An imaging doctor says, I often encounter the following questions:

Doctor, I have a heart stent, can I do a magnetic resonance examination?

Doctor, I need to have a magnetic resonance examination, but the heart is let off the stent. The doctor (clinician) asked me to ask if it can be done.

Hello there! MRI? I’m the XX department. One of our patients has undergone interventional surgery. Can I have MR without the titanium clip?

Can a patient with a stent undergo an MRI examination?

What about other implants? Such as heart valve replacement?

We all know that magnetic resonance is a superconducting magnet. The principle of a superconducting magnet is to generate a magnetic field through an energized solenoid, that is, a superconducting ring. The current is constantly rotating in the ring to generate an extremely stable magnetic field. When we are next to a magnetic resonance machine, it is equivalent to being near a giant magnet that is nearly 30,000 times stronger than the earth’s magnetic field. If there are ferromagnetic objects such as coins and necklaces, they will be attracted by this magnetic field. Produces a projectile effect-similar to throwing a object from a height, the object will hit the ground faster and faster.

Carrying metal objects for MRI examination is very dangerous. In 2013, a worker in Liaoning was inhaled into the equipment by a huge magnetic field and iron chains during the installation of magnetic resonance equipment for the hospital, causing him to die. In January 2018, when an Indian man, Rajesh Maruti Maru, accompanied a patient for a magnetic resonance examination, he died of being inhaled into the instrument while carrying an oxygen cylinder.

Some doctors often refuse to do MRI examinations for patients implanted in their body such as cardiovascular stents for risk aversion considerations, but is this really appropriate? For a patient who urgently needs MRI examination (such as acute cerebrovascular disease) or MRI examination has obvious advantages in disease diagnosis and treatment, how can the patient get reasonable treatment under the premise of ensuring safety?

In fact, we already have written evidence and reference materials for this issue. In 2007, the world’s most famous American Cardiovascular Association AHA issued a statement on the safety of cardiovascular devices and magnetic resonance (hereinafter referred to as the statement), which clearly stated the safety of MRI of cardiovascular implants. In October 2017, experts from the Quality Management and Safety Management Group and the Magnetic Resonance Imaging Group of the Radiology Branch of the Chinese Medical Association also formulated domestic MRI safety based on reference to domestic and foreign MRI safety standards and related documents, combined with the actual situation in my country. Management consensus of Chinese experts.

 The safety of different implants in the human body proposed in the consensus on the safety of magnetic resonance examinations.

 1. The amount of ferromagnetic material

The amount of ferromagnetic in the intracranial aneurysm clip will cause danger during MRI examination. There is no conclusion yet. Aneurysm clips made of strong ferromagnetic substances are not allowed to be used for MRI examinations; aneurysm clips made of weak ferromagnetic or non-ferromagnetic substances can be used for MRI examinations below 1.5 T (inclusive).

2. Cardiac implantable electric equipment

Cardiac implantable equipment includes cardiac pacemakers, implantable cardioverter defibrillators, implantable CM (cardiovascular monitors) and implantable cycle recorders, etc., since 1958 Since it was put into application, the number and types have increased, and it has become more and more complex. In 2011, the US marketed the MR-compatible pacemaker (pulse generator) and lead and MR-compatible ILR that were certified by the Food and Drug Administration; in 2015, the MR-compatible ICD was launched. However, many cardiac implantable electronic equipment being used in clinical labs are not compatible with MRI.

Cardiac implantable electronic equipment
Cardiac implantable electronic equipment

3. Other implants for cardiovascular system

 1. Mechanical valve-safety

 According to the 2007 AHA statement, almost all artificial heart valves and annulus on the market are MR safe and can be performed at any time with a magnetic field of ≤3.0T Resonance check.

2. Cardiac suture and occlusion devices-safety

Many suture and occlusion devices are MR safe. The manual will indicate whether the test has been carried out.

In addition, the “wire buckle” that fixes the sternum after surgery has also been proven to be MR safe, but due to the differences in materials in various regions, there may be local thermal effects.

3. Inferior vena cava filter-safety

 Many inferior vena cava filters are MR safe, but there are a few weakly magnetic devices, such as Cooks Gianturco bird nest or Boston Scientific’s Greenfield filter. The guidelines recommend that the best interval is 6 weeks. MR inspection.

 4. Floating catheter-MRI examination is not recommended

Patients with Swan-Ganz catheter should not undergo MRI examination. Although in vivo tests have confirmed that MR images can be obtained safely, there are still possible risks due to catheters, guide wires, etc. A magnetic resonance examination is recommended.

Floating catheter-MRI examination
Floating catheter-MRI examination

5. IABP (Aortic Balloon Counterpulsation)-Absolutely forbidden

 Although no one has conducted a systematic safety evaluation on it, the 2007 statement clearly pointed out that IABP is an absolute contraindication for MR.

