How to Read a PET Scan Report: Decoding Common Terminology

When your medical provider recommends a PET scan, it’s natural to be curious about the results. However, the technical jargon and complex medical terminology in PET scan reports can be overwhelming. This guide demystifies common terms, including acronyms, viewing planes, uptake values, and lesions, making it easier for you to understand your report.    

While understanding these terms is valuable, it’s not a replacement for your doctor’s expert interpretation. Most providers will review your results with you during a follow-up appointment or phone call. By familiarizing yourself with your report beforehand, you can engage in a more informed conversation and prepare insightful questions. PocketHealth empowers you to do this by providing secure and easy access to your imaging results as soon as they’re available.   

 

What is a PET scan?

PET is short for positron emission tomography. PET scans are considered nuclear medicine procedures because they use a radioactive substance to create images of your organs and tissues. After the radiotracer is absorbed in your body, it emits positrons that are recorded by sensitive cameras as you move through the donut-shaped array. The recordings are then compiled into colorful images for the radiologist to interpret.

Often used in conjunction with other imaging tests, like CT scans or MRIs, PET scans can assess both the function and structure of organs and tissues.

What are axial, sagittal and coronal planes?

PET scanners capture images along 3 different planes to provide the radiologist with a 360° view of your body’s internal structures and organs:

• Axial: Also called the transverse view, this horizontal view creates images of the top and bottom halves of your body.
• Sagittal: The side view, which provides lateral images of the left and right halves of the body.
• Coronal: The face-on view, which creates images of the front and back halves of your body.

What is a radiotracer?

The radioactive sugar substance used in PET scans is called a radiotracer. Injected, inhaled or ingested, the radiotracer travels through your body and gathers in cells that require a lot of energy. Fluorodeoxyglucose (FDG) is a common radiotracer.

Your PET scan report will indicate which radiotracer was used and how much was administered, at what site and by which method.

What do FDG and FDG uptake mean on a PET scan?

FDG is an abbreviation for Fluorodeoxyglucose, a widely used radiotracer that helps visualize how your body’s cells metabolize glucose. Understanding FDG and its role in PET scans is key to interpreting your imaging results. When you hear terms like “FDG uptake” or “FDG activity,” they refer to the way cells absorb and use this tracer, providing insight into your metabolic health.

What is FDG uptake?

FDG uptake describes how much radiotracer was ‘taken up’ by cells. Different cell types have unique metabolic needs, so FDG will cluster at varying concentrations in different areas of the body.

FDG activity refers to how vigorously the body’s tissues are utilizing glucose, which is reflected by how much FDG is absorbed. Higher FDG activity usually indicates higher metabolic activity. Simply put, FDG uptake is a measurement of how much FDG is in the tissues whereas FDG activity indicates the metabolic qualities that cause the absorption of FDG. Now that you have a basic understanding of FDG, here are some explanations of common terms found in PET reports.

What does no uptake mean?

No uptake means the FDG isn’t being absorbed. Whether this is a positive or problematic result depends on the baselines of the tissue being studied. For some areas, low metabolic activity is normal, in others it is a sign of an abnormality. Your doctor will weigh this result against specific tissue types, your overall medical condition and if this is normal for your baseline. Here are some possible indications: 

• Tumor or growth is not active: For areas that previously had growths or tumors, no uptake could indicate that the growth is no longer as metabolically active. This might suggest that the tissue is necrotic (dying), but it could also mean that medical treatments have been successful and the tumor or growth is no longer growing or active. Your doctor will likely confirm the results with additional testing.
• Normal tissue: Certain tissues and areas of the body are expected to have no FDG uptake or low metabolic activity. In those circumstances, this is considered a healthy result.
• Detection problems: If the scanning machine isn’t sensitive enough or is having technical issues, it may not be able to detect the FDG uptake.
• Not currently inflamed/infected: If the PET scan was to assess an area of the body with infection or inflammation, no FDG uptake could suggest that the problem has been resolved or is not currently active.

