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Magnetic resonance imaging radically changed the approach to diagnostics, increased the level of efficiency and quality of medical care. If before, doctors could detect many diseases only during surgery (and in the worst case, at autopsy), now they have the opportunity to literally look inside the patient. And to see such minor pathologies as a pituitary tumor, which itself weighs no more than 1 gram! But it turned out that some people cannot even enter the radiation therapy office. What is it connected with?
Why is "magnetic diagnosis" not suitable for all patients?
The method of visualization using a magnetic field is practically ideal: it does not use X-ray radiation, perfectly shows the muscles, bones of the skull, brain, spine and joints, scans tissues at any depth even under the skull, is suitable for examining pregnant women and infants. But it has one feature related to the magnetic properties of materials.
As is known, many metals react to an external magnetic field. And modern medicine actively implants various devices, pins and plates for fracture fusion, joint replacement, and heart rhythm stimulation. Can patients after this do an MRI of the brain or spine?
Is it possible to do MRI with metal implants?
All substances that react to a magnetic field are divided into 3 types:
- paramagnets (titanium, aluminum, etc.) - do not have magnetic properties and practically do not react to an external magnetic field;
- diamagnets (silver, gold) - weaken the magnetic field and are pushed out of it;
- ferromagnets (iron, alloys with nickel and cobalt) are heated and magnetized in a magnetic field.
Therefore, it is quite possible to do an MRI in Moscow with titanium plates, needles and pins. With iron or steel elements (for example, with bullets and shrapnel from shells) - it is impossible.
What should patients with endoprostheses do
In surgery according to ISO 5832 and GOST R ISO 14708, implants made of various alloys are used:
- cobalt, molybdenum, chromium;
- cobalt, chromium, iron, nickel, tungsten, molybdenum;
- titanium, aluminum, niobium, etc.
Also, endoprostheses for joints are now made of various polymers and ceramics.
What endoprostheses are MR-compatible? Only those that do not exhibit magnetic properties.
The question of whether a patient with an endoprosthesis can be diagnosed should be decided by a doctor. In this case, everything depends on the materials from which the artificial joint is made.
Active implanted devices
Medicine has long been able to replace a patient not only with a destroyed joint, but also to implant a cardiac rhythm driver, install an electrostimulator of the auditory pathways or a neurostimulator of the central nervous system. Any active stimulator is a miniature computer that works from a power source, that is, batteries. And devices, as is known, react to a strong magnetic field. Therefore, previously patients with pacemakers could not even cross the threshold of the radiation therapy room.
But manufacturers of active implants keep up with the times. Therefore, many of them now make MR-safe cochlear devices and cardiac pacemakers, with which you can undergo diagnostics.
But still, they have limitations. Some manufacturers indicate that with implanted devices it is possible to do MRI on devices with induction of a magnetic field up to 1,5 T. But choosing such a device is not a problem. For example, on the site MRT-Diagnostic.ru you can find out all the necessary information about the induction of the device, its design.
An important feature is the type of device. There are closed and open tomographs. The first ones are usually more powerful and give a more detailed image, but they are not suitable for patients with claustrophobia due to the tunnel. The latter are often inferior to closed ones in terms of power, but are suitable for people suffering from a fear of confined spaces and very obese patients.
