What Imaging Tests Can Be Used to Guide Prostate Cancer Diagnosis?

Prostate cancer is the most common nonskin cancer in men. Over 300,000 cases of prostate cancer are diagnosed in the U.S. each year. In fact, approximately 1 in 8 men will be diagnosed with prostate cancer during their lifetime. Many more men probably have prostate cancer but never know it. 

In most cases, prostate cancer is diagnosed at an early stage. That means it hasn’t spread beyond the prostate gland. Fortunately, early-stage prostate cancers usually aren’t  life-threatening. But when prostate cancer spreads to other parts of the body, it’s not curable and is often fatal. About 35,000 men die from prostate cancer in the U.S. each year.

There are many tests used in the diagnosis of prostate cancer. Let’s review how prostate cancer imaging can aid in making a prostate cancer diagnosis and which imaging tests are most commonly used.

What imaging tests are used in the diagnosis of prostate cancer?

Several types of imaging are commonly used in the management and diagnosis of prostate cancer. The most common ones are:

• Magnetic resonance imaging (MRI)

• Transrectal ultrasound (TRUS)

• Bone scan, or bone scintigraphy

• Computed tomography (CT)

• Positron emission tomography (PET) scan

Let’s take a closer look at each prostate cancer imaging test below.

MRI

Magnetic resonance imaging (MRI) scans work by using a powerful magnet to generate a three-dimensional image. A prostate MRI scan produces a clear image of the prostate gland and surrounding organs. This includes pictures of tumors within the prostate gland. MRI of the prostate gland has several different uses in people with suspected or known prostate cancer. 

First, prostate MRI can help doctors decide whether someone with an elevated PSA needs a prostate biopsy. In some cases, if the PSA is elevated but the MRI looks normal, the risk of cancer may be low enough that a biopsy isn’t needed. 

Getting an MRI scan involves lying flat on a table, which moves slowly through a tube. In most cases, you will get intravenous (IV) contrast dye through a vein in your arm to improve the images. Getting the IV might cause temporary discomfort, but the scan itself is painless. A prostate MRI usually takes about 45 to 60 minutes to complete.

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MRI scanners can make loud noises, and some people feel claustrophobic while they’re inside the machine. It’s important to know that, unlike an X-ray or a CT scan, there’s no radiation exposure with an MRI scan.

TRUS

Transrectal ultrasound (TRUS) is an imaging test that’s used to identify the prostate gland during a prostate biopsy. Ultrasound works by sending out sound waves and using the echo to create an image. This mechanism is like sonar technology — often used in submarines — and the “echolocation” that dolphins and whales use to navigate in the ocean.

For prostate ultrasound, a healthcare professional will place an ultrasound probe in the rectum (hence the term “transrectal” ultrasound). Since the prostate sits right in front of the rectum, this produces a clear image of the prostate gland. Although the ultrasound probe causes some discomfort, most people tolerate it fairly well.

With the prostate clearly visible by ultrasound, the healthcare professional (usually a urologist) inserts the biopsy needles through the wall of the rectum into the prostate to gather tissue samples.

Prostate tumors aren’t visible on ultrasound like they are on MRI. So ultrasound and MRI are sometimes combined to biopsy a specific part of the prostate gland. This is called a fusion biopsy. To perform a fusion biopsy, ultrasound images and MRI images are “fused,” or layered on top of one another. The healthcare professional can then use a live ultrasound image to biopsy a tumor that’s only visible on MRI. Recent research shows improved detection of prostate cancer using this approach.

Bone scan

Bone scan, or bone scintigraphy, is an imaging test that checks the whole skeleton for metastasis, or tumor spread. When prostate cancer spreads, it most commonly goes into bone.  This is why a bone scan is such a useful test in people with prostate cancer. It’s important to note that a bone scan is not used in all cases of prostate cancer. In fact, it’s only used when a healthcare professional suspects or wants to rule out metastasis.

The first step in getting a bone scan is the injection of a radioactive tracer called technetium-99 into your vein. This tracer will build up in areas of bone metastasis, although it usually takes several hours to do so. So the scan isn’t done until a few hours after the injection.

The scan itself involves lying on a table while the scanner moves around the body. Like an MRI and a CT scan, a bone scan is painless.

CT scan

Computed tomography (CT) is an imaging test that can be used to check if prostate cancer has spread to other areas of the body, such as lymph nodes, lungs, or liver. CT scans work by using X-rays to generate a three-dimensional image of the body. Unlike MRI scans, CT scans use radiation.  

The main advantage of a CT scan is that it can be completed much more quickly than an MRI. In addition, people experience fewer issues with claustrophobia. This is because CT scanners aren’t as narrow as MRI scanners.

PSMA PET scan

A prostate-specific membrane antigen (PSMA) PET scan is a special kind of imaging test that targets prostate cancer cells. For this scan, you get a tiny bit of a radioactive chemical called a tracer. With a PSMA PET scan, the tracer is made to stick to prostate cancer cells. When the tracer sticks to these cancer cells, it gives off energy, which can be seen on the imaging test.

