Penile implants, or penile prostheses, are medical devices surgically placed within the penis to treat severe erectile dysfunction when other treatments have failed. These devices allow a patient to achieve an erection sufficient for sexual intercourse. Patients with implanted medical devices often require diagnostic imaging, and magnetic resonance imaging (MRI) is a common tool for visualizing internal body structures. Concerns arise about the safety of placing a metallic or partially metallic device into the strong magnetic and radiofrequency fields of an MRI scanner. This article addresses the MRI compatibility of penile implants and the necessary precautions patients must take.
MRI Safety Status of Penile Implants
Nearly all modern penile implants are classified as “MR Conditional,” meaning they are safe to use in an MRI environment only under specific, defined operating conditions. This differs from “MR Safe” (no known hazard) and “MR Unsafe” (strictly prohibited). The MR Conditional status requires that the MRI machine’s magnetic field strength, the specific absorption rate (SAR), and the scan duration remain strictly within the limits set by the implant’s manufacturer.
The two main types of prostheses, inflatable and malleable, generally fall under this designation. Inflatable implants are hydraulic systems composed of cylinders, a reservoir, and a pump. Malleable (or semi-rigid) implants are simpler, consisting of paired rods that are manually positioned.
Older models, such as the Dacomed Omniphase and Duraphase from the 1980s and 1990s, contained substantial ferromagnetic metal and are often considered MR Unsafe. Modern implants, like the Coloplast Titan and AMS 700, are designed with non-ferromagnetic materials. They have been verified as safe for MRI scanners operating at 3.0 Tesla or less, covering most clinical systems.
How Implant Materials Affect MRI Compatibility
Modern implants are classified as MR Conditional, not MR Safe, due to minor metallic components necessary for function. The bulk of both inflatable and malleable implants is constructed from non-metallic, biocompatible materials like silicone and polymers, which pose no risk. In inflatable implants, the pump, valves, and connectors often contain small quantities of medical-grade stainless steel, titanium, or MP35N alloy.
For malleable implants, the central core providing rigidity typically contains a silver or stainless steel rod. These trace metal components can interact with the MRI’s static magnetic field, potentially causing a weak deflection force. More importantly, these components can absorb radiofrequency (RF) energy, leading to localized heating, or thermal injury, which is the primary risk associated with MR Conditional devices.
Non-clinical testing shows modern prostheses demonstrate minimal temperature increases, typically less than $2.0^{\circ}C$, when scanned under maximum limits at 3.0 Tesla. This temperature rise is considered safe and falls within accepted standards. Safety requires ensuring the specific parameters used for the scan, including the Specific Absorption Rate (SAR), do not exceed the manufacturer’s tested limits for that implant model.
Essential Pre-MRI Patient Preparation
Prior to any MRI scan, a patient with a penile implant must take specific steps to ensure safety. The patient must notify the prescribing physician and the MRI technician about the implant’s presence. Providing documentation, such as the implant card or a letter from the manufacturer, is highly recommended to confirm the device’s exact model and manufacturer.
Knowing the specific model is necessary because MR Conditional parameters are unique to each device. If the implant is an inflatable prosthesis, it must be completely deflated and secured in the deflated position before entering the MRI suite. Failure to deflate the device can cause pressure changes, potentially resulting in discomfort, structural damage, or unintended inflation during the scan.
Radiology personnel must cross-reference the implant’s information with their safety database. They confirm the specific operating conditions, including the maximum static magnetic field strength and the maximum SAR, that must be programmed into the MRI machine. This detailed communication is the most important factor in guaranteeing a safe MRI procedure.
Potential Risks During an MRI Scan
Even with a modern MR Conditional device, risks exist if manufacturer guidelines are not precisely followed.
Risks Associated with Scanning
The most significant potential adverse event is localized tissue heating, or thermal injury, which can lead to burns around the metallic components. This heating occurs when the radiofrequency energy used by the scanner is absorbed by the metal parts, particularly if the SAR limit is exceeded.
A second risk is the potential for device malfunction or structural damage. The powerful magnetic fields can theoretically stress internal mechanisms or cause unintended inflation if the device is not properly locked down. Although severe complications are rare, device damage could necessitate corrective surgery.
The presence of metal, even in small amounts, can create image artifacts. These artifacts appear as signal voids or streaks on the MRI images and can obscure the area of interest. This limitation is most pronounced if the target area is near the implant site, though technicians can often adjust parameters to minimize the effect.