What does normal FDG uptake mean?

Areas of your body, such as the spleen, liver, and brain, tend to have higher FDG uptake because they have higher glucose needs and are therefore more metabolically active. Most tissues have established medical baselines for expected FDG absorption, which vary depending on tissue type and location within the body. Normal uptake results suggest that your tissues are functioning within expected metabolic parameters.

What does mild or low FDG uptake mean?

Low or mild FDG uptake can be normal for less active tissues or those high in fat. In some reports, it may also be referred to as low-level or low-grade FDG uptake. However, in areas expected to be more metabolically active, it may indicate the need for closer inspection. Here are some possible explanations for low FDG uptake:

• Less active or non-viable tissue: This could suggest that previously active areas are now necrotic. It might also indicate that a tumor, inflammation, or disease is less active or no longer active, which could be a positive sign of successful treatment. Your doctor will likely perform additional tests to clarify the situation.
• Possible tumor detection: Certain tumors or other conditions may naturally exhibit lower FDG uptake.
• Technical limitations or issues with the scanning equipment: Sometimes, the scanning equipment itself may have sensitivity issues or be malfunctioning, affecting the results.

What does increased FDG uptake mean?

“Increased FDG uptake” or “Intense FDG uptake” on a PET scan means that cells in a certain area of the body are absorbing more of the radiotracer FDG than surrounding tissues. This higher uptake typically appears as brighter or more intense spots on the scan. Increased FDG uptake can indicate:

• Cancer: Cancer cells are usually more active and consume more glucose, resulting in higher FDG uptake.
• Inflammation or Infection: Areas with active inflammation or infection show increased uptake due to heightened immune activity.
• Tissue Healing: Following surgery, injury, or radiation therapy, healing tissues may exhibit increased FDG uptake.
• Benign Conditions: Some non-cancerous growths or active thyroid nodules can also show higher FDG uptake.

While increased FDG uptake often raises concerns for cancer, it can also be due to benign or non-malignant processes. Proper interpretation by a radiologist, considering the clinical context and additional tests, is essential for accurate diagnosis.

What does abnormal FDG uptake mean?

This occurs when glucose absorption is at an irregular level for the tissue being assessed. This can mean either less than expected FDG absorption or higher than expected absorption. For higher FDG uptake, additional testing will typically be conducted to determine the cause. Possible indications for higher FDG uptake levels include:

• Possible cancer: Many types of cancer cells have higher metabolic activity, which leads to a higher FDG absorption rate.
• Infection or inflammation: Increased metabolic activity of immune cells responding to inflammation or infection can also result in higher FDG uptake.

What is SUV?

SUV is a medical abbreviation for the term Standard uptake value, a ratio that defines the activity of the radiotracer (such as FDG) in a specific area of a PET scan image at a specific point in time. It is also known as the dose uptake ratio.

A higher SUV may indicate increased metabolic activity, which could be due to various factors, including inflammation, infection, or cancerous growths. Conversely, a lower SUV could indicate less metabolic activity. Generally speaking, metabolic activity is considered:

• “Low intensity” at <5 SUV
• “Moderate” at 5-10 SUV
• “Intense” at 10-15 SUV
• “Very intense” at >15 SUV

The SUV value is helpful for interpretation purposes, especially when comparing multiple PET or other scans over time. The increase or decrease in SUV can give the radiologist a clear understanding of how conditions or treatments are progressing.

 

What does physiologic uptake mean on a PET scan?

The term “physiological uptake” can be confusing, as it’s conceptually similar to FDG uptake. The difference is that physiological uptake is based on the typical, expected absorption of any radiotracer throughout the body. It doesn’t have to be FDG specifically, though PET scans generally use FDG as their radiotracer of choice. The key point to understand is that different organs and tissues have different standardized expectations for radiotracer uptake because metabolic activity differs by organ or tissue type.

