Milestone-Proposal:Active shielding of superconducting magnets


To see comments, or add a comment to this discussion, click here.

Docket #:2018-04

This proposal has been submitted for review.


To the proposer’s knowledge, is this achievement subject to litigation? No

Is the achievement you are proposing more than 25 years old? Yes

Is the achievement you are proposing within IEEE’s designated fields as defined by IEEE Bylaw I-104.11, namely: Engineering, Computer Sciences and Information Technology, Physical Sciences, Biological and Medical Sciences, Mathematics, Technical Communications, Education, Management, and Law and Policy. Yes

Did the achievement provide a meaningful benefit for humanity? Yes

Was it of at least regional importance? Yes

Has an IEEE Organizational Unit agreed to pay for the milestone plaque(s)? Yes

Has an IEEE Organizational Unit agreed to arrange the dedication ceremony? Yes

Has the IEEE Section in which the milestone is located agreed to take responsibility for the plaque after it is dedicated? Yes

Has the owner of the site agreed to have it designated as an IEEE Milestone? Yes


Year or range of years in which the achievement occurred:

1986 to 1989

Title of the proposed milestone:

The active shielding of Superconducting Magnets for MRI (1986-89)

Plaque citation summarizing the achievement and its significance:

At this site, between 1986 and 1989, the first actively shielded superconducting magnets suitable for practical Magnetic Resonance Imaging (MRI) use were engineered, designed and produced. Active shielding reduced the size, weight, and installed cost of MRI systems allowing machines to be more easily transported and flexibly located benefiting advanced medical diagnosis all over the world.

In what IEEE section(s) does it reside?

UK and Ireland Section of Region 8.

IEEE Organizational Unit(s) which have agreed to sponsor the Milestone:

IEEE Organizational Unit(s) paying for milestone plaque(s):

Unit: UK & Ireland Section
Senior Officer Name: Senior officer name masked to public

Unit: IEEE Superconductivity Council
Senior Officer Name: Senior officer name masked to public

IEEE Organizational Unit(s) arranging the dedication ceremony:

Unit: LMAG, UK & Ireland Section Region 8
Senior Officer Name: Senior officer name masked to public

IEEE section(s) monitoring the plaque(s):

IEEE Section: LMAG, UK & Ireland Section Region 8
IEEE Section Chair name: Section chair name masked to public

Milestone proposer(s):

Proposer name: Proposer's name masked to public
Proposer email: Proposer's email masked to public

Please note: your email address and contact information will be masked on the website for privacy reasons. Only IEEE History Center Staff will be able to view the email address.

Street address(es) and GPS coordinates of the intended milestone plaque site(s):

Siemens Magnet Technology, Wharf Road, Eynsham, Oxfordshire, United Kingdom. OX29 4BP.GPS coordinates: 51.777878, -1.363863

Describe briefly the intended site(s) of the milestone plaque(s). The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque.

Please give the address(es) of the plaque site(s) (GPS coordinates if you have them). Also please give the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. If visitors to the plaque site will need to go through security, or make an appointment, please give the contact information visitors will need. It is intended to place the plaque at Siemens Magnet Technology in Eynsham, a corporate site still very much at the forefront of this technology. The site is the one where the original work was done, albeit the site has grown and expanded since then.

Are the original buildings extant?

Yes in part.

Details of the plaque mounting:

It is intended to mount the plaque in the ground floor entrance hall of the site or on an external wall adjacent to the entrance.

How is the site protected/secured, and in what ways is it accessible to the public?

The site is a significant design and manufacturing location and is staffed on a 24/7 basis throughout the year. The site is in a semi-rural location so visiting will generally be by arrangement although the plaque will be seen by the significant number of industry and student visitors who come and go to the site on most days. Current contact is Simon Calvert the company's Head of Product Definition and Innovation and Chief Technology Officer; if the milestone is approved it is likely Siemens will appoint an administrator/coordinator for any visits specifically to see the Plaque.

Who is the present owner of the site(s)?

Siemens Magnet Technology Ltd., part of Siemens Healthcare

What is the historical significance of the work (its technological, scientific, or social importance)?

