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Researchers at Imperial College London have developed a prototype mini MRI scanner that fits around a patient’s leg. The team say the device — which uses so-called ‘magic angle’ effect — could potentially help diagnose knee injuries more quickly, and more accurately.

The scientists say the device (which looks like a large metal ring through which a patient places their leg) could help diagnose conditions such as anterior cruciate ligament injuries — particularly common among footballers. Furthermore, the small size of the device could enable it to be used in local clinics and even GP surgeries, potentially reducing NHS waiting times for MRI scans.

Currently, key components of the knee joints such as ligaments and tendons are difficult to see in detail in the MRI scans.

Knee injuries commonly affect one of three areas: the tendons (which attach muscle to bone), the meniscus (a cushioning pad of cartilage that prevents the bones of the joints rubbing together), or the ligaments (tough bands of connective tissue that hold bones in a joint together).

Following knee injury a doctor may refer a patient for a MRI scan to help establish which part of the joint is injured. MRI scans use a combination of radio waves and strong magnets to ‘flip’ water molecules in the body. The water molecules send out a signal, which creates an image.

However, tendons, ligaments and meniscus are not usually visible with MRI, due to the way water molecules are arranged in these structures, explains Dr Karyn Chappell. “These structures are normally black on an MRI scan — they simply don’t produce much signal that can be detected by the machine to create the image.

To overcome this problem, Dr Chappell harnessed the power of a phenomenon called the ‘magic angle’: “The brightness of these tissues such as tendons and ligaments in MRI images strongly depends on the angle between the collagen fibres and the magnetic field of the scanner. If this angle is 55 degrees the image can be very bright, but for other angles it is usually very dark.”

The team explain the magic angle is achieved in their scanner because they are able to easily change the orientation of the magnetic field. While the patient sits comfortably in a chair, the specially designed magnet (which uses motors and sensors similar to those found in robots in car factories) can rotate around the leg and the orientate magnetic field in multiple directions.

This is not possible in current hospital MRI scanners, which are also much more expensive than the prototype scanner.