What Should You Not Do Before a Prostate MRI?

Ejaculating in the days before a prostate MRI, arriving with a full bladder, or ignoring bowel preparation instructions can all reduce the quality of the images your radiologist needs to read accurately. Prostate MRI is a powerful diagnostic tool, but it is surprisingly sensitive to controllable factors in the hours and days before the scan. Some of these preparation steps are intuitive, while others are less obvious and rarely explained well to patients ahead of time.

Don’t Ejaculate in the Days Before Your Scan

This is probably the preparation instruction that catches patients most off guard. Ejaculation partially drains the seminal vesicles, which sit just behind the prostate and are important structures the radiologist needs to evaluate clearly. When these vesicles are deflated, they become harder to distinguish from surrounding tissue and from potential areas of disease.

A study comparing men who ejaculated within 24 hours of their scan against men who abstained for at least three days found that total seminal vesicle volume was significantly smaller in the ejaculation group, roughly 6 mL compared to nearly 9 mL in the abstinence group. More critically, readers rated far more scans in the ejaculation group as nondiagnostic for the seminal vesicles.¹ Separate research has also shown that ejaculation lowers the signal intensity of the prostate itself on key imaging sequences, affecting the peripheral zone where most clinically significant cancers arise.²

The standard advice is to abstain from ejaculation for at least three days before the MRI. Some facilities recommend even longer. If your imaging center didn’t mention this, it’s worth calling to ask their specific policy, because a suboptimal seminal vesicle assessment could mean the difference between a definitive read and being called back for a repeat scan.

Don’t Ignore Bowel Preparation

Gas and stool in the rectum sit directly against the back wall of the prostate, and they are among the most common causes of degraded image quality. Rectal gas is especially problematic because it creates distortion on a key imaging sequence called diffusion-weighted imaging (DWI), which is central to detecting cancer. A study measuring the relationship directly found a strong correlation between how distended the rectum was and how much distortion appeared on DWI.³

Many centers now ask patients to use a small enema (often called a micro-enema or Fleet enema) an hour or two before the scan. The evidence supporting this is reasonably consistent. One study found that micro-enema use significantly reduced rectal gas and improved DWI quality for both radiologists reviewing the scans.⁴ Another study comparing different bowel preparation strategies found that micro-enema was the only technique that significantly improved DWI and overall image quality, whereas dietary restrictions alone or anti-spasmodic drugs alone did not help.⁵

That said, not every study shows a dramatic benefit. A Fleet enema study found that while the enema did reduce rectal diameter, the improvement in subjective image quality was inconsistent between readers, with one radiologist seeing significant benefit and the other not.⁶ The bottom line is that bowel prep likely helps and is unlikely to hurt, but the size of the benefit varies. If your center provides an enema and instructions, follow them. If they don’t, you can ask whether they recommend one.

Some centers take a more aggressive approach and place a thin rectal tube during the scan to evacuate gas in real time. Research has shown this approach significantly reduces rectal gas, decreases DWI distortion, and improves image quality.⁷ This isn’t a decision you make yourself, but it’s worth knowing that it exists if you’re comparing imaging centers or wondering why one facility’s protocol includes it and another’s doesn’t.

Don’t Arrive with a Full Bladder

You might assume that a full bladder helps by pushing structures into better positions, similar to how it’s used during pelvic ultrasound. For prostate MRI, the opposite is true. A very full bladder pushes the prostate downward and can physically shift its position by several millimeters between sequences. In men whose bladder volume more than doubled during the scan, the prostate shifted an average of about 3.5 mm, compared to less than 2 mm in men with more stable bladder filling.⁸ That kind of movement between sequences means the images may not line up properly, making it harder for the radiologist to correlate different types of images at the same spot.

Interestingly, a recent study found that bladder volume alone wasn’t significantly associated with motion artifacts on T2-weighted images, though rectal volume was.⁹ So the problem with a full bladder isn’t so much blurring within a single image sequence, but rather that the prostate drifts as the bladder fills during the 30-to-45-minute scan. The practical advice: empty your bladder shortly before the exam, then drink only small sips of water if you’re thirsty. You want a comfortably empty bladder, not a painfully full one.

Don’t Schedule Your MRI Too Soon After a Biopsy

If you’ve recently had a prostate biopsy, scheduling the MRI too quickly afterward is one of the most impactful mistakes. Biopsies cause bleeding inside the prostate that shows up as dark signal on MRI, which can obscure actual lesions or mimic disease that isn’t there. A study examining the timing between biopsy and MRI found that men scanned earlier (averaging about 25 days after biopsy) had significantly more hemorrhage-related artifacts and more discordance between MRI findings and surgical pathology compared to men scanned later (averaging about 38 days). The researchers concluded that waiting at least four weeks after biopsy is necessary for reliable imaging.¹⁰

Many guidelines now recommend waiting six to eight weeks if possible, and some centers prefer even longer for men who had extensive biopsies with many cores taken. If you’re being asked to schedule a prostate MRI and you’ve had a recent biopsy, bring this up with your urologist. The trend in recent years has actually been to perform the MRI before biopsy rather than after, which sidesteps this problem entirely. If your clinical situation allows it, getting the MRI first and then doing a targeted biopsy based on the MRI findings is generally the better sequence.

Don’t Forget to Mention Hip Replacements or Metal Implants Near the Pelvis

Metal hip implants are a common issue for men in the age range most likely to need prostate MRI. The metal creates susceptibility artifacts, which are distortions in the magnetic field that warp images, especially on diffusion-weighted sequences that are critical for cancer detection.¹¹ The severity depends on the type of metal, the number of implants, and the MRI scanner’s field strength.

