Magnetic Resonance Imaging (MRI) – Definition & How It Works
Magnetic Resonance Imaging (MRI) is a diagnostic imaging technique that uses magnetic fields and radio waves to produce detailed images of the inside of the body without using radiation.
Things worth knowing about "Magnetic Resonance Imaging"
Magnetic Resonance Imaging (MRI) is a diagnostic imaging technique that uses magnetic fields and radio waves to produce detailed images of the inside of the body without using radiation.
What is Magnetic Resonance Imaging?
Magnetic Resonance Imaging (MRI) – known in German as Kernspintomographie – is a modern, non-invasive medical imaging technique. It produces highly detailed cross-sectional images of the human body without the use of ionizing radiation such as X-rays. Instead, the procedure relies on powerful magnetic fields and radiofrequency waves. The resulting images provide high-resolution visualizations of organs, soft tissues, muscles, joints, blood vessels, and the nervous system.
How Does MRI Work?
The physical principle behind MRI is nuclear magnetic resonance (NMR). The human body contains a large number of hydrogen atoms that can be aligned by a strong magnetic field. Short radiofrequency pulses are then used to disturb this alignment. As the atoms return to their original orientation, they emit faint signals that are detected by the scanner and converted into precise cross-sectional images using complex algorithms.
During the scan, the patient lies on a movable table that slides into the cylindrical bore of the MRI machine. The procedure is painless and typically lasts between 15 and 60 minutes, depending on the area being examined. Patients are asked to remain as still as possible throughout the scan.
When is MRI Used?
MRI is used across virtually all medical specialties. Common clinical applications include:
- Neurology: Diagnosis of stroke, brain tumors, multiple sclerosis, and dementia
- Orthopedics and trauma surgery: Assessment of herniated discs, cartilage damage, meniscus tears, and fractures
- Oncology: Detection and staging of tumors in various organs
- Cardiology: Evaluation of cardiac structure and function (cardiac MRI)
- Gastroenterology: Imaging of the liver, pancreas, and intestines
- Gynecology: Visualization of the uterus and ovaries
- Vascular medicine: Magnetic resonance angiography (MRA) for imaging blood vessels
Preparation and Procedure
Before undergoing an MRI scan, patients must remove all metallic objects such as jewelry, watches, and hearing aids, as the strong magnetic field can attract or damage them. Patients with certain metal implants, pacemakers, or cochlear implants must inform the medical team in advance, as these may represent contraindications to the procedure.
In some cases, a contrast agent (usually gadolinium-based) is administered intravenously to enhance the visibility of specific structures or pathological changes. This contrast agent is generally well tolerated, but may pose risks for patients with impaired kidney function.
During the scan, loud knocking and clicking sounds are produced by the rapidly switching magnetic field gradients. Patients are therefore provided with earplugs or headphones. Individuals with claustrophobia may be offered an open MRI scanner or mild sedation.
Advantages and Limitations
The key advantages of MRI include:
- No exposure to ionizing radiation
- Excellent soft tissue contrast, especially compared to computed tomography (CT)
- Versatile application across nearly all body regions
- Capability for functional imaging (e.g., functional MRI of the brain)
The main limitations include:
- Longer scan duration compared to CT
- Higher cost and limited availability in some settings
- Restrictions for patients with certain metallic implants
- Noise and confined space can be distressing for some patients
- Motion artifacts in patients who cannot remain still
References
- Reimer, P. et al. (Eds.) – Klinische MR-Bildgebung. Springer Medizin Verlag, 3rd edition, 2010.
- World Health Organization (WHO) – Diagnostic Imaging. Available at: https://www.who.int/health-topics/diagnostic-imaging
- Lüdeke, K. M., Röschmann, P., Tischler, R. – Susceptibility artefacts in NMR imaging. Magnetic Resonance Imaging, 1985; 3(4):329–343. PubMed PMID: 4094551.
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