Super scans

Oxford Instruments is working with a superconductor specialist to develop a new generation of MRI scanners.


Oxford Instruments

is working with a superconductor specialist to develop a new generation of MRI scanners that will give doctors far more information about their patients.

The device maker’s partner, Coated Conductors Consultancy, is building a superconductor that is claimed to have an engineering current density up to 50 times greater than the next-best technology: coated-conductor tapes.

The superior energy density of the proposed superconductors will enable medical staff to scan patients lying on a bed rather than in cramped chambers.

A series of superconductors each the length of a can of baked beans, placed under the bed, will provide doctors with better images than they get from existing MRI scanners, said Dr Ian McDougall, Oxford Instrument’s intellectual property manager.

‘What we are interested in is the profile of the field,’ he said. MRI scanners produce static magnetic fields. Because scanners using the new superconductors could control the magnetic field of each ‘bean can’ individually, doctors would be able to manipulate the overall field to obtain a much better image.

The devices should also cost less to use than existing technology, he said. The estimated 20,000 MRI scanners in use around the world use low-temperature superconductivity.

They are cooled by liquid helium, which has a boiling point of 4.2K, confining devices to specialised departments in hospitals.

The coated-conductor cylinders that Oxford Instruments is examining, however, use high-temperature superconductivity. This means the liquid nitrogen used to cool the superconductors has a boiling point of 77K and is relatively cheap to transport.

The development could lead to a new generation of medical devices that can be moved outside specialised sites, meaning new uses for the scanners are likely to be adopted. The industry is interested in adding elements to the scanners that would indicate particular complaints, McDougall said.

Coated Conductors Consultancy (3-Cs) holds two patents to manufacture superconductors by applying a liquid film rather than using tape or wire. 3-Cs plans to apply three layers of film to a cylindrical former through which the liquid nitrogen is passed. An insulator, a superconductor and a metal, which will usually be gold or silver, will be applied to the former.

Coated cylinders give manufacturers much greater control over the application of the layers. Superconductors manufactured using tape can easily be 10–20m long. The coated cylinders may be rotated while the layers are being applied, leading to a finer degree of control than previously possible.

3-Cs’s managing director, Eamonn Maher, said: ‘You take a bean can and rotate it — it’s like roasting a chicken on a spit.’

The rival technology, coated-conductor tape, is being developed in laboratories. The manufacturing process, however, often results in cracks or flaws in the tape because, on average, the tape is reeled and unreeled 17 times during the construction of the superconductor. Even if the coated-conductor tape is wound on to the cylindrical former successfully, the thickness of the tape makes the current density far lower than the coated-conductor cylinder.

The coated-conductor tape’s current density — its electrical current divided by its total cross-sectional area — is up to 50 times less than 3-Cs’s new method. ‘We have got another factor of 10 or 50 on top of the tape,’ said Maher.

The technology could also be used to improve energy generation and distribution efficiency, and in Maglev trains.

3-Cs is being given assistance by the National Metals Technology Centre (Namtec). The company has received funding from the DTI, but is hoping to find further investment to continue developing the technology.

Superconducting electrical machines are usually designed in the same way as conventional machines operating at normal temperatures – with long lengths of conductor wound into coils.

However, suitable lengths of high temperature superconducting tape are not yet available for building other than relatively simple demonstration equipment and this is likely to remain the case for some years to come.

The 3-C’s concept eliminates the need for long lengths of conductor and uses film deposition and lithographic techniques widely used in the semiconductor industry, but in three dimensions. The superconducting layers are deposited directly onto cylindrical formers. Superconducting tracks are then patterned using, for example, laser scribing or etching of the superconducting layer. In this way multilayer superconducting structures will be built up directly into the cylindrical geometry required by the final electrical machine.