What Is An Mri Scan?

  • Kate Imogen Watson Bachelor of Science - BS, Biomedical Sciences, General, Newcastle University

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Healthcare providers may recommend magnetic resonance imaging (MRI) to help diagnose or monitor a variety of conditions. Over 3,000,000 MRI scans were performed by the NHS in 2022.1 This scan helps in producing precise images and does not cause pain. 

Images are formed using magnetic fields and radio waves. MRI scans don’t use X-rays so they are a common choice for individuals who need frequent imaging as they do not use radiation. There are different types of MRI scans and these can be used to look at different structures within the body from the brain to pelvic organs. MRIs are generally safe if proper safety guidelines are maintained.

There are many reasons to be referred for an MRI. The procedure may be slightly uncomfortable for patients but there are many considerations made that can ease discomfort. There are safety guidelines in place to keep the safety risk very low. 

Reasons for getting an MRI scan 

MRI scans can examine almost any part of the body to help diagnose and monitor conditions. If a condition is undiagnosed an MRI can provide information to aid diagnosis. MRIs can be used to monitor conditions over a period of time. Additionally, MRIs can assess the effectiveness of treatment by having frequent scans throughout treatment. Parts of the body that MRIs can examine include:

  • The brain and spinal cord
  • Breasts
  • Heart and blood vessels
  • Internal organs
  • Bones and joints

Brain and spinal cord MRIs can evaluate and diagnose conditions such as brain aneurysms, tumours, multiple sclerosis, spine anatomy and alignment, and stroke

Cardiac (heart) MRIs can be used to evaluate the anatomy and function of various parts of the heart, diagnose cardiovascular conditions, and evaluate the effects of coronary artery disease

Body MRIs can look at tumours in your chest, abdomen, or pelvis, liver diseases, inflammatory bowel disease, malformations and inflammation of blood vessels, and developing foetuses. 

MRIs of bones and joints can evaluate bone infections, tumours, disc abnormalities, and joint issues caused by injuries. 

Breast MRIs can be used to detect breast cancer in individuals who have dense breast tissue or may be at high risk of breast cancer. 

Many other conditions not mentioned above can be assessed using MRI as well. 

How it works

MRIs use powerful magnets to produce a strong magnetic field. The protons in the body align with this magnetic field. Then radio waves are pulsed through the patient which causes the protons in the body to pull against the magnetic field. 3,4

When the radio waves are turned off, MRI sensors can detect the energy released as the protons realign with the magnetic field. The time it takes to realign and the amount of energy released can provide information on the various types of tissue (such as water and fat). 

Multiple radio waves can be used to visualise particular structures in the body. Typically diseases can cause an increase in water content so an MRI can use this characteristic to detect diseases.2 The computer uses the signals produced to make digital images.

What happens during an MRI

Before the scan, the patient will be asked to remove anything with metal that could come loose, this could be jewellery or underwear with a metal wire in it. Then the patient will lie on a flat bed which is moved into the scanner. The patient is positioned in the scanner feet first or head first depending on which part of the body is being investigated, 

The procedure is carried out by a radiographer who leaves the room once the patient is placed into the scanner, the computer is used to control the scanner. The radiographer and patient can communicate through an intercom and the radiographer can see the patient through a window or television monitor. If a patient feels anxious about anything throughout the procedure they can speak to the radiographer who will be able to reassure them and talk through the process. 

MRI scans are very loud so patients may be given earplugs or headphones to wear. The patient needs to stay as still as possible during the scan to try to provide the clearest image possible. The duration of the scan depends on the size of the area being scanned and the amount of images being taken but it can last between 15-90 minutes. 

Open MRI

The most commonly used MRI machines are closed MRI machines. These are a narrow tube in which the patient is surrounded by magnets. Open MRI machines typically have two flat magnets positioned over and under you with a large space in between. 

Open MRIs may be a better option for claustrophobic patients as it has open space on each side. This is compared to the confined space patients are in for a closed MRI. Studies found that claustrophobic patients preferred open MRIs to other MRIs, including short MRIs (closed MRIs which are shorter in length).5 Unfortunately, open MRI’s images aren’t as clear as closed MRI’s so it may not always be an option for patients.

MRI with contrast

An MRI with contrast is where a contrast material is administered before the scan. This is administered through an intravenous (IV) injection. This can be uncomfortable whilst the needle is in but the discomfort doesn’t last for long. In some rare cases, patients who have contrast material can experience side effects. These include:

  • Nausea
  • Pain at the site of injection
  • Headache
  • Hives, itchy eyes or other signs of an allergic reaction

Safety

MRIs are considered to be one of the safest medical procedures available and are considerably safer than X-rays as there is no radiation. There is a slight risk of having an allergic reaction to contrast material if it's administered but healthcare providers can treat it immediately. 