6. RI scan of the cochlear implant

MRI scan of the cochlear implant can cause the magnetic pole of the cochlear implant to be reversed, and it should be reset by invasive surgery. Medical experts recommend completely evaluate the risk-benefit ratio of the MRI scan before scanning. During head scans, the probability of magnetic pole piece flipping is less than that of chest, abdomen, and lower extremity scans, it may be related to frequent bed shifts during chest, abdomen, and lower extremity scans, and the larger magnetic field gradient at the edge of the magnetic resonance imaging scan hole. It is recommended for patients who have cochlear implants. Move the bed slowly during MRI. In addition, although the cochlear implant has the risk of heat generation during MRI scans, it is still relatively safe in a magnetic field environment below 1.5 T (inclusive).

7. Orthopedic implants

 Most of these implants are non-ferromagnetic or slightly weakly magnetic. Because they are firmly fixed to human bones, ligaments, or tendons during the operation, they usually do not move. However, an orthopedic implant may introduce image artifacts and it may affect the observation of the surrounding tissues. In addition, there is a chance of thermal burns.

Orthopedic implants
Orthopedic implants

8. Equipment used in surgery and intervention

 It is safe to perform MRI examination after implantation of non-ferromagnetic surgical and interventional equipment and titanium alloy radioactive particle shell. Nowadays, there are different types of puncture needles like biopsy needles, guide wires, catheters, and corresponding monitoring devices that are used for MRI-guided interventional operations.

9. The indwelling catheter and infusion pump and

 Infusion pumps are mostly implanted under the chest and it is consist of a venous catheter system and a puncture seat. The materials are mainly silicone rubber, alloy, and plastic, etc., which are non-ferromagnetic and weakly magnetic, so MRI scan is safe of. Patients should remove insulin pumps because the insulin pump while entering the MRI examination room, because strong magnetic fields may damage the insulin pump function.

10. Dental implants

Dental implants like fixed dentures and porcelain teeth contain alloys and metals, and some are even ferromagnetic. Because the dental implant has been firmly fixed on adhered or the alveolar bone to the corresponding connector and has high strength. It will not move and deform in the MRI equipment with field strength below 3.0 T (inclusive). Dental implants may have some artifacts where they are located.

11. Breast implants and intrauterine devices

 Metal intrauterine equipment is generally made of copper. Nowadays, it has not been found that the intrauterine contraceptive device causes any adverse reactions in MRI examinations below 3.0 T (inclusive), but it may produce artifacts and affect the image quality. Different implants used in breast augmentation and breast plastic surgery are non-ferromagnetic materials. It is safe for these patients to undergo MRI scans, but few plastic accessories may have metal, which should be noted.

12. The Coronary Stent

 “Statement” clearly states that almost all coronary stent products on the market have been tested and have been marked as safe for magnetic resonance (MR). The early peripheral arterial stents (before 2007) may have weak magnetic properties.

All commercially available stent products are quite safe in MRI examinations of ≤3.0T (note that 3.0T is included), and some researchers have confirmed that MR examinations can be performed on the day of stent placement.

Some people worry that the stent will have a thermal effect under a magnetic field to cause the temperature to rise, but experiments have found that this thermal effect is quite limited, generally only a rise of 1-2°C, which is not as high as the body temperature caused by a body fever. Moreover, the blood flow in the internal environment will quickly take away the heat, so there is no need to worry about the thermal effect of the stent magnetic resonance examination.

According to the “Statement”, the following issues can be clarified:

1. At present, both bare metal stents and drug-coated stents are MRI safe; however, the safety of the weak magnetic stent inserted in 2007 needs to be considered.

2. It is usually believed that there is no problem with the magnetic field contact after the stent is implanted for 6 weeks (ie 1.5 months).

13. Peripheral vascular stents

1. The safety of weakly magnetic peripheral arterial stents must be considered.

2. Timing of examination: Unless the MRI examination can give the patient a clear clinical benefit, the MRI examination after peripheral arterial stent placement should be considered after 6 weeks.

It should be noted that although the MRI safety of the stent itself has been confirmed, the metal stent will produce artifacts locally, affecting the observation of the surrounding structure, and it is impossible to evaluate the restenosis in the stent.

Peripheral vascular stents
Peripheral vascular stents

For the radiologist, it should be clear: the type of the patient’s stent, the time of implantation, and the general condition of the patient; as far as possible, the patient is required to carry the stent instructions and perform related operations strictly according to the instructions.

For patients with stent placement, keeping the instructions for the stent is not only a performance that is responsible for personal safety, but also can provide help for future medical examinations. The ultimate benefit is still the patient himself.

On the instructions for inserting the stent, the MRI safety is generally marked as “MR safe”.

14. Artificial heart valve and valvuloplasty ring

All artificial heart valves and valvuloplasty rings available in the market are MRI-safe and can be inspected on an MR scanner under 3.0 T (inclusive) at any time after the surgery. There are differences in products of different manufacturers, the materials should be confirmed before the MRI examination.

15. Intraocular implants

Magnetic intraocular implants can be displaced in a highly strong magnetic field. Such patients should not undergo MRI examination.

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