This doesn’t mean men with hip replacements can’t get a useful prostate MRI, but the imaging team needs to know about the implants ahead of time so they can adjust their scanning technique. Research using specialized artifact-reduction methods has demonstrated that high-quality images can be obtained even with bilateral hip replacements, but the standard scanning protocol won’t work.¹² If you don’t disclose the implants when scheduling, the technologist may not set up the scanner appropriately, and you could end up with unreadable images and a wasted appointment. The same goes for any other metal hardware in the pelvis or lower spine.

Don’t Take Certain Dietary Supplements Without Mentioning Them

This one is genuinely obscure, but worth knowing. A case report documented a patient whose pelvic MRI was ruined by susceptibility artifacts traced back to curcumin supplements. After the patient stopped taking curcumin, a repeat MRI one week later was completely artifact-free. The likely explanation is that curcumin’s iron-chelating properties led to iron accumulation in the bowel, and that concentrated iron created magnetic field distortions during the scan.¹³

Iron supplements themselves could plausibly cause similar problems if undigested iron is sitting in the rectum during the scan. This hasn’t been extensively studied, but the physics is straightforward: concentrated ferromagnetic material next to the prostate will distort the images. If you take iron tablets, high-dose curcumin, or other supplements that could deposit iron or magnetic minerals in your gut, mention this to the imaging center when you schedule the scan. They may ask you to pause them for a day or two before the exam.

Active Infections and Inflammation

Going in for your MRI while you have an active prostate infection (prostatitis) or significant pelvic inflammation is another less-discussed problem. Inflamed tissue can light up on MRI in ways that closely mimic cancer, leading to false-positive findings that generate unnecessary worry and additional biopsies. A study examining false-positive MRI-targeted biopsies found that over half of the lesions flagged on MRI in men who turned out to have no cancer in those areas had inflammation on pathology.¹⁴

If you’re currently being treated for a urinary tract infection, prostatitis, or you’ve recently had any urethral instrumentation (catheterization, cystoscopy), tell your urologist before proceeding with the MRI. Depending on the situation, it may be better to complete a course of antibiotics and let things settle down before scanning. The inflammation itself won’t necessarily make the scan technically impossible, but it can make interpretation much harder and less reliable.

What About Anti-Spasmodic Injections?

Some imaging centers administer an anti-spasmodic drug (commonly hyoscine butylbromide, marketed as Buscopan in many countries) before or during the scan to reduce bowel movement that can blur images. A UK-wide survey of prostate MRI practice found that about 69% of centers were using anti-spasmodic medication as part of their protocol.¹⁵ The evidence for its benefit, however, is genuinely mixed. One study found it significantly improved the quality of certain image sequences.¹⁶ Another concluded there was no significant advantage when scanning at higher field strength, suggesting it may not be mandatory.¹⁷

This isn’t really something you control as a patient. If the center’s protocol includes an anti-spasmodic, they’ll administer it. But if you have contraindications to these drugs (such as certain heart conditions, glaucoma, or a history of severe reactions), make sure to flag that before your appointment. The scan can still proceed without it. Note that hyoscine butylbromide is not available in the United States, where glucagon is sometimes used instead, though its use in prostate MRI is less standardized.

Practical Pre-Scan Preparation Checklist

Imaging centers vary in how much preparation guidance they give patients, and that variability is surprisingly wide. That same UK survey found that only about 14% of centers even gave bowel preparation instructions to patients.¹⁵ So if you’ve received minimal guidance, it doesn’t mean preparation doesn’t matter. Here’s what the evidence supports:

Abstain from ejaculation: At least three days before the scan. Longer is fine.
Empty your bowel: If given a micro-enema, use it as directed. If not, try to have a bowel movement before leaving for the appointment.
Empty your bladder: Urinate shortly before the scan begins. Don’t drink large volumes of fluid in the waiting room.
Disclose implants: Mention hip replacements, spinal hardware, or any other metal near the pelvis when scheduling.
Mention supplements: Particularly iron and curcumin, which can affect image quality through artifacts in the bowel.
Flag infections: If you have symptoms of prostatitis or a UTI, discuss timing with your urologist.
Ask about biopsy timing: If you’ve had a prostate biopsy within the last six weeks, confirm with your doctor that enough time has passed.

Endorectal Coils and Why They’re Becoming Less Common

Older prostate MRI protocols often used an endorectal coil, an inflatable receiver placed inside the rectum to boost signal from the prostate. These coils improved signal quality but came with trade-offs: they were uncomfortable, they created their own set of artifacts (including aliasing, ghosting, and signal intensity drop-off), and they could actually deform the prostate’s shape. Studies have found that while endorectal coils did reduce motion artifacts compared to external coils, they produced more of these other artifact types.¹⁸ Comparisons showed that susceptibility artifacts were more frequent with endorectal coils than with external pelvic coils.¹⁹

Newer external pelvic coils at 3 Tesla field strength have largely closed the signal quality gap. One study comparing an external wearable pelvic coil to an endorectal coil found that while the endorectal coil still had higher raw signal, artifact severity on key sequences was also significantly worse with the endorectal approach.²⁰ For patients, this is mostly good news: most modern imaging centers no longer use endorectal coils for routine prostate MRI, which eliminates one uncomfortable element of the exam. If a center still uses one, it’s not necessarily a problem, but it’s worth asking whether it’s truly needed on their particular scanner or whether an external coil protocol is available.

Understanding the shift away from endorectal coils also explains why some older preparation instructions you might find online (such as fasting specifically to reduce coil-related artifacts) may no longer apply. Preparation guidance evolves alongside imaging technology, so always follow the specific instructions from the facility performing your scan rather than generic advice from an outdated source.