Magnetic Resonance Imaging (MRI) of the brain is a sophisticated diagnostic tool that creates highly detailed pictures of the internal structures of the head. The technology uses a very powerful magnet and radio waves to align and excite the hydrogen protons. The scanner detects the energy released as these protons return to their normal alignment, converting this into a digital image. This non-invasive method provides clear differentiation between tissues, making it invaluable for diagnosing neurological conditions. Proper preparation is paramount to ensure both patient safety and the clarity of the resulting images.
Do Not Wear or Bring External Metal
The environment inside the MRI suite is defined by an extremely strong magnetic field that is always active, posing a significant risk to anything containing iron or other ferromagnetic materials. Preparation involves removing all removable, external metal from the body and clothing. This includes obvious items like watches, rings, earrings, necklaces, and body piercings, which can be pulled toward the machine or cause severe burns due to induced currents.
Patients must also avoid wearing clothing that contains metal components, such as zippers, snaps, belt buckles, or underwire in bras, often requiring a change into a facility-provided gown. All personal accessories, including keys, coins, hairpins, and electronic devices like cell phones, must be left outside the controlled magnetic area. Even less obvious items can cause problems, including certain cosmetics, hair products, and temporary tattoos.
Some makeup, especially mascara and eyeliner, and certain tattoo inks, particularly black and dark colors, contain metallic pigments like iron oxides. These microscopic metal flakes can interact with the magnetic field, causing localized heating, tingling, or a temporary burning sensation on the skin. Additionally, these metallic compounds can create artifacts that distort the image, potentially obscuring the area being examined.
Do Not Conceal Internal Medical History
A comprehensive safety screening process is necessary because non-removable metal within the body presents a serious hazard inside the scanner. Patients must disclose all surgical history and implanted medical devices, as failure to do so can result in severe injury or device malfunction. The static magnetic field can exert a forceful pull or torque on ferromagnetic implants, and radiofrequency pulses can induce currents that cause tissue heating around wires or leads.
Absolute contraindications that must be disclosed include:
- Older, ferromagnetic cerebral aneurysm clips.
- Most cardiac devices, such as pacemakers and implantable cardioverter-defibrillators.
- Cochlear implants.
- Certain neurostimulators and implanted drug infusion pumps.
The magnetic field can irreversibly damage electronic components or cause the device itself to move.
While many modern implants are labeled as “MR-conditional” or “MR-safe,” this designation requires specific documentation to confirm safety under certain magnetic field strengths and scan parameters. Patients with metallic foreign bodies, such as shrapnel, bullet fragments, or metal filings in the eye, must also be thoroughly evaluated. The powerful magnetic field could cause these fragments to move, leading to tissue damage or blindness.
Do Not Move During the Scan
Movement remains the primary factor that compromises the quality of a brain MRI. The scanning process relies on collecting data over several minutes for each image sequence. Any motion, even slight head shifts or involuntary movements, introduces artifacts like blurring or “ghosting” into the image data.
When motion artifacts are significant, the resulting images may be deemed non-diagnostic, meaning they cannot be reliably interpreted by the radiologist. This necessitates repeating parts of the scan, which prolongs the examination time and increases patient inconvenience. Patients are instructed to remain as still as possible, sometimes for ten minutes or more, and to breathe normally without moving their head.
For brain MRIs requiring a contrast agent, patients are often asked to fast for four to six hours before the appointment. This preparation reduces the risk of nausea or vomiting, which can occur as a reaction to the contrast injection. Anxiety or claustrophobia can also lead to movement, so patients who anticipate difficulty remaining still should discuss sedation options with their doctor beforehand.