This proposed milestone concerns the development of practically realisable actively shielded superconducting magnets. This work has had huge significance by enabling the much more widespread adoption of MRI (Magnetic Resonance Imaging) by lowering overall system costs and allowing the installation of such machines without requiring hospitals to be built or re-built around them. This has significantly contributed to MRI becoming the imaging method preferred by clinicians and patients alike. MRI has revolutionised diagnosis and monitoring of many conditions and been of immense benefit to humanity (and even to the treatment of animals in certain cases). For a detailed description of MRI see: http://www.siemens.co.uk/en/about_us/index/manufacturing/about.htm

The company now known as Siemens Magnet Technology has been a pioneer of the magnet technology that underpins MRI machines. The invention of the superconducting magnet (1961) and the development of a superconducting magnet large enough to allow a human body to be placed inside it (1980) were in themselves key enablers of this truly game changing medical technology. Whilst MR imaging is possible with a resistive magnet the resolution of the images is insufficient to be really useful. 1.5 and 3 Tesla magnets are now common and Siemens Magnet Systems have recently developed a 7T magnet which was runner up for the prestigious UK Royal Academy of Engineering MacRobert Award in 2016. A magnet of that size would be virtually impossible to realise without active shielding for the reasons set out in the section below. The original key developments have been recognised and commemorated in several ways including with a 'blue plaque' (although not an IEEE milestone plaque) at the site where they were carried out (the former Oxford Instruments site in Oxford UK); unfortunately this site now has no connection with the business and no engineering activity so a milestone plaque at that site would not get useful exposure.

A subsidiary (Oxford Magnet Technology) was formed in 1982 and a new site was built at Eynsham, Oxfordshire in 1984, Siemens was a key client and acquired first a 51% share and bought the remaining 49% of the JV in 2003 and the business became Siemens Magnet Technology. Active Shielding was developed at that site and this is considered to be the best location of a Milestone Plaque as it will not only commemorate this game changing technology but will also get exposure to engineers working in the field and students visiting the site giving maximum visibility both to the achievement and to the IEEE.

At the time of the development of Active Shielding the Company was known as Oxford Magnet Technology, this later became Siemens Magnet Systems. The patents are in the name 'Oxford Advanced Technology Ltd' which was the name of the OMT legal entity at that time.

MRI is now one of the fundamental diagnostic tools on which modern medicine depends. Active Shielding was a key enabler to MRI becoming so widespread and important, with annual sales/installations of such machines increasing from a few units a year to over a 1000 units a year from the Eynsham site today. Truly a technology that has benefited all mankind.

The key people involved in the development were:

· John Woodgate (OMT Managing Director) – deceased · David Hawksworth (OMT Engineering Director and later Managing Director) – deceased · John Bird (Magnet Engineer responsible) · Frank Davis (Technical Director)

Siemens Magnet Technology is believed to still be in contact with Frank Davis

What obstacles (technical, political, geographic) needed to be overcome?

Prior to the development of actively-shielded magnets, MRI scanners were very difficult to site in hospitals as the general exposure limit for static magnet fields is just 5 gauss. Above this level, some members of the population, such as pace-maker wearers, have to be excluded.

To reduce the 5 gauss contour to an acceptable level, many Tonnes of ferrous shielding were required. The requirement for this passive shielding greatly increased the construction costs and installation lead-time and severely restricted where machines could be sited, largely restricting them to ground floors where suitable load bearing foundations could be provided.

In addition, the interaction of ferrous materials in the vicinity of the scanner with the very high stray magnetic fields substantially affected parameters such as field uniformity which are important to image quality. In many cases, ferrous re-bars in the floor had to be replaced with non-magnetic reinforcement to avoid a detrimental effect on the magnet, further increasing construction costs and disruption in the case of installation in existing hospitals or clinics.

Actively-shielded magnets eliminate or substantially reduce the above issues enabling lower installed cost and substantially reducing the lead-time for the installation of an MRI scanner. Without this innovation 3T and 7T magnets which enable significantly improved image resolution and thus diagnostic capability would be all but impossible to realise.

As a result, the Active shielding technology pioneered by OMT, has now become the industry-standard approach.

The detail of why the Active shielding techniques developed by OMT were practically realisable whereas the prior art cited was not is set out in the attached patents and will not be repeated here.

Suffice it to say that these actively shielded magnets combine outstanding knowledge and exploitation of materials, physical principles (including magnetics and cryogenics (-269°C (4.2 Kelvin) must be sustained just 30mm inside the room temperature exterior) as well as superconductivity), electronic controls, mechanical engineering and precision manufacturing. The internal forces involved are very large (circa 380 tonnes in a 3T magnet) and a small rise in temperature can cause the both the main and/or the shielding superconducting circuits to 'quench' dissipating enough energy to destroy the machine if not properly controlled. Large structures must be manufactured, and windings fabricated and supported all to very high degrees of accuracy (Field Uniformity is dependent on <100µm positional accuracy of the coils).

Oxford Magnet Technology/Siemens Magnet Technology have also been leaders in the development of the conductors themselves which were another enabling factor.

What features set this work apart from similar achievements?

Early Superconducting magnets used heavy and expensive iron shielding to reduce the level of stray fields which have undesirable effects on other equipment (e.g. pacemakers) as detailed above.

Whilst there was some prior art in active shielding which is cited in the patents the earlier work did not produce techniques suitable for the high field strengths needed for NMR/MRI nor would it readily accommodate changes to the bore field strength which are sometimes required. The Oxford Advanced Technology work led to techniques which could be realised in production volumes and led to stable outcomes through the ranges required. As has been said this led to machines which were lighter, cheaper, easier to transport and more flexible in terms of possible location making MRI much more widely available, benefiting huge numbers of people.

References to establish the dates, location, and importance of the achievement: Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or citations to pages in scholarly books. You must supply the texts or excerpts themselves, not just the references. At least one of the references must be from a scholarly book or journal article.

The US and European Patents are attached: US4587504, filed Nov 7th 1984, granted 6th May 1986 Media:US4587504.pdf and EP144171B, Filed 9th Nov 1984, granted 31 Jan 1990 Media:EP144171B1.pdf Patents are public documents.

Other supporting documents are: 00133510, IEEE TRANSACTIONS ON MAGNETICS, VOL. 27, NO. 2, MARCH 1991; A 2-TESLA ACTIVE SHIELD MAGNET FOR WHOLE BODY IMAGING AND SPECTROSCOPY 01065051, IEEE TRANSACTIONS ON MAGNETICS, VOL. MAG-23, NO. 2, MARCH 1987; CONSIDERATIONS IN THE DESIGN OF MRI MAGNETS WITH REDUCED STRAY FIELDS 01063856, IEEE TRANSACTIONS ON MAGNETICS, VOL. MAG-21, NO. 2, MARCH 1985; PRESENT STATUS OF MRI MAGNETS at OXFORD - useful in its description of earlier shields using Iron weighing 20T for a 1Tesla magnet 00402514, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 5, NO. 2, JUNE 1995: Trials and triumphs of superconductivity: The making of Oxford Instruments - useful background on the overall contribution of the Oxford Instruments/Siemens team up to that date. The copyright in all of these lies with the IEEE and they are normally subject to a charge - they will therefore be submitted by email.

Contemporary brochure on actively shielded magnets issues by Oxford in the mid 1980's Media:20180724192657.pdf

Slides from Siemens Magnet systems showing the position of Active Shielding within the timeline of Superconducting MRI Magnet developments and the growth in delivered volumes. The mid 1990's dip was a US market issue affecting all manufacturers Media:OMT developments and sales growth.pdf

Supporting materials (supported formats: GIF, JPEG, PNG, PDF, DOC): All supporting materials must be in English, or if not in English, accompanied by an English translation. You must supply the texts or excerpts themselves, not just the references. For documents that are copyright-encumbered, or which you do not have rights to post, email the documents themselves to ieee-history@ieee.org. Please see the Milestone Program Guidelines for more information.


Please email a jpeg or PDF a letter in English, or with English translation, from the site owner(s) giving permission to place IEEE milestone plaque on the property, and a letter (or forwarded email) from the appropriate Section Chair supporting the Milestone application to ieee-history@ieee.org with the subject line "Attention: Milestone Administrator." Note that there are multiple texts of the letter depending on whether an IEEE organizational unit other than the section will be paying for the plaque(s).