Magnetic resonance imaging (MRI) is a non-invasive imaging test that can be used to help treat and/or diagnose men with prostate problems.
It uses a powerful magnetic field, radio waves, and a computer to produce d spatial resolution images of the prostate.
Since an MRI does not emit x-ray radiation, it is safe to undergo multiple times. There are no side effects associated with the procedure.
A typical scan can take up to 45 minutes and is performed by a radiographer. During the MRI exams, the patient is asked not to move while the machine is actively scanning.
The MRI has long been used as a tool to help find and identify cancerous growths. For prostate cancer, it has been used in the past to help define the disease stage before implementing aggressive treatments such as radical prostatectomy or radiation therapy.
When used, it can provide detailed information on the spread of disease beyond the prostatic capsule. It can also help to determine the involvement of the neurovascular bundles and seminal vesicles.
However, until recently, this usage was limited to men with existing prostate cancer. And it was not used as a diagnostic tool in that application.
Recent improvements in MRI techniques have enabled doctors to expand their use more to the diagnostic realm.
In addition, this new role allows it to be used as an additional diagnostic tool to help determine the need for a biopsy. It has the valuable ability to identify with reasonable accuracy aggressive verses non-aggressive or indolent tumors.
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Conventional Screening for Prostate Cancer
The methods of screening for prostate cancer pca commonly used by urologists today are the prostate-specific antigen (PSA) blood test and the digital rectal examination (DRE).
Neither is a conclusive test for prostate cancer. Currently, there are no blood or urine-based markers that can reliably detect prostate cancer.
Prostate Biopsy
The usual diagnostic procedure is that if either of the above tests is suspicious, a prostate biopsy is usually ordered. Most prostate cancer diagnosed today is the result of a prostate biopsy. 1
A biopsy is an aggressive procedure where several tissue samples are taken from the prostate to be evaluated in the laboratory. The procedure requires a probe containing the biopsy needles to be inserted into the rectum. Guided by ultrasound, the practitioner positions the biopsy needles towards the most suspicious areas.
This screening, known as a transrectal ultrasound-guided (TRUS) biopsy, has resulted in a significant increase in the detection of prostate cancer.
While many new prostate cancers have been diagnosed with this approach, it is not a foolproof diagnostic tool. It may fail to detect lesions, primarily when located in the anterior parts of the gland.
Also, a TRUS can not reliably differentiate between high-grade aggressive prostate cancer and lower grade, less risky tumors. It is well-known that this approach results in significant overdiagnosis and overtreatment.
A prostate biopsy is an invasive procedure that carries several risks. Since most biopsies enter the prostate through the rectal channel, it is highly possible some fecal matter, and its attendant E. Coli bacteria can be introduced into the prostate during the procedure, initiating an infection.
Other risks include:
- bleeding at the biopsy site
- rectal bleeding
- blood in the semen or urine
- orgasm or erectile problems
- difficulty urinating.
These side effects often self-resolve over a month or two. However, a biopsy induced prostate infection can result in hospitalization and be life-threatening.
Cancer found using the conventional approach is often difficult to classify. While the biopsy may find a cancerous tumor, there is no reliable way to determine its aggressiveness.
Unfortunately, some urologists use any positive biopsy cancer finding by as a reason to perform aggressive treatment, typically a radical prostatectomy.
Some of these aggressive procedures can be eliminated if there were a better way to determine if prostate cancer is of a type that is unlikely to spread. Many times, a biopsy finding of cancer results in prostatectomy almost automatically. This is with little regard to the possibility that the tumor might be indolent.
When removed prostates are examined in the laboratory, the finding is often that the disease was not clinically significant. Such over-treatment dooms a patient to live with the significant side effects of an unjustified prostatectomy for life.
What is Multiparametric Magnetic Resonance Imaging?
Multiparametric Magnetic Resonance Imaging (mp-MRI) of the prostate has been used for several years as a tool to help define the disease stage for men with known prostate cancer. It is an advanced form of MRI technology that allows specially trained radiologists to detect and evaluate prostate tumors.
It is usually used prior to implementing aggressive treatments such as radical prostatectomy or radiation therapy. In this setting, its role is essentially to supplement standard anatomical T1 and T2- weighted imaging. It does so by providing additional information on other parameters, hence the term “multiparametric.”
Recently, the mp-MRI has gained acceptance as a useful tool for guiding diagnostic prostate biopsies. In this setting, it is used to grade a level of suspicion for multiple areas of the prostate.
It also guides the biopsy sampling towards the most likely regions of clinically significant disease. Thus, by selectively targeting suspicious areas, it can improve the detection of high-grade cancer while avoiding the detection of low-grade (or indolent) disease. 2
In addition, recent studies have shown that the mp-MRI, when analyzed by a specially trained radiologist, can be used to determine whether or not an invasive biopsy is genuinely warranted.