Knowing the standard benchmarks for physiological uptake allows physicians to determine if tissues and organs are behaving in a healthy, expected manner. Abnormalities or atypical reactions to radiotracer in these areas may suggest disease, growths or other health conditions.

Does physiological uptake mean cancer?

No, physiological uptake does not mean cancer. Physiological uptake refers to the normal absorption or accumulation of a substance, such as a contrast agent or radiotracer, in the body’s tissues during imaging studies like PET scans. This uptake occurs in organs and tissues that naturally use or process the substance, such as the brain, heart, liver, or kidneys.

While increased uptake in certain areas can sometimes indicate cancer or other abnormalities, physiological uptake is considered a normal finding and not indicative of disease. It’s important to differentiate between physiological and abnormal uptake when interpreting imaging results, and this is typically done by a radiologist or nuclear medicine specialist.

What does physiological activity in liver mean?

“Physiologic activity in the liver” refers to normal metabolic activity within the liver. This is expected because the liver is a metabolically active organ that plays a key role in various bodily functions, including glucose metabolism, detoxification, and protein synthesis. Here is what the general findings mean:

• Normal Finding: The liver naturally absorbs the radiotracer (FDG) due to its high metabolic activity. This is seen as a uniform or mildly increased uptake on the scan.
• Non-Specific: Physiologic activity does not indicate any pathology. It simply reflects the liver’s normal functioning.
• Variations: Levels of uptake can vary slightly based on factors like diet, blood sugar levels, and liver health but are generally within a normal range.

As mentioned previously, physiologic activity in the liver on a PET scan is a standard finding and is not associated with any disease.

What does physiological activity in kidneys and bladder mean?

Physiologic uptake in the kidneys and bladder refers to the normal absorption and accumulation of the radiotracer used during the scan.

• Kidneys: After the radiotracer is injected into the bloodstream, it is filtered out by the kidneys as part of the body’s natural process of removing waste. This filtering process results in the normal, or physiologic, uptake of the radiotracer in the kidneys, which will show up on the PET scan.
• Bladder: As the kidneys filter the radiotracer, it is excreted into the urine and accumulates in the bladder. The bladder then shows physiologic uptake as it stores this radiotracer, which is also visible on the PET scan.

This physiologic uptake is expected and indicates that the kidneys and bladder are functioning properly in filtering and excreting the radiotracer. It is not a sign of disease but rather a normal part of the body’s response during the PET scan.

What does metabolic activity mean on a PET scan?

Metabolic activity on a PET scan refers to how actively cells in the body are using glucose or other metabolic substrates. PET scans detect this activity by using a radiotracer, like FDG, which highlights areas with increased metabolic uptake, helping to identify abnormal or potentially diseased tissue.

What does no metabolic activity mean on a PET scan?

No metabolic activity can have various implications on a PET scan. In certain areas of the body, this may be expected if the tissues don’t normally react to glucose or metabolic factors, which is a normal result. However, if this result is seen as an abnormality, it could suggest the following possibilities:

• Damaged Tissue: The tissue could be necrotic or damaged to the extent that it no longer metabolizes FDG effectively.
• Possible Blockages: There may be reduced blood flow or other blockages, such as those resulting from heart attacks or strokes, affecting the area.
• Possible Successful Treatment: In the context of a tumor or growth, a lack of metabolic activity could indicate that the abnormality is no longer active, suggesting a positive response to treatment and potential improvement in health.

What does low-grade or mild metabolic activity mean?

