Researchers at Imperial College London have developed a prototype mini MRI scanner that fits around a patient’s leg
In a proof-of-concept study using animal knees, the results suggest the technology could be used to show all the structures of the knee.
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.
The development of the ‘mini’ MRI scanner was funded by the National Institute for Health Research.
Currently, key components of the knee joints such as ligaments and tendons are difficult to see in detail in the MRI scans, explains Dr Karyn Chappell, a researcher and radiographer from Imperial’s MSK Lab: “Knee injuries affect millions of people – and MRI scans are crucial to diagnosing the problem, leading to quick and effective treatment. However we currently face two problems: connective tissue in the knee is unclear on MRI scans, and people are waiting a long time for a scan.”
Dr Chappell added: “This can cause particular problems for women, as they are at greater risk of anterior cruciate ligament injuries. The reasons for this are unclear, but it could be linked to hormones such as oestrogen making ligaments more elastic, leading to more joint injuries.”
Knee injuries commonly affect one of three areas: the tendons, the meniscus, or the ligaments. 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. This is because they are made mostly of the protein collagen, arranged as fibres.
The collagen fibres hold water molecules in a tight configuration, and it is in fact water that is detected by the MRI. If you do see a signal it suggests there is more fluid in the area – which suggests damage, but it is very difficult for medical staff to conclusively say if there is injury.”
To overcome this problem, Dr Chappell harnessed the power of a phenomenon called the ‘magic angle’. She said: “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.
“Previously, the magic angle phenomenon was thought of as a problem, as it could mean medical staff mistakenly thinking the knee is injured. However, I realised that i