Radiologists are aware of all safety risks for the procedure such as medical equipment that can be pulled towards the magnets.Some metal implants may not be MRI-safe. Examples of devices that may not be MRI-safe are: 

Before an MRI a healthcare provider will get a medical history including a list of medical devices and implants. Some devices will be certified as MRI-safe. MRI as a procedure might not be suitable If a patient has a medical device that isn’t MRI-safe.

If the patient is pregnant their healthcare provider will assess whether it is suitable for them to have an MRI scan or not. Research has found that MRI does not pose any known risks to the foetus although gadolinium-based contrast agents may pose a risk. However, it is important to note there isn’t much data on the long-term effects of MRI on foetuses.7

Summary

MRI scans can be performed to diagnose many conditions or monitor conditions/ effectiveness of treatments. MRIs produce precise images of internal structures and organs such as the brain, blood vessels, breasts, and bones. They can assess various conditions in nearly any part of the body. Images are produced by stimulating the body’s protons using radio waves and large magnets. A computer can turn this information into an image. 

During an MRI, patients are expected to lie as still as possible on a flatbed and a radiologist stays in contact with them. Closed MRIs can be claustrophobic for patients. Open MRIs have a magnet above and below the patient instead of a narrow tube surrounding the patient so they can be better for claustrophobic patients. MRIs sometimes require a contrast material to be administered to patients via an IV. 

MRIs are one of the safest medical procedures to receive. Radiologists are aware of safety precautions necessary and patients with certain metal implants may not be able to receive MRIs. Pregnant patients’ suitability for an MRI will be discussed with healthcare providers. Data suggests MRIs (not including MRI with contrast) are safe for pregnant patients but longitudinal data is limited. 

References

  1. Lawal O, Regelous P, Omiyi D. Supporting claustrophobic patients during Magnetic Resonance Imaging examination– the patient perspective. Radiography [Internet]. 2023 [cited 2024 Sep 5]; 29(6):1108–14. Available from: https://linkinghub.elsevier.com/retrieve/pii/S107881742300175X.
  2. Berger A. Magnetic resonance imaging. BMJ [Internet]. 2002 [cited 2024 Sep 5]; 324(7328):35. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1121941/.
  3. Grover VPB, Tognarelli JM, Crossey MME, Cox IJ, Taylor-Robinson SD, McPhail MJW. Magnetic Resonance Imaging: Principles and Techniques: Lessons for Clinicians. J Clin Exp Hepatol [Internet]. 2015 [cited 2024 Sep 5]; 5(3):246–55. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4632105/.
  4. Moser E, Stadlbauer A, Windischberger C, Quick HH, Ladd ME. Magnetic resonance imaging methodology. Eur J Nucl Med Mol Imaging [Internet]. 2009 [cited 2024 Sep 5]; 36(1):30–41. Available from: https://doi.org/10.1007/s00259-008-0938-3.
  5. Iwan E, Yang J, Enders J, Napp AE, Rief M, Dewey M. Patient preferences for development in MRI scanner design: a survey of claustrophobic patients in a randomized study. Eur Radiol [Internet]. 2021 [cited 2024 Sep 5]; 31(3):1325–35. Available from: https://link.springer.com/10.1007/s00330-020-07060-9.
  6. Mittendorff L, Young A, Sim J. A narrative review of current and emerging MRI safety issues: What every MRI technologist (radiographer) needs to know. J of Medical Radiation Sci [Internet]. 2022 [cited 2024 Sep 5]; 69(2):250–60. Available from: https://onlinelibrary.wiley.com/doi/10.1002/jmrs.546
  7. Lum M, Tsiouris AJ. MRI safety considerations during pregnancy. Clinical Imaging [Internet]. 2020 [cited 2024 Sep 5]; 62:69–75. Available from: https://linkinghub.elsevier.com/retrieve/pii/S0899707120300553.

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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Kate Imogen Watson

Bachelor of Science - BS, Biomedical Sciences, General, Newcastle University

Kate is a Biomedical Sciences graduate from Newcastle University with years of scientific writing experience. Through her studies, she has gained a great amount of knowledge on the science behind pathology and healthcare. Kate has had a placement with a PR company and studied science communication whilst at university. Also whilst at university, she contributed to the medical school’s blog by publishing articles. Kate’s previous research focuses on government strategies of health promotion and food inequality and health. With a strong interest in health communication, she is currently working on improving her skills and experience whilst exploring options for further studies.

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