Low-grade metabolic activity (also called mild metabolic activity) means that less radiotracer is being absorbed. For certain tissues and organs, this may be a normal result due to inherently lower metabolic activity. However, when low-grade metabolic activity is observed as an abnormality, it can be indicative of several conditions:

• Early Stages of Infections or Disease: This might represent the initial phase of conditions such as tumors or infections, where metabolic activity has not yet increased and remains low-grade.
• Scar Tissue: Fibrous tissues resulting from previous surgeries or injuries generally have lower metabolic demands compared to healthy or diseased tissues.
• Aging: Metabolic rate naturally declines with age, so low-grade metabolic activity in older adults can be a normal and expected finding.
• Metabolic Disorders: Certain metabolic disorders can impact metabolic activity and radiotracer uptake. Examples include diabetes, metabolic syndrome, enzyme deficiencies, hypothyroidism and similar conditions.
• Beginning of Successful Treatment/Healing: As tumors, inflammation, or diseases respond to treatment, a reduction in metabolic activity may indicate that healing or treatment efficacy is occurring.

What does increased metabolic activity or hypermetabolic mean?

Increased metabolic activity also called hypermetabolic often indicates that cells are more active than normal, which can be a sign of inflammation, infection, or cancer, as these cells tend to consume more glucose.

“Increased metabolic activity” or “hypermetabolic” on a PET scan indicates areas where cells are more active than normal and tend to consume more glucose. These areas show an increased radiotracer uptake and appear as brighter spots on the scan.

Increased metabolic activity may indicate:

• Cancerous Tumors: Rapidly dividing cancer cells consume more glucose.
• Inflammation and Infection: Active immune responses increase cellular activity.
• Healing and Tissue Repair: Regenerating tissues post-injury or surgery show temporary increases.
• Benign Conditions: Some non-cancerous conditions, such as benign tumors, may also appear hypermetabolic.

While increased metabolic activity can signal serious conditions, it is not always indicative of cancer. A radiologist and doctor will interpret these results based on your medical history and further testing.

What’s a Deauville Score?

The Deauville score or scale (DS) is an internationally recommended standard for reporting FDG uptake in treatment trials for Hodgkin’s and non-Hodgkin’s lymphomas. Like the SUV, it measures FDG uptake, but the Deauville score is a visual interpretation that compares uptake in affected areas to uptake in the liver and mediastinum (the space between the lungs containing the esophagus, heart, large blood vessels and trachea).

The Deauville score runs from 1 to 5:

1. No uptake
2. Slight uptake, equal or below uptake in the mediastinum
3. Uptake above the mediastinum but below the liver
4. Uptake slightly or moderately above the liver
5. Noticeably increased uptake compared to the liver

When it comes to the Deauville score, a lower number is better. 1 and 2 are both considered complete responses. 3 is adequate, while 4 and 5 are considered inadequate.

 

Is unremarkable good or bad?

In medical terminology, “unremarkable” is a good thing: it means your PET scan reports no abnormal findings. Your PET scan report is one place you actually want to be found unremarkable.

How PocketHealth Report Reader can help you understand your PET scan report

PocketHealth gives you fast and easy access to view, share and store your PET scan results, often before your follow-up appointment with your doctor.

If you are unfamiliar with certain medical terms, Report Reader will provide definitions to help make your report easier to understand.

“With Report Reader, I get explanations for words [in my report] that I don’t understand. I can now discuss my health with my family doctor with more confidence and have a better understanding of what is going on.”
– Amy J.

The importance of understanding your PET scan results

PET scan images reveal the inner structures of your body and how well they are functioning, making it a valuable tool when it comes to diagnosing or monitoring the treatment of many diseases. For Jeanne, a breast cancer survivor, PocketHealth became a lifeline during her time abroad in Costa Rica. With easy access to all her previous imaging, she was able to get treatment for hip, back, and knee pain from a new doctor who could review her past scans instantly. This ability to access her medical history from anywhere ensured she received the care she needed, even thousands of miles from home.

The more you understand what’s going on in your body, the more thorough your medical follow-up conversations can be. Having access to your PET scan results gives you the information you need to ask more pertinent questions and make more informed choices. PocketHealth makes that access easy and secure, so you can be confident and in control along every step of your healthcare journey.