging methods will shape medical imaging. These developments will help
diagnose and treat diseases better, benefiting patients everywhere.
Accessing PET Scan Services
To get a PET scan, you need a referral from your doctor. This involves
checking your medical history and current health. This helps decide if a
PET scan is right for you.
After getting a referral, your doctor will write a prescription. This
prescription will say what kind of PET scan you need and any extra steps
to follow.
Looking for a place to get your PET scan? Your doctor can recommend a
good imaging center. You can also search online. Make sure the center is
accredited by groups like the American College of Radiology. This means
they follow strict quality and safety rules.
Insurance Coverage and Costs
How much insurance covers for PET scans depends on your plan and why you
need it. Most plans, including Medicare and Medicaid, cover PET scans if
they’re needed. But, you might have to pay a part of the cost, like a
copay or deductible.
Check with your insurance to know what you’ll pay. If you don’t have
insurance or it doesn’t cover much, some centers offer help. They might
have lower prices or payment plans to make it easier to pay for the
scan.
FAQ's
Q: What is a PET scan and how does it differ from other imaging
techniques?
A: A PET scan uses radioactive
tracers to see how the body works. It shows how cells
use glucose, unlike CT or MRI scans.
These scans mainly show the body’s structure, not how it
functions. Q: How do I prepare for a PET scan?
A: Before a PET scan, you might need to fast for hours and
avoid exercise. Your doctor will tell you what to do,
including any medicine changes. You’ll get a radioactive
tracer through an IV and wait for about an hour before the
scan starts. Q: How is a PET scan used in cancer detection and management?
A: PET scans help doctors understand cancer by showing
where it is and how it’s growing. They can spot cancer
before it shows up on other scans. This helps doctors
plan the best treatment for you. Q: Can PET scans help diagnose Alzheimer’s and other neurological
disorders?
A: Yes, PET scans are key in finding and tracking
Alzheimer’s and other brain diseases. They can spot amyloid
plaques and tau tangles in the brain. This helps doctors
diagnose Alzheimer’s early and track how it progresses. Q: Are PET scans safe, and how much radiation exposure is involved?
A: PET scans are mostly safe, with low radiation doses. The
benefits of getting a clear diagnosis are worth the small
risk. Pregnant and nursing women need extra care. Talk to
your doctor about any concerns. Q: How can I access PET scan services, and will my insurance cover
the costs?
A: To get a PET scan, you need a doctor’s referral. They can
find a good imaging center for you. Insurance for PET scans
varies. Check with your provider to see what’s covered and
what you might pay out of pocket.
One Final Note..
A positron emission tomography (PET) scan is a very useful and
generally safe imaging test that healthcare providers use to assess
cancer, heart issues and brain conditions. If you need a PET scan
and are worried about the exam or have questions about it, don’t be
afraid to ask your healthcare provider. They’re available to help
and support you.
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