Today a friend asked me if his wife was 3 months pregnant, took her mother to the hospital for a physical examination, and after passing through the MRI door, whether she would be exposed to radiation and whether there would be any bad effects on the fetus. MrI, when they hear the word "nuclear", many people naturally think of radiation, and many hospital MRI examination rooms have yellow warning signs on the doors, which seems to be prohibitive. In fact, MRI has no ionizing radiation, and now the hospital has habitually changed its name to "magnetic resonance".
The magnetic resonance machine is equivalent to a huge magnet, using this applied magnetic field, acting on the hydrogen nuclei in the water molecules in the human body, forming a high-wave number of waves of resonance images, which have been calculated by the computer and made images. In short, tissues with many water molecules, MRI is effective, such as muscles, brain, hepatobiliary pancreas, spinal cord, bone and other lesions are very clear. Tissues with few water molecules are less effective, such as the lungs, most of which are composed of air-containing alveoli, and the air in these alveoli does not contain water molecules, so the magnetic resonance test is ineffective. There are also cavity organs such as the stomach, esophagus and intestines, which contain more gas and have poor magnetic resonance effects.
Therefore, magnetic resonance imaging and CT examination, each with its own advantages and disadvantages, are very important examination methods in the clinic and can complement each other. To say that the harm of magnetic resonance, in fact, there is no big harm. Mr. MAGNETIC resonance imaging is time-consuming, noisy, and in tight spaces, people with claustrophobia may be more fearful. In addition, since the magnetic resonance machine is a huge magnet, it cannot have metal inside and outside the body.
Regarding the safety of magnetic resonance imaging, a Chinese expert consensus was released in 2017, which pointed out the following situations:
1. Intracranial aneurysm clip: Aneurysm clips of strong ferromagnetic materials are prohibited for MRI examination; aneurysm clips of non-ferromagnetic or weak ferromagnetic materials can be used for MRI examinations below 1.5 T (inclusive).
2. Cardiac implantable electronic devices: including pacemakers, ICDs, implantable cardiovascular monitors (CM) and implantable circulation recorders (EHRs), etc., can not be tested for MRI examination.
3. Cochlear implant: Cochlear implant is an electronic device. MRI scans may cause cochlear poles to be flipped and require reduction by invasive surgical methods, and it is recommended to fully assess the risk-benefit ratio of MRI before scanning.
4. Orthopedic implants: Orthopedic implants (such as steel plates, steel needles, screws and various artificial joints, etc.) are mostly non-ferromagnetic or a small amount of weak magnetism, because they have been firmly fixed on the bones, ligaments or tendons during surgery, and usually do not move. But implants may introduce image artifacts that affect the observation of surrounding tissue. There is also a risk of thermal burns. Therefore, MRI is generally not recommended.
5. Surgical and interventional equipment: At present, there are all kinds of puncture needles, biopsy needles, catheters, guide wires and corresponding monitoring equipment specially used for MRI-guided interventional surgery. In addition, the implantation of radioactive particles under MRI guidance also requires corresponding non-ferromagnetic equipment, and the shell of the radioactive particles is titanium alloy material, and it is safe to perform MRI examination after implantation.
6. Infusion pump and indwelling catheter: The infusion pump (port) is usually implanted under the chest skin, consisting of a puncture seat and an intravenous catheter system, and the materials are mainly alloys, silicone rubber and plastic, etc., which are non-ferromagnetic and weak magnetic, so it is safe to conduct MRI examination.
7. Dental implants: dental implants, fixed dentures and porcelain teeth contain metals and alloys, some even show ferromagnetism, but because the implants have been firmly fixed on the alveolar bone or glued to the corresponding joints, it has a high strength, usually in the FIELD strength of 3.0 T (including) below the MRI equipment will not move and deform, but there will be artifacts in the part.
8. IUD and breast implants: Metal IUD is generally made of copper, which can be tested for MRI below 3.0 T (inclusive), but there may be local artifacts. Most of the implants used in breast plastic surgery and breast augmentation are non-ferromagnetic substances, and it is safe for these patients to undergo MRI, and a few accessories may have metals, so be aware.
9. Coronary and peripheral vascular stents: Almost all coronary artery stent products on the market are safe during MRI and can be checked on MR devices below 3.0 T (inclusive). Peripheral arterial stents prior to 2007 may have been magnetically weak, but MRI is generally thought to be possible after 6 weeks of surgery.
10. Artificial heart valves and valvular forming rings: Almost all prosthetic heart valves and valvular forming rings are MRI-safe and can be examined in MR scanners below 3.0 T (inclusive) at any time after surgery.
11. Intraocular implants: Magnetic intraocular implants, which may be displaced in a strong magnetic field, such patients should not undergo MRI examination.