A penile implant, also known as a penile prosthesis, is a medical device used to treat severe erectile dysfunction when other treatments have failed. These devices are surgically placed within the corpora cavernosa, the two chambers in the penis that fill with blood during an erection. Nearly all modern penile implants are classified as MR Conditional, meaning they can be safely scanned under specific, controlled conditions when an MRI is needed for other medical reasons.
Understanding Implant Materials and MRI Compatibility
The safety classification of a medical device within a powerful magnetic field depends entirely on its composition, placing it into one of three categories: MR Safe, MR Unsafe, or MR Conditional. MR Safe devices pose no hazard at any magnetic field strength, while MR Unsafe devices contain strongly ferromagnetic materials that present an unacceptable risk. The vast majority of penile prostheses fall into the MR Conditional category, meaning they are safe only when scan parameters—such as field strength and radiofrequency power—fall within the manufacturer’s tested limits.
Inflatable Penile Prostheses (IPPs) are the most common type, primarily composed of non-metallic materials like silicone and polyurethane, which are inherently compatible with MRI. However, these hydraulic systems include small metallic components, such as stainless steel springs in the pump valve or titanium extenders. These small amounts of non-ferromagnetic metal necessitate the MR Conditional labeling, requiring specific safety guidelines during the scan.
Malleable or rod implants consist of two rods inserted into the penis that allow manual positioning. These devices are typically made of a silicone sheath covering an internal core, which often includes a silver or stainless steel wire or coil for flexibility and structural integrity. This internal metallic core means that these implants are also classified as MR Conditional. Only older, now-discontinued models, such as the Dacomed OmniPhase and DuraPhase, contained enough ferromagnetic material to be deemed potentially MR Unsafe due to a risk of deflection.
Necessary Safety Protocols Before an MRI Scan
The responsibility for a safe MRI begins with the patient communicating the presence of their implant to the imaging center staff and the referring physician. It is important to inform the radiologist and the MRI technologist about the device. This allows the facility to verify the implant’s specific safety profile against the technical capabilities of the MRI machine being used.
The most precise method for verification is providing the exact model and manufacturer of the device, typically found on a patient implant card or in surgical records. Manufacturers like Coloplast and Boston Scientific provide detailed documentation specifying the limitations for their MR Conditional devices. These limitations often include a maximum static magnetic field strength, commonly 3 Tesla or less, and a specific limit for the radiofrequency power, known as the Specific Absorption Rate (SAR).
The imaging facility must strictly adhere to these verified conditions to ensure patient safety and avoid potential device malfunction. For inflatable devices, some manufacturers may recommend a specific inflation status prior to the scan, though this primarily aids in diagnostic imaging. Following these procedural steps ensures the device remains inert and safe throughout the imaging process.
Physical Effects and Image Distortion During Imaging
During an MRI scan, the powerful magnetic field and radiofrequency pulses can interact with the implant, creating two primary concerns: localized heating and image artifacts. Non-clinical testing of modern MR Conditional implants has demonstrated that any temperature rise is minimal, generally less than 1.9 °C, even under maximum tested conditions. This minor heating, caused by radiofrequency energy interacting with metallic components, is not considered a hazard to the patient.
The risk of the implant moving or vibrating is extremely low for contemporary devices, as they are securely anchored within the body and contain only non-ferromagnetic metals. However, the presence of these metal components inevitably causes a signal void, which is a significant drop in image quality near the device. This phenomenon is known as an imaging artifact, where the metal distorts the magnetic field, creating a dark area that obscures the surrounding anatomy.
The extent of this artifact can be significant, sometimes extending several centimeters from the implant itself. This distortion can compromise the diagnostic value of the scan, particularly if the area of medical interest, such as the prostate or pelvic floor, is directly adjacent to the implant. For this reason, imaging parameters may be adjusted to minimize the artifact, though it cannot be eliminated entirely.