SUMMARY
PET/MRI imaging for prostate cancer is superior to PET/CT because it offers excellent anatomic definition and tissue characteristics but with less exposure to radiation. It is most helpful in cases of suspected aggressive cancer, complex disease, and recurrence after local treatment. It can also help avoid an unnecessary biopsy.
What is PET/MRI for prostate cancer?
PET/MRI is a combination method of imaging prostate cancer that not only detects clinically significant tumors in the prostate but also reveals if the cancer has spread to lymph nodes or bones. Each type of imaging has its own unique strength.
PET stands for Positron Emission Tomography, which highlights tissues like cancer because of its high metabolic activity (high energy use by rapidly growing cancer cells. It uses a substance called a radiotracer (or simply tracer) that is injected into the bloodstream and “settles” in cancer cells. This tracer “lights up” during the scan, revealing cancer locations.
MRI stands for Magnetic Resonance Imaging, which gives a detailed portrait of pelvic tissue anatomy. It shows the prostate gland with its internal zones, suspicious tumor shapes and locations, and nearby soft tissue and bone structures, in high resolution detail.
Why combined PET with MRI in the same scanning session?
Since each imaging method has its own particular strength, combining them during the same imaging session not only shows suspicious locations as seen on multiparametric MRI (mpMRI), but also characterizes them as cancer if they “light up” when the tracer is injected into a vein.
When the two methods are used together, the combination is abbreviated as PET/MRI. This dual type of imaging shows more than either single imaging alone, especially when significant prostate cancer is suspected, or cancer that has spread to nearby lymph nodes, neighboring tissues, and bone.
Until the introduction of PET/MRI, the imaging that was used for suspected advanced prostate cancer was PET/CT. PET/CT stands for combined PET with CT (Computed Tomography). However, PET/MRI has more advantages than PET/CT.
What advantages does PET/MRI have that PET/CT does not?
PET/MRI has two main advantages over PET/CT.
- mpMRI offers better details of soft tissue anatomy than CT. While both use the PET imaging component called radiotracers (or simply tracers), seeing clearer anatomic details allows better location of cancerous sites. This is important for staging the precise extent of cancer.
- CT involves radiation to depict soft tissue, whereas MRI does not. In fact, a 2025 article in the Journal of the American Medical Association reports that repeated exposure to CT radiation raises the risk of developing cancer more than was previously thought.[i]
Although PET/MRI is newer than PET/CT, more imaging centers are starting to offer PET/MRI for suspected advanced prostate cancer.
What is the best use for PET/MRI?
While mpMRI is the gold standard for imaging lower risk or localized prostate cancer, PET/MRI is best used if there is suspicion of higher risk disease or complex cases in which cancer may have begun to spread beyond the prostate capsule. Such suspicion is often raised by a high PSA blood test result, or a high Gleason grade or Grade Group result from a biopsy.
It is also particularly valuable if cancer recurrence is suspected after treatment for localized prostate cancer. As is sometimes the case, at the time of surgery or radiation for localized disease some previously undetected microscopic cancer is left untreated in neighboring tissues where it can continue to grow. A rise in PSA is usually the first sign that cancer may be back.
Therefore, according to Regmi, et al. (2021), “The importance of [combined] multiparametric MRI (mpMRI) and PET based imaging for the diagnosis and staging of prostate cancer cannot be understated.”[ii]
How is the information from PET/MRI helpful?
Since PET/MRI is more advantageous than PET/CT for characterizing the extent of prostate cancer (staging), it provides excellent help for planning treatment tailored to each patient.
If a patient is diagnosed with prostate cancer that has advanced beyond the capsule, or has come back after primary treatment, there are many strategies for controlling the further progression of prostate cancer for many years. These include androgen deprivation therapy (ADT or hormone therapy), salvage radiation, immunotherapy drugs, post-radiation ablation or surgery to debulk the local tumor, etc.
Finally, if PET/MRI does not reveal probable cancer, in many cases a biopsy can be avoided.
Conclusion
In conclusion, PET/MRI outperforms PET/CT for detecting aggressive, advanced prostate cancer that has spread beyond the prostate gland. This enables more effective treatment planning for each patient, in order to extend life. If no suspicious cancer is seen, a biopsy may be avoided.
Frequently asked questions
Q: How does multiparametric MRI (mpMRI) work to show prostate anatomy?
A: mpMRI integrates at least three imaging sequences to show various characteristics of prostate tissue. In addition to detailed prostate anatomy, it can reveal abnormally dense tissues (probable cancer), and unusual tumor blood flow (another indication of probable cancer).
Q: If mpMRI shows an area suspicious for significant prostate cancer, what does PET add?
A: Combining PET with MRI adds further confirmation that prostate cancer is present. The tracer used in PET imaging is bonded with a molecule that cancer cells “take up.” It then “lights up” during the imaging session, but the radiation quickly dies off and the tracer is washed out of the patient’s body.
Q: Doesn’t the tracer expose the patient to radiation?
A: According Prof. Thomas Hope, MD, “The PET/MRI has the best PET detectors in modern imaging. That means we are able to use a lower dose of injected radiotracers… With PET/MRI, there is no CT component, so there’s no radiation. Instead of using radiation to make an image, the MRI uses varying magnetic fields.”
Content reviewed by Dr. Dan Sperling, M.D., DABR — updated December 2025.
NOTE: This content is solely for purposes of information and does not substitute for diagnostic or medical advice. Talk to your doctor if you are experiencing pelvic pain, or have any other health concerns or questions of a personal medical nature.
References
[i] Anderer S. CT Scans Linked to More Cancer Cases Than Previously Estimated. JAMA. 2025 Jun 17;333(23):2043.
[ii] Regmi SK, Sathianathen N, Stout TE, Konety BR. MRI/PET Imaging in elevated PSA and localized prostate cancer: a narrative review. Transl Androl Urol. 2021 Jul;10(7):3117-3129.
About Dr. Dan Sperling
Dan Sperling, MD, DABR, is a board certified radiologist who is globally recognized as a leader in multiparametric MRI for the detection and diagnosis of a range of disease conditions. As Medical Director of the Sperling Prostate Center, Sperling Medical Group and Sperling Neurosurgery Associates, he and his team are on the leading edge of significant change in medical practice. He is the co-author of the new patient book Redefining Prostate Cancer, and is a contributing author on over 25 published studies. For more information, contact the Sperling Prostate Center.
