Positron emission tomography (PET) is a type of imaging scan that doctors might use when diagnosing and treating non-Hodgkin’s lymphoma (NHL). It can be useful for identifying and staging the cancer.

Non-Hodgkin’s lymphoma (NHL) is a cancer of the lymph nodes. These are small structures in the neck, armpits, chest, abdomen, and groin. They usually form part of the immune system, helping to send white blood cells around the body and counter infections.

Positron emission tomography (PET) scans can play a significant role in diagnosing NHL. This article explains how they work for people with NHL and what to expect during a PET scan.

A person is getting a PET scan.Share on Pinterest
andresr/Getty Images

Doctors may use a PET scan along with other diagnostic tests to diagnose NHL.

If an individual notices that they have a swollen lymph node, a doctor may request a PET scan to check whether the swelling shows cancerous activity.

PET scans can also show whether an already confirmed NHL diagnosis is responding to treatment.

A PET scan might also be able to show whether a swollen lymph gland contains lymphoma or mainly consists of scar tissue after surgery.

Doctors may use PET scans for staging NHL. The scan can highlight areas of lymphoma that have appeared in different nodes and help determine how aggressive they are.

During staging, a clinician determines how aggressive a cancer is, including whether it has invaded deeper tissues or spread to other organs.

PET scans may also support other methods of staging, such as biopsies, by finding areas that are accessible for a biopsy. Biopsies are the only way to confirm NHL.

Learn about NHL stages.

PET is a scan that uses a tracer to show tumor activity. Research published in 2017 indicates that lymphoma cells are particularly responsive to a tracer called fluorodeoxyglucose (FDG).

A tracer is a radioactive substance containing a form of sugar that cancer cells, such as lymphoma, take up much more readily than healthy tissue does.

By tracking how lymphoma cells absorb FDG, PET can show where lymphoma is active and how aggressive it is.

Some machines provide PET and computed tomography (CT) scans at the same time. These can combine the detailed imaging of a CT scan with the tracking of radioactivity from the PET scan.

According to the United Kingdom’s National Health Service (NHS), the doctor injects the tracer into a person’s hand or arm around 60 minutes before the scan to allow enough time for the tracer to move around the body.

The scan involves lying on a flat bed that moves into a tube-shaped, body-sized scanner. The scanner creates images for 30 to 60 minutes, during which time a person should remain as still as possible and avoid talking.

The medical team will be able to communicate what is happening during the scan.

The Dana-Farber Cancer Institute reports that a person may need to avoid eating or drinking anything other than plain water around 6 hours before the scan.

They should also avoid any exercise or strenuous activity 24 hours before the scan.

An individual should wear loose, comfortable clothes during a PET scan and avoid wearing jewelry on the day. They should also avoid clothing with zippers, buttons, and other metal parts.

A person can talk with their doctor about medications they may be able to take to ease anxiety during the scan.

People can usually leave the clinic on the same day as a PET scan, as it is unlikely to cause adverse effects.

However, the results will not be available on the same day. They will usually be ready within a couple of weeks, per Cancer Research UK.

Drinking plenty of fluids after the scan can help flush the tracer from the body and reduce exposure to radiation.

People should try to avoid spending time around pregnant people, infants, and young children for several hours after the scan, as it is possible to expose others to radioactive materials immediately afterward.

Tracer injections are radioactive, which carries a very small risk of causing tissue damage or further cancers at a later date.

A PET/CT scan can expose a person to further radiation during the CT part of the scan. However, the risk of this is also extremely low.

Here are some frequently asked questions about NHL and PET scans.

What is the best test for non-Hodgkin’s lymphoma?

Several tests often play a role in diagnosing NHL. However, a biopsy is the only way to confirm an NHL diagnosis.

Do cancerous lymph nodes show up on PET scan?

Cancerous lymph nodes show on a PET scan. A scan can show whether enlarged lymph nodes contain NHL or other cancers.

What imaging is used for non-Hodgkin’s lymphoma?

Along with PET scans, a doctor may request an ultrasound to check for enlarged lymph nodes inside the body or to examine lymph nodes close to the skin’s surface. Chest X-rays and CT scans may also help.

If a doctor suspects that NHL has spread to the bones or brain, they may request a bone scan or MRI.

What cancers cannot be detected by PET scan?

According to a 2006 review, PET scans may miss some tumors that do not process as much glucose as others, such as:

  • low grade lymphomas
  • adenomas
  • bronchioloalveolar carcinomas
  • carcinoid tumors
  • small tumors

Whether a doctor requests a PET scan can depend on the type of cancer they suspect. A person’s doctor can provide more information about whether they recommend PET scans or other imaging tests.

Positron emission tomography (PET) scans can help doctors identify lymph nodes that show non-Hodgkin’s lymphoma (NHL) activity.

They can help guide cancer care teams to accessible or high risk areas ahead of biopsies. The scan can also show whether treatment is having the desired effect on NHL.

During a PET scan, a healthcare professional injects a radioactive tracer that shows on an image. Cancers consume more of this tracer than healthy cells.

The doctor will advise how long a person should avoid eating or exercising before the procedure. They can also provide more information about what a person can expect during and after the scan.