Autopsy studies of men that died from causes unrelated to their prostates have found that a high percentage of men harbor prostate cancer that does not become aggressive or cause them other problems. This disease, called indolent prostate cancer, is often detected on TRUS biopsies and often results in further aggressive treatment.
It is difficult, if not impossible, to differentiate between types of prostate cancer. Many parameters are used to attempt to assign a value to a tumor and determine whether or not it is likely to spread outside of the prostate.
Thus, while indolent prostate cancer tumors may not progress for many years and never result in further problems, it often leads to unnecessarily aggressive treatment, including prostatectomy.
Men who have had aggressive prostate surgery are invariably left with many side effects. It is critical to be able to determine not only the extent of the disease but also its likelihood of causing future problems.
How an MRI can Help With Diagnosis
An MRI may be ordered prior to a biopsy or after one if cancer is detected to define the extent of disease further.
Anterior tumors tend to be missed by TRUS biopsy until they grow to a substantial size or reach within 15–20 mm from the posterior margin of the prostate. Also, TRUS biopsy has historically been shown (following lab analysis of removed prostates) to underestimate the final Gleason score grade of tumors. 3
For example, men with elevated PSA levels and a negative biopsy are sometimes assigned to an “active surveillance” program. This is for long-term monitoring.
However, studies show that the conventional approach can inadvertently assign approximately 25 percent of patients to active surveillance that actually has more aggressive cancers and need treatment.
There is no real agreement on an optimal way to assign men to active surveillance. The conventional approach of prostate screening (PSA, DRE, TRUS biopsy) for men being considered for active surveillance is known to misclassify patients.
One of the new roles this advanced mp-MRI imaging has gained is that of in guiding targeted diagnostic prostate biopsies. By using its enhanced imaging qualities, it can help ensure more accurate risk stratification. This allows a more positive way of determining long-term risk.
Thus, MRI of the prostate has become an essential component of optimizing patient selection for active surveillance. It provides high predictive confidence for clinically significant disease. Therefore, it can provide reassurance to patients that their disease is truly low risk.
A more exciting new role for the mp-MRI is to eliminate the biopsy completely. A properly trained radiologist can evaluate tumor aggressiveness from the images by carefully examining the tumor’s cell structure.
Studies show that MRI can detect clinically significant disease in one-third to one-half of men. Thus, it can be used to stratify patients. Especially those with the low-risk disease at the start of active surveillance. 4, 5 Judicious use of the MRI can allow more precise treatment stratification options.
How This New Technology Works
The imaging enhancements of the new technology have allowed it to be used in a new role. Today, it can be dedicated to improving biopsy accuracy by better identifying suspicious areas of the prostate.
Prostate cancer is being diagnosed today almost precisely the same way it was diagnosed more than 20 years ago. Unfortunately, a prostate biopsy, where tissue samples are taken, remains the only way prostate cancer is definitively diagnosed.
Negative biopsies are those that do not find cancer. This, of course, is a huge relief for the patient, but the current method of biopsy sampling is essentially random. Thus, a biopsy may be negative simply because the sample needles missed a tumor.
New research has shown that an mp-MRI can provide important diagnostic information in a non-invasive way. This can reduce biopsy-related complications like infection. It can also improve the detection of clinically significant cancers.
The process begins with MRI imaging of the prostate. A specially trained radiologist reviews the images. Any area where prostate tissue deviates from the appearance of normal tissue is deemed suspicious and graded accordingly.
The MRI scan images are viewed by the radiologist in 3-dimensions with detailed tissue contrast. This allows a precise comparison of suspicious areas to normal prostate tissue. These high resolution, detailed images, called T2 weighted images, provide the clearest images of prostate tissue.
It is known that the density of cells varies in cancerous prostate tissue. Using a technique called diffusion-weighted imaging, the radiologist can examine areas where the cells are packed more densely. These densely packed cells tend to restrict free water motion in the tissue causing the area to appear darker on the images.
In addition, blood flow through these areas is disturbed by normal prostate tissue. The observed parameters are weighted according to the severity and mapped. Areas of the highest weight are the most suspicious of the presence of a cancerous tumor.
The noted suspicious areas are then mapped into a three-dimensional model of the prostate to allow biopsy sampling of the suspicious regions. The accuracy of this new technology far exceeds the old method of random sampling. It also does less damage to the organ itself and reduces other biopsy risks.
