Milestones:First Computerized Tomography (CT) X-ray Scanner, 1971


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Middlesex, England
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United Kingdom and Ireland
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First Computerized Tomography (CT) X-ray Scanner, 1971


On 1 October 1971, a team at the EMI Research Laboratories located on this site produced an image of a patient’s brain, using the world’s first clinical X-ray computerized tomography scanner, based on the patented inventions of Godfrey Hounsfield. The practical realization of high-resolution X-ray images of internal structures of the human body marked the beginning of a new era in clinical medicine.

Justification for including Godfrey Hounsfield's name in the Citation:

The achievement being commemorated by the plaque is in respect of first human tissue image by a practical and reproducible CT scanner designed by Godfrey Hounsfield and built by EMI. Hounsfield's fundamental role was recognised by the award of the two US patents in his name, #3778614 and #4052619 cited below, as well as by a Nobel Prize. The patents were tested in the US courts and upheld.

Whilst the Nobel prize was shared with Alan Cormack, Cormack worked independently in the United States and played no part in the EMI Labs achievement.

Street address(es) and GPS coordinates of the Milestone Plaque Sites

150 Clayton Road Hayes Middlesex England GPS: 51.50556, -0.42659, 150 Clayton Road Hayes Middlesex England GPS: 51.50556, -0.42659

Details of the physical location of the plaque

Exterior wall of Jupiter House

How the plaque site is protected/secured

Plaque will be permanently fixed to the wall.

Historical significance of the work

The EMI CT Scanner was the first machine that used computerized tomography to produce X-Ray images of the internal organs of the human body, for example the brain.

The evolution of the first practical implementation of computer-assisted tomography culminated in the X-ray scanner invented and developed by EMI Electronics on this site within its Hayes, Middlesex campus in 1970. This was the World’s first medical imaging system capable of producing high resolution detailed scans of internal body structures, such as the brain, heart, and other organs.

The mathematical basis of tomography has a long history, dating back to the early 20th century, but it was not until the advent of modern high speed computers capable of processing large data sets (such as those used in medical imaging applications) within practical time scales, that high resolution images could be obtained. Oldendorf (1963) is acknowledged to be the first to conceptualise the possibility of extracting useful data from line integrals. The work of Allan Cormack (1963) posed the question of whether it might be possible to deduce the internal structure of a solid object using external measurements under laboratory conditions. This was essentially the challenge that the EMI team set themselves to accomplish, building on the theoretical work of groups in Europe and the United States over several decades.

The work of Johann Radon (1986) and Stefan Kaczmarz (1993) had established the basic framework within which a successful imaging system could be achieved. The concept of tomographic imaging derives from the solution to the problem of reconstructing the set of values of a physical quantity along a defined path, using the data obtained from the multiple transmission of a beam of energy (e.g. light, acoustic waves, radio waves, or X-rays) through the object under investigation. The outcomes of a set of transmission measurements obtained from numerous scans performed over a 360 degree range of angles in a defined plane (or slice) form the data set from which the physical properties of the medium being investigated can be evaluated. Manipulating the data to yield accurate solutions quickly depended upon two fundamental breakthroughs. Kaczmarz (1003) demonstrated how to improve the efficiency of obtaining the solution of a large system of linear equations. Radon’s contribution was to devise the Radon Transform that became an important technique in signal processing applications. In this way, the image of a 3-dimensional opaque object can be obtained. The image is assembled slice by slice (hence the use of the word tomography, derived from the Greek word tomos, meaning ‘slice’). The resolution of the image determines the size of the data set. In clinical practice, for example, the production of a complete set of images requires the performance of a processing system that was well beyond the capability of laboratory computers, until the advent of the first mini-computers in the 1960/70s.

It was a team led by Godfrey (later Sir Godfrey) Hounsfield that began work in 1967 with the aim of applying the principles of tomography to an imaging system employing X-rays. The challenge was to produce a device that could be used safely in clinical practice. This imposed strict limits on the transmitted intensity of the X-ray beam used and the sensitivity of the receiving detection system. The first working prototype was built at EMI’s laboratories ay Hayes in 1971 and was used for brain-scanning at Atkinson-Morley Hospital in Wimbledon, London, that year. The significance of this invention to the field of medical imaging, especially of the human brain, was quickly recognised. Groups across the world began work on various developments of the original concept, as the application of computer-assisted tomography became commercially viable. The modern versions of the CT scanner, as it has become known, are installed in innumerable hospitals across the developed world, where it is used routinely for whole body, or part body, imaging of patients. The impact on clinical medicine has been immense. The technology has developed to the point where whole body scans can be completed now in less than 1 second. The EMI team achieved world –wide recognition for the 1967 invention and were granted numerous patents, some of which are referred to below. Godfrey Hounsfield received the Nobel Prize in Medicine in 1979. The Prize was awarded jointly to Allan Cormack of Tuft’s University, USA, in recognition of his seminal contributions to establishing the theoretical basis of tomography, although his ideas were not reduced to practice before Hounsfield’s team demonstrated that a feasible imaging methodology could be based on this concept.

Features that set this work apart from similar achievements

The EMI CT Scanner was the first clinical machine capable of producing high resolution images of X-ray attenuation, allowing depiction of the internal structures and organs of the human body.

Significant references

Details of the supporting texts and other reference materials are provided separately via a number of attached files. Also attached are the permissions from the site owner and the UK & Ireland Section Chair

Supporting materials

Hounsfield, G.N., "Computerized transverse axial scanning (tomography), Part I. Description of a system", British Journal of Radiology, 46, 1016-1022, 1973

Strong, A.B., Hurst, R.A.A., "Correspondence: EM1 patents on computed tomography: history of legal actions", The British Journal of Radiology, 67, 315-317, 1994

Yang, Guang-Zhong and Firmin, David N. "Retrospectroscope: The Birth of the First CT Scanner", IEEE Engineering in Medicine and Biology, January/February 2000


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