50 Years of Computed Tomography (CT)

Clinical Application

The first CT scans were performed in late 1971 at Atkinson Morley’s Hospital and the results formally announced at the 32nd Annual Congress of the British Institute of Radiology, which took place on 20-21 April 1972. This announcement may be taken to be the birth date of CT. However, perhaps a more relevant date occurred in late November 1972 at the 58th Scientific Assembly and Annual Meeting of the Radiological Society of North America held at the Palmer House in Chicago.

In a Symposium; New Techniques in Radiology: Computerized Axial Tomography held in the Grand Ballroom, James Ambrose and Godfrey Hounsfield presented the method and initial clinical findings obtained by this new technique. The presentation was made to a standing room audience and effectively marked the commercial birth date of CT. The North American market in diagnostic radiology was (and still is) extremely large especially in comparison to the UK and prides itself in operating at the cutting edge of technology. Consequently, most of the major US medical schools wanted to be at the forefront of such a monumental technological revolution and multiple orders for CT scanners were generated.

EMI was a British-based, International Group of companies with an annual turnover of over £500m (or $1 billion at the exchange rate at the time). It had over 48,000 employees in 60 principal subsidiaries around the world its activities were concentrated in growth areas of electronics and the music and leisure industries. Thus, it was necessary for EMI to rapidly establish a manufacturing, marketing, installation and servicing support for the EMI-Scanner in the US and Canada.

That the commercial success of the CT Scanner stretched the company’s resources is, perhaps, an understatement.  Particularly when considering that the Scanner was EMI’s sole item of radiological equipment. On the other hand, the major suppliers of X-ray equipment (Siemens, Phillips, IGE etc) had comprehensive ranges of medical imaging equipment and well-established customer facing support mechanisms. Nonetheless EMI did develop a strong market presence based upon the CT 1010 Scanner, due to their forefront role in developing this completely new technology.

The historical development of CT during the intervening 50 years has been fully documented. Suffice to say that CT technology has had a very long shelf life, which should continue for some time. However, of some interest to the medical physics community is the historical development of scientific and technical support services to what was a completely new form of X-ray imaging.

Quality Assurance and Radiation Protection

During the 1970’s the Diagnostic Radiology Topic Group of the Hospital Physicist’s Association (HPA) was actively pursuing a programme of work to establish standard test protocols for all X-ray imaging modalities. These were subsequently published as separate parts of Topic Group Report 32. Also, one day meetings and training courses were held throughout this period concerned with quality assurance in diagnostic radiology to promote the field of diagnostic radiology medical physics.

Towards the latter part of the 1970’s a CT Users Group was set up by Roy Parker, Chairman of the Scientific Committee of the HPA to develop a test protocol for CT. Roy was a pioneer in the application of CT applied to radiotherapy treatment planning at the Royal Marsden Hospital and gave the first Mayneord Lecture of the British Institute of Radiology (BIR) in 1984 on this topic. Indeed, Professor Val Mayneord had been Roy’s PhD supervisor. The Diagnostic Radiology Topic Group collaborated in this initiative