Prostate MRI: What You Should Know

Andrew Siegel MD  5/18/2019

MRI (magnetic resonance imaging) is a high-resolution test that is an important tool for prostate cancer diagnosis, targeting of biopsies, clinical staging, surgical planning, follow-up of prostate cancer patients managed with active surveillance and in the evaluation of recurrent prostate cancer following treatment. A shout-out to Dr. Robert Waxman, who provided the MRI images seen below. 

MRI uses a powerful magnet to enable viewing of the prostate gland and surrounding tissues in multiple planes of view with the advantage of not requiring radiation. The planes are axial (cross section), sagittal (the plane that divides the body into left and right) and coronal (a plane dividing the body into dorsal and ventral parts). The axial images are by far the most important images of the study. MRI identifies areas suspicious for cancer and enables “targeted” biopsies as opposed tosystematic” biopsies. Although useful in the diagnostic evaluation of any man who has a suspicion of prostate cancer, it is particularly beneficial in men who have had previous benign prostate biopsies who have persistent PSA elevations or accelerations.

MRI is a valuable part of the diagnostic armamentarium, increasing the detection rate of clinically significant (Gleason score 7 or higher) prostate cancers, while reducing the detection rate of clinically insignificant (Gleason score 6) cancers. MRI provides anatomical details about the neuro-vascular (nerve and blood vessel) bundles, urinary bladder, seminal vesicles, pelvic lymph nodes, bowel and pelvic bones and beneficial staging information on tumor extension beyond the prostate capsule, pelvic lymph node enlargement and seminal vesicle involvement.

Prostate MRI is performed at specialty imaging centers.  Preparation involves a Fleet enema to clear gas from the rectum that can generate artifacts on the MRI images making interpretation suboptimal.  A coil placed in the rectum (endo-rectal coil) is no longer necessary as it was in prior versions of MRI. The study is done before and after the injection of about 20 cc of intravenous contrast to optimize the results.

Note: MRI cannot be performed under the following circumstances: pacemaker, recent coronary artery stent placement, ferromagnetic brain aneurysm clips and the presence of metal near the spinal cord, e.g., bullet fragments.

Refinements in MRI involve diffusion and perfusion studies. Diffusion is the movement of water into tissues; because prostate cancer cells are more tightly packed than normal cells, diffusion is often restricted with prostate cancers. Perfusion is the circulation of blood to tissues; because prostate cancers are hyper-vascular (increased blood supply), with the injection of the intravenous contrast there is increased perfusion with prostate cancers.

The value of prostate MRI is highly operator-dependent and requires both a quality study and interpretation by a skilled and experienced radiologist. Sophisticated software performs image analysis, assisting radiologists in interpreting and scoring MRI results. A validated scoring system known as PI-RADS (Prostate Imaging Reporting and Data System) is used. This scoring system helps urologists make decisions about whether to biopsy the prostate and, if so, how to optimize the biopsy.


I     most probably benign (clinically significant cancer highly unlikely)

II    probably benign (clinically significant cancer unlikely)

III   indeterminate (clinically significant cancer equivocal) — 20% chance

IV   probably cancer (clinically significant cancer likely) — 50% chance

V   most probably cancer (clinically significant cancer highly likely) —75% chance

Of note, the IV and V groups are the same, differentiated only by the size of the suspicious region. In the IV group the abnormality is < 1.5 cm; in the V group the abnormality is > than 1.5 cm in diameter.

Now let’s play radiologist.  Can you identify the suspicious regions in the following two images?  There is a magnified view of the abnormal sites at the end of this entry.  Radiology clue: when you view images, always be on the look out for asymmetries between the left and right.


Patient 1 with a PIRADS-5 lesion



Patient 2 with a PIRADS-5 lesion with mass effect on the rectum and likely extra-capsular extension

MRI is by no means a perfect test, as clinically significant cancers (particularly small ones) are not always apparent on MRI, and PIRADS-4 and PIRADS-5 lesions when biopsied are not always found to contain clinically significant cancers. An additional concern is its expense.  Some urologists believe in obtaining a prostate MRI on all patients prior to performing a prostate biopsy, whereas others reserve MRI for patients with a previous negative biopsy in the face of a rising PSA. In the former setting, a biopsy remains the only definitive means of assessment regardless of the PIRADS score, one of the key utilities of the MRI being to help precisely target the biopsy.  However, in the latter setting, when the MRI reading is PIRADS-1 or PIRADS-2, a repeat biopsy can often be avoided.

Fact: PSA, DRE and MRI are all useful and informative tests, but the prostate biopsy (tissue sampling) is the only way to know for sure if one has prostate cancer.  In other words, whereas PSA, DRE and MRI are “suggestive,” the biopsy is “definitive.” “The buck stops here” applies to the biopsy.


Magnified view of lesion of figure 1


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Magnified view of lesion of figure 2

Final note: Most insurance companies will readily cover the cost of a MRI study prior to doing a prostate biopsy.  The exception is CIGNA, which apparently cares more about its bottom line than the welfare of its insured patients.  I am constantly fighting with CIGNA-employed physicians in “peer-to-peer” conversations in an effort to get the company to pay for a pre-biopsy MRI.  My last such conversation was two days ago and sadly, I have never prevailed.

Wishing you the best of health,

2014-04-23 20:16:29

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Dr. Andrew Siegel is a physician and urological surgeon who is board-certified in urology as well as in female pelvic medicine and reconstructive surgery.  He is an Assistant Clinical Professor of Surgery at the Rutgers-New Jersey Medical School and is a Castle Connolly Top Doctor New York Metro Area, Inside Jersey Top Doctor and Inside Jersey Top Doctor for Women’s Health. His mission is to “bridge the gap” between the public and the medical community. He is a urologist at New Jersey Urology, the largest urology practice in the United States.

The content of this entry is excerpted from his new book, PROSTATE CANCER 20/20: A Practical Guide to Understanding Management Options for Patients and Their Families

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Video trailer for Prostate Cancer 20/20

Preview of Prostate Cancer 20/20

Andrew Siegel MD Amazon author page

Prostate Cancer 20/20 on Apple iBooks

Dr. Siegel’s other books:

FINDING YOUR OWN FOUNTAIN OF YOUTH: The Essential Guide to Maximizing Health, Wellness, Fitness and Longevity

PROMISCUOUS EATING— Understanding and Ending Our Self-Destructive Relationship with Food

MALE PELVIC FITNESS: Optimizing Sexual and Urinary Health

THE KEGEL FIX: Recharging Female Pelvic, Sexual, and Urinary Health


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One Response to “Prostate MRI: What You Should Know”

  1. Futurology: What Lies Ahead in Prostate Cancer in 2020 and Beyond | Our Greatest Wealth Is Health Says:

    […] recent incorporation of powerful magnets has resulted in more sophisticated multi-parametric prostate MRI capabilities, improving both prostate cancer screening and staging.  PET/CT and PET/MRI imaging […]

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