The PSMA PET scan is helpful for seeing how advanced the prostate cancer may be (staging), but also in looking for metastasis, and following the response to treatment. 

How is prostate cancer diagnosed?

Most people diagnosed with prostate cancer don’t have any symptoms. This is why screening for prostate cancer is so important. The most common way to screen for prostate cancer is with a blood test for PSA.

In general, your PSA level is considered “normal” if it’s less than 4 ng/mL. A PSA level higher than 4 ng/mL can be a sign of prostate cancer. But PSA can be elevated for other reasons, and you can have a normal PSA level and still have prostate cancer. So a PSA test alone can’t confirm prostate cancer.

If your PSA level is elevated, a healthcare professional may recommend a prostate biopsy. This involves taking a tissue sample of the prostate, usually with a needle. A biopsy is necessary to confirm a prostate cancer diagnosis in most cases.

If a prostate biopsy shows cancer, a pathologist will classify the cancer cells according to how different they look from normal cells. This is called the tumor grade, or the Gleason score. In some cases, additional tests may be done on the DNA, or genetic material, of the cancer cells.

When do you need imaging for prostate cancer?

Until recently, it was common for almost all people with elevated PSA to get a prostate biopsy.  But we now know that some people with an elevated PSA don’t need a biopsy. In these situations, imaging can help make a diagnosis.

Imaging tests can also help answer questions that come up in people who have (or might have) prostate cancer. Some of these questions include:

• Does this person need a prostate biopsy?

• What part of the prostate gland should be biopsied?

• What’s the prostate cancer stage?

• What’s the best treatment for this person’s prostate cancer?

• How has this person responded to prostate cancer treatment?

• Has this person’s prostate cancer come back after treatment?

It’s important to note that imaging is not required in every case of prostate cancer. In many cases, treatment decisions can be made without imaging.

What is the most accurate imaging test for a prostate cancer diagnosis?

There’s no single imaging test that’s right for every person with prostate cancer. In other words, prostate cancer imaging isn’t one-size-fits-all. In fact, the best imaging test for a person will depend on multiple factors, such as the PSA level, the Gleason score, and the kinds of treatment being considered.  

How to prepare for prostate cancer imaging

When a healthcare professional orders an imaging test, you will probably get instructions on how to prepare for the tests. It’s important to follow those instructions. Here is a brief overview of things to know as you prepare for the different prostate cancer imaging tests.

MRI

MRI is safe for most people. But if you have metallic implants (like surgical screws or plates), it may not be safe to have an MRI scan. MRI may affect the function of some pacemakers, defibrillators, or other implanted devices. So if you have any metal or an implanted device in your body, be sure to ask your healthcare team if it’s safe to get an MRI.

Additionally, MRI often involves the use of an IV contrast called gadolinium. Although this contrast is usually safe, some people can have allergic reactions to gadolinium. Be sure to let your healthcare team know if you’ve had an allergy to contrast before. People with chronic kidney disease may also need to avoid gadolinium because it can damage their kidneys.

Finally, prostate MRI also sometimes involves placement of an endorectal coil. This is a wire that’s placed in the rectum to improve the quality of the images. If an endorectal coil is used, your healthcare team may instruct you to use an enema to empty your rectum before the MRI scan.

CT scan

Like MRI scans, some CT scans are done with IV contrast to make the images clearer. The most common IV contrast used for CT contains iodine. If you’re allergic to iodine, you should avoid IV contrast for CT scans.

Like gadolinium, iodine contrast can also cause problems in people who have kidney disease. So if you’re getting a CT scan with IV contrast, your doctor may order a blood test beforehand to make sure your kidneys are healthy.

Bone scan

If you’re getting a bone scan, there are no specific procedures that you need to follow before the scan. Eating and/or drinking will not affect the results of the scan.  

PET scan

Before getting a PET scan, you’ll be instructed not to eat or drink anything for several hours.  Additionally, you may need a blood test before the scan to make sure that it will be accurate.

In particular, high or low blood sugar (glucose) affects the quality of some PET scans. To ensure a high-quality scan, healthcare professionals often recommend checking a blood glucose level before the test.

Medications that change blood glucose levels can also affect PET scan results. You should tell your healthcare team about all medications that you’re taking. In some cases, they might ask you to pause taking one or more of your medications before the scan.

Frequently asked questions

More information and resources

If you or a loved one has prostate cancer, there are resources available to help you understand the condition, treatment options, and to find support:

• Radiologyinfo.org 

• National Comprehensive Cancer Network 

• American Cancer Society

• National Cancer Institute

Why trust our experts?

Written by:

David Marcus, MD

David Marcus, MD, is a board-certified radiation oncologist with expertise in the management of many types of cancer, including prostate cancer, breast cancer, and several others. He earned his medical degree at Emory University in Atlanta, Georgia, where he also completed residency training in radiation oncology.

Edited by:

Karla Robinson, MD

Karla Robinson, MD, is a medical editor for GoodRx. She is a licensed, board-certified family physician with almost 20 years of experience in health through varied clinical, administrative, and educational roles.

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