Milestone-Proposal:Active shielding of superconducting magnets

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Docket #:2018-04

This Proposal has been approved, and is now a Milestone


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:

1961 to 1989

Title of the proposed milestone:

The active shielding of Superconducting MRI Magnets (1984-87)

Plaque citation summarizing the achievement and its significance:

At this site between 1986 and 1987 the first actively shielded superconducting magnet suitable for practical Magnetic Resonance Imaging (MRI) use was engineered, designed and produced. Part of a series of superconducting magnet developments by Oxford Instruments/Siemens this innovation reduced the size and weight of installations decreasing total system cost, allowing machines to be more flexibly located and facilitating easier transportation thus benefiting advanced medical diagnosis all over the world.

200-250 word abstract describing the significance of the technical achievement being proposed, the person(s) involved, historical context, humanitarian and social impact, as well as any possible controversies the advocate might need to review.


IEEE technical societies and technical councils within whose fields of interest the Milestone proposal resides.


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):


IEEE Organizational Unit(s) arranging the dedication ceremony:

Unit: LMAG, UK & Ireland Section Region 8
Senior Officer Name: Mike Hinchey

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

IEEE Section: Superconductivity Council
IEEE Section Chair name: Dr Bruce Strauss

Milestone proposer(s):

Proposer name: Roderick I Muttram
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 in decimal form 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.

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)? If personal names are included in citation, include justification here. (see section 6 of Milestone Guidelines)

Magnetic Resonance Imaging has become the imaging method preferred by clinicians and patients alike. Utilising strong magnetic fields and weak radio waves, it can produce extraordinarily clear images of the internal organs of the body. It 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). MRI is a non-invasive, painless procedure that can eliminate the need for exploratory surgery. It carries no risk of prolonged exposure to the ionising radiation that is inherent in other techniques, such as Computed Tomography (CT), which are based on X-rays. The patient is moved into the scanner on a couch that carries the low power Radio Frequency (RF) coils wrapped around the parts to be imaged. For most people, there is no sensation of the RF or of the powerful magnetic field in the scanner bore. They hear the pulsing of image-localising gradient magnetic fields superimposed on the main field during the scan, which takes anything from a few minutes to an hour or more, during which time they can talk to the radiographer in charge of the MRI procedure.

MRI enables the safe visualisation of soft tissue at any point in the body. Its application in both routine diagnosis and in research is extensive, but principal uses include:

Diagnosis of tumours, including those in the brain and pituitary gland Diagnosis of multiple sclerosis Diagnosis of infections in the brain, spine and joints Imaging of damaged ligaments in the wrist, knee and ankle, and of shoulder injuries Diagnosing tendonitis Evaluating masses in soft tissue Evaluating spinal bone tumours, cysts or herniated discs Diagnosing strokes, even at their earliest stages Studies of the vascular system Exploring brain function disorders

There are around a trillion, trillion, trillion water molecules in the human body. Each molecule of water (H2O) includes two hydrogen atoms, the nucleus of each of which is a single spinning proton that behaves like a tiny magnet that aligns with an applied magnetic field, just as a compass points in the direction of the Earth’s magnetic field. The alignment is not complete, however, and the axis of proton or nuclear spin wobbles or precesses about the magnetic field direction, rather like a spinning top or gyroscope does in the Earth’s gravitational field. The precession rate is dependent on the magnetic field strength; for every one Tesla, the protons in the hydrogen atoms of the water molecules in our living tissue precess at precisely 42.6 million times per second – i.e., at 42.6MHz.

When radio waves in the form of low power Radio Frequency (RF) pulses of electromagnetic energy are shone from a transmission coil close to the body, and at exactly the same frequency as the precession rate of those protons, some of the RF energy is absorbed by the protons, altering their precession dynamics. This is known as resonance. When the RF pulses switch off, the protons recover to their initial state, re-emitting RF energy at that same resonant frequency, which is picked up by a radio reception antenna and computer analysed. The duration of the recovery period differs between normal and abnormal tissue, permitting the detection of abnormal tissue such as tumours. The RF energy emitted by each resonant nucleus is miniscule, but there are so many nuclei involved that a viable signal is produced.

By superimposing a second precisely controlled but much weaker variable magnetic field – the gradient field - on to the strong field generated by the MRI magnet, the region of the body which is at the correct magnetic field for resonance can be focused into a layer or slice as thin as a few millimetres. As the gradient field slides through the body, so a stack of these slices can be imaged to complete the scan along one of the main x, y, z axes. A full three axes scan of the head, for example, can be completed in a few minutes with a high field MRI scanner. The detail is provided by the variation in density of the water molecules in the different tissues, and by the variation in recovery period for different tissues, and can be clearer than a slice of tissue prepared as a microscope slide, but without the surgical procedure.

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) are 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. The original key developments have already 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. 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 Systems. We therefore proposing that this milestone be focused on the third major element that has enabled the widespread and flexible adoption of these machines - Active Shielding which was developed at the Eynsham site with the first actively shielded magnet completed in 1986 leading to the first MRI machine deployment at 1.5 Tesla in 1989. Earlier MRI machines needed to be installed in an iron (or other magnetic material) enclosure to to contain the stray fields from these powerful magnets to a defined area to prevent any unwanted effects. These enclosures were very heavy, meaning that machines normally needed to be installed on massive foundations at ground floor level, it also meant that machines were difficult to deliver and subsequently moved. Active shielding uses another superconducting winding to suppress and control the stray fields from the primary superconducting magnet. This has reduced the weight of such machines such that they can usually be installed where a hospital/medical facility chooses, including on higher floors and machines can easily be delivered even by air freight. This has allowed many more machines to be installed at existing medical sites significantly improving access to these machines for clinicians and patients. MRI is now one of the fundamental diagnostic tools on which modern medicine depends.

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

These actively shielded magnets combine outstanding knowledge and exploitation of materials, physical principles (including magnetics and cryogenics as well as superconductivity), electronic controls, mechanical engineering and manufacturing technology. The forces involved in such a structure are very large and a small rise in temperature can cause the superconducting circuit 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. Oxford Magnet technology have also been leaders in the development of the conductors themselves.

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). Whilst there was some prior art in active shielding which is cited in the patent 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 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.

Supporting texts and citations 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 chapters in scholarly books. 'Scholarly' is defined as peer-reviewed, with references, and published. 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. All supporting materials must be in English, or accompanied by an English translation.

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

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).

Please recommend reviewers by emailing their names and email addresses to ieee-history@ieee.org. Please include the docket number and brief title of your proposal in the subject line of all emails.