Magnetic Resonance Imaging (MRI) – Definition & Use
Magnetic Resonance Imaging (MRI) is a diagnostic imaging technique that uses powerful magnetic fields and radio waves to produce detailed cross-sectional images of the body.
Wissenswertes über "Magnetic Resonance Imaging"
Magnetic Resonance Imaging (MRI) is a diagnostic imaging technique that uses powerful magnetic fields and radio waves to produce detailed cross-sectional images of the body.
What is Magnetic Resonance Imaging?
Magnetic Resonance Imaging (MRI), sometimes referred to as Magnetic Resonance Tomography (MRT) or historically as nuclear magnetic resonance (NMR) imaging, is an advanced medical imaging technique used widely in clinical diagnostics. Unlike X-ray or computed tomography (CT), MRI does not use ionising radiation. Instead, it relies on strong magnetic fields and radiofrequency (RF) waves to generate highly detailed, cross-sectional images of the human body. MRI is particularly well-suited for visualising soft tissues, organs, the brain, spinal cord, joints, and ligaments.
How Does MRI Work?
The physical principle behind MRI is nuclear magnetic resonance. The human body is largely composed of water, and the hydrogen nuclei (protons) within water molecules possess a property called spin. When a patient enters the strong magnetic field of an MRI scanner, these protons align along the direction of the field. Short pulses of radiofrequency waves are then applied, temporarily knocking the protons out of alignment. As the protons return to their resting state, they emit signals that are detected by receiver coils and processed by a computer to construct precise cross-sectional images.
Clinical Applications
MRI is used across a broad range of medical specialties. Common clinical applications include:
- Neurology and Neuroradiology: Imaging of the brain and spinal cord; diagnosis of stroke, multiple sclerosis, tumours, and inflammation
- Orthopaedics and Trauma Surgery: Assessment of joints, cartilage, ligaments, tendons, and muscles
- Cardiology: Evaluation of the heart and major blood vessels (cardiac MRI)
- Oncology: Detection, staging, and monitoring of tumours
- Gastroenterology and Urology: Imaging of the liver, kidneys, prostate, pancreas, and abdominal organs
- Gynaecology: Assessment of the uterus and ovaries
What to Expect During an MRI Scan
Before the examination, patients must remove all metallic objects, as the powerful magnetic field of the scanner can attract them. These include jewellery, piercings, watches, and belt buckles. Patients with certain metal implants -- such as some cardiac pacemakers, metallic aneurysm clips, or cochlear implants -- may not be eligible for MRI scanning. This must be clarified with the referring physician in advance.
During the scan, the patient lies on a motorised table and is moved into the cylindrical bore of the MRI machine. Depending on the area being examined, the scan typically takes between 15 and 60 minutes. The machine produces loud knocking and banging noises, so patients are offered earplugs or headphones. For certain examinations, an intravenous contrast agent (commonly gadolinium-based) may be administered to improve the visibility of specific structures.
Advantages of MRI
- No ionising radiation (no X-rays involved)
- Excellent soft tissue contrast and visualisation
- Three-dimensional imaging capabilities
- Multiple tissue contrasts achievable through different imaging sequences
- No radiation exposure, making it suitable for repeated use and for children
Limitations and Contraindications
- Longer scan times compared to CT or X-ray
- Higher cost and lower availability compared to other imaging modalities
- Not suitable for patients with certain metal or electronic implants
- Claustrophobia can be a challenge in closed-bore scanners; open MRI systems are an alternative
- Motion artefacts can reduce image quality
Contrast Agents in MRI
To improve the visualisation of specific tissues, tumours, or areas of inflammation, a contrast agent may be administered during the MRI examination. The most commonly used MRI contrast agents contain gadolinium, a paramagnetic metal. Gadolinium-based contrast agents are generally well tolerated, but may in rare cases cause allergic reactions. Patients with impaired kidney function should be assessed carefully, as there is a risk of a rare but serious condition called nephrogenic systemic fibrosis in this population.
MRI During Pregnancy
During the first trimester of pregnancy, MRI is generally only performed when there is an urgent medical need, as the effects of strong magnetic fields on early embryonic development are not yet fully understood. In the second and third trimesters, MRI is considered largely safe and may be used when clinically indicated. The use of gadolinium-based contrast agents is typically avoided during pregnancy.
References
- Westbrook, C., Roth, C. K., Talbot, J.: MRI in Practice. 5th edition. Wiley-Blackwell, Oxford 2019.
- European Society of Radiology (ESR): ESR Statement on the Stepwise Development of Imaging Biomarkers. Insights Imaging, 2023. Available at: https://www.european-radiology.org
- National Institute of Biomedical Imaging and Bioengineering (NIBIB): Magnetic Resonance Imaging (MRI). Available at: https://www.nibib.nih.gov/science-education/science-topics/magnetic-resonance-imaging-mri
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Related search terms: Magnetic Resonance Imaging + MRI + Magnetic Resonance Tomography + Nuclear Magnetic Resonance Imaging + NMR Imaging