Definition
In recent years, MRI has become increasingly important in non-invasive diagnostics. With the help of a strong magnetic field and electromagnetic waves, various tissues in the body can be visualized. However, these can also act on implants in the body.
Implants are artificial materials that are permanently or long-term inserted into the body (e.g. prostheses, cochlear implants, artificial heart valves, etc.). Some metal-containing implants pose risks for the patient and can influence the image quality. Therefore, in recent years, more and more implants have been produced that allow MRI imaging without any risks for the patient.
How does an implant affect image quality?
The effects on the image quality of the MRI depend on the materials and size of the implants. Especially with ferrous (ferromagnetic) materials, considerable artifacts can be seen. Locally missing image information (‘erasures’), distortions in the image and spatial mis-coding (structure is imaged in the wrong place) are possible.
In contrast, artifacts occur less frequently with titanium-containing implants. The cause of the disturbance of the image quality is a local disturbance of the magnetic field in the body. In the vicinity of the magnetic materials, the magnetic field is disturbed in a way that cannot be registered by the detectors of the MRI.
Frequently, bright lines are found at the edges of the disturbances, which can be misinterpreted by the doctor. To minimize the effects of implants on image quality, special imaging techniques have been developed in recent years to improve imaging. Special metal sequences can be used to minimize artifacts and distortions. To this end, it is important that the patient informs the physician about implants or other possible metallic structures in the body so that this special MRI scan can be performed. Usually, MRI devices with a magnetic field strength of 1.5 Tesla are preferred.
Risks of an MRI with horizontal implants
Risks for the patient with implants can arise both from the strong magnetic field and from the radio waves emitted (high frequency). The radio waves emitted by the MRI machine lead to the induction and conduction of an electric current in metals. This leads to a strong heating, which can cause 1st degree (superficial) to 3rd degree (deep) burns.
With the implants used today, however, this is extremely rare due to the avoidance of harmful materials. In addition, the strong magnetic field can attract and move magnetic metals (including iron). This attraction or movement depends on the position and stability of the materials: the assessment of possible risks is the sole responsibility of the physician.
With the exception of a few implants, which are guaranteed by the manufacturer to be MRI-compatible, the physician must weigh up the risks and benefits of imaging. In some cases, other imaging techniques may be used.
- Large screws, such as those used in the spine, arms and legs, do not normally pose a risk.
- Small and loose materials (e.g. fresh stents) can be moved by the magnetic field and thus damage surrounding structures.