The ultimate aim of this new technology is to identify areas of concern. And if a biopsy is in progress or scheduled, to aim specifically for the suspicious areas. This allows the biopsy to be more focused and helps eliminate the destruction of healthy tissue in the process. 6 7
Associated Costs and Considerations
An MRI is of the prostate is considered a type of prostate cancer screening. However, it is not covered by all insurance plans. Medicare covers the costs of a:
- doctor ordered diagnostic prostate MRI
- digital rectal exams
- prostate-specific antigen (PSA) blood tests once every 12 months for men over 50.
However, Medicare generally only covers 80 percent of these costs. The remaining costs may be fully or partially covered by supplemental insurance. But, any remaining uninsured costs are the responsibility of the patient. Not all labs and facilities that provide scans to accept Medicare assignment.
A diagnostic MRI in the US can cost up to $3000 depending on the geographical area and the facility. This, of course, is significantly less than a PSA test combined with a biopsy. But, the cost should not be the determining consideration.
However, the higher cost of an MRI is a major issue that can put it out of reach of uninsured or under-insured patients. This may improve as the technology becomes more available, more radiologists are trained to interpret and analyze images, and more physicians become proficient in the associated techniques.
Unfortunately, all diagnostic methods for prostate cancer carry some risk of missing significant clinical disease that is truly present. Hopefully, as technology use becomes more widespread, the cost will be reduced. And, as time progresses, the technology will also see improvements in accuracy as well.
Practical Discussions
Almost every article about prostate cancer begins with statistics on how many cases are diagnosed yearly.
A man recently diagnosed with prostate cancer may read such statistics with trepidation and fear. He might also be overwhelmed by the sheer volume of information available. Doctors often push treatments they are familiar with. And many men will accept the recommendation of a urologist without question or further research.
When the diagnosis is on an older patient, particularly if one with significant other co-morbidities, all options should be explored. The goal is to avoid radical treatment where it would not prolong life.
When it comes to prostate cancer treatment, there seem to be two distinct classes of men. Those that feel they must get immediate treatment (usually surgery), and insist on it. Those that will turn to research and other opinions to pursue their options.
Men that insist on getting immediate treatment will typically depend solely on their urologist for advice and treatment recommendations. Prostate cancer is typically slow-growing cancer. Treating it in a hurry often benefits the practitioner but rarely the patient.
The aware man will read and consult with knowledgeable practitioners. They will also get other opinions and investigate different treatment methods.
All medical treatments for prostate cancer carry significant side effects, many of them sexual. Some of these side effects might be delayed for several years (especially for radiation), but many are immediate. Virtually all of them are permanent.
Conclusion
Information obtained by mp-MRI represents a significant addition to the conventional methods of diagnosis and treatment of prostate cancer.
When used in conjunction with an ultrasound-guided biopsy, it can detect clinically significant disease with reasonable accuracy.
It can also identify the lower level and clinically indolent disease, thus providing more precise treatment options.
Enhanced prostate MRI imaging analyzed by specially trained radiologists has the potential to reduce unnecessary biopsies. It can also reduce risks, thus reducing potential patient side effects, discomfort, and costs. MRI mapping of suspicious prostate areas also allows for better correlation of samples if multiple biopsies are needed.
With the standardization of imaging findings, suspicious areas identified by MRI correlate well with the likelihood of clinically significant disease. This allows for prebiopsy risk stratification. It can also permit reasonable determination of the individual need for a biopsy.
MRI can be of benefit to men with relatively small localized prostate cancer prior to selecting a definitive therapy or entering into active surveillance.
For example, men with a rising PSA that have had one or more negative standard prostate biopsies can now get a more definitive diagnosis. This may eliminate the need for subsequent biopsies.
Thus, a man currently in an active surveillance program may take comfort in knowing that more evidence will be forthcoming in the near future. Moreover, as long as his disease remains stable, he can proceed with reasonable confidence.
MRI testing at regular intervals can also help identify a shift towards more aggressive disease. This can help to eliminate the adverse effects and damage associated with multiple biopsies.
For men that have already been diagnosed with prostate cancer, an MRI can help to optimize tumor parameters allowing better staging and risk stratification. This can help select appropriate candidates with the low-risk disease for active surveillance, as well as monitor them for disease progression.
The MRI has proven to be useful through its sensitivity and specificity in differentiating between clinically significant disease in a setting where a patient has an elevated PSA level with no prior biopsy or a prior negative biopsy.
Advances in MRI imaging has brought changes to techniques that have been the standard for many years. These changes have been greeted with enthusiasm by both practitioners and patients alike, especially among patients currently in an active surveillance program.
Continual future improvements in prostate mp-MRI scanning will likely provide more benefits for detecting prostate cancer.
In the near future, mp-MRI will likely become the preferred imaging modality for risk assessment of prostate cancer. Growing evidence supports its ability to isolate clinically significant from indolent disease. This makes it a valuable tool for reducing over-detection and over-treatment.
