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What you should know about MRIs

Updated: 2022-07-20


I. What is an MRI?

MRI, short for magnetic resonance imaging, is a common clinical imaging method. When the human body is placed in a magnetic field during an examination, an MRI uses the difference in hydrogen proton content in the human body for imaging.

With no trauma or radiation, high soft tissue resolution, and clear images, MRIs can help doctors "see" early lesions that are not easy to detect, and they are widely adopted in the diagnosis of various clinical lesions in body parts such as the brain, heart, large blood vessels, chest and abdomen, and joints.

II. Can pregnant women, infants and young children receive MRI examinations?

An MRI does not emit radiation and generally will not affect the fetus.

The first trimester is the key stage for fetal nervous system development, so an MRI is not recommended. Fetal MRIs can be performed in the second and third trimesters, as they can clearly show the development of the fetal brain, chest, abdomen, limbs and major systems, so as to screen for various diseases in the fetal nervous system, respiratory system, and digestive system. Fetal MRIs have been widely used in clinical practice.

Infants and young children can receive MRI examinations, but it is recommended that the examination be performed when the baby is asleep or after using sedatives, due to the long examination time and potentially disturbing noise.

III. Can MRI examinations be performed if one has implants such as cardiac pacemakers, steel nail stents, or false teeth?

It is not impossible to perform MRI examinations if a patient has implants with certain material properties. Common implants are as follows:

1. Cardiac pacemakers: MRIs cannot be performed in most cases.

In a strong magnetic field, the cardiac pacemaker may experience phenomena such as device displacement, abnormal pacing signal, abnormal activation of defibrillation mode, and electrode heating, which will cause adverse consequences. Most cardiac implantable electronic devices currently in clinical use are not recommended for MRIs.

2. Orthopedic implants: Whether MRIs can be performed or not depends on the material properties.

Orthopedic implants such as steel plates, steel pins, screws and various artificial joints have been firmly fixed to the bones, ligaments or tendons during operation and usually will not move, but the risk cannot be ruled out. Proper assessments should be performed prior to the examination. Those with orthopedic implants made of pure titanium or titanium alloy can receive an MRI examination, but such implants may cause image artifacts and thus affect the observation of surrounding tissues.

3. Infusion ports and indwelling catheters: MRIs can be performed.

The infusion port is usually implanted under the skin of the chest and consists of a puncture seat and an intravenous catheter system. The materials are mainly alloys, silicone rubber and plastics, which are non-ferromagnetic and weakly magnetic. Therefore, it is safe to perform MRI examinations, but image artifacts may be caused by the implants. Indwelling catheters are generally made of non-metallic materials and MRI examinations can be performed.

4. Prosthetic heart valves and annuloplasty rings: MRIs can be performed after evaluation.

Most prosthetic heart valves and annuloplasty rings currently on the market are MRI-safe, but due to differences in products from different manufacturers, the materials should be confirmed before an MRI examination.

5. Intrauterine devices (IUDs) and breast implants: MRIs can be performed after evaluation.

The metal IUDs currently in clinical use have not been found to cause obvious adverse reactions in MRI examinations at 3.0 T and below, but may produce large artifacts. It is recommended that the IUDs be removed before the examination if possible.

Most implants used in breast plastic surgeries and breast augmentations are non-ferromagnetic materials, so MRI examinations are safe. However, some plastic materials may contain metal, and MRI examinations should be performed after evaluation.

6. Dental implants: Whether an MRI can be performed or not depends on the material properties.

Dental implants such as implanted teeth, fixed dentures and porcelain teeth mostly contain metal materials. Removable dentures should be removed if possible before the examination, and an evaluation of the materials should be carried out if the dentures are non-removable.

IV. Preparations before MRI examinations

1. Metal objects will not only affect the MRI imaging quality, but may also lead to safety risks in the magnetic field, so the patient must remove all metal objects on the body before the examination, including underwear, belts, lighters, coins, mobile phones, watches, keys, necklaces, clips, earrings, etc.

2. Patients receiving upper abdominal and full abdominal examinations should fast for eight hours and perform breathing exercises before the examination.

3. Patients receiving pelvic examinations need to keep their bladder moderately full, and females should remove IUDs before the examination.

4. Children who require sedation should be prepared in terms of diet and sleep in advance according to the doctor's instructions.