Magnetic Resonance Imaging (MRI) 1977 – Detailed Contrast Imaging of the Body

MRI (magnetic resonance imaging) uses magnetism, radio waves and a computer to visualise internal structures of the body. It provides greater contrast between soft tissues than X-ray images or CAT (computerised axial tomography) scans. During an MRI scan, the patient is usually placed inside a large circular tube that generates a powerful magnetic field.

If an atomic nucleus contains at least one unpaired neutron or proton, it can behave like a small magnet. A magnetic field applies a force that causes nuclei to precess or wobble like spinning tops. Increasing the external magnetic field can enlarge the energy difference between nuclear spin states. After the magnetic field is switched on, radio waves trigger transitions between spin states and place some spins in higher-energy states. When the radio wave is switched off, the spins return to a lower state (or  "relax")  and produce a detectable radio signal at the resonant frequency of the spin transition.

• In 1971, American physician Raymond Damadian suggested that MRI might be used in medical diagnosis by showing that the relaxation rates of hydrogen in water could differ between normal and malignant cells. In 1977, he performed a complete scan of the human body. 
• American chemist Paul Lauterbur contributed to producing MRI images using gradients in the magnetic field. 
• British physicist Peter Mansfield developed mathematical methods for producing images efficiently.

MRI is useful for scanning tissues containing many hydrogen nuclei (for example, in water molecules), including the brain, spinal cord, intervertebral discs and heart. Unlike X-rays, MRI does not use dangerous ionising radiation and can provide information about a tissue's chemical composition. Contrast agents (such as solutions containing the metal gadolinium) may be injected to improve image contrast. 

• Diffusion MRI  can be used to measure the diffusion of water in tissues. 
• Functional MRI  allows brain activity to be examined in real time.

Description of the article image: Dr Raymond Damadian and one of his MRI machines. Since he and his research assistants completed the first scanner more than 40 years ago, it has become an indispensable piece of medical equipment.

Historical figures mentioned in the article: Paul Christian Lauterbur (1929–2007), Peter Mansfield (b. 1933), Raymond Vahan Damadian (b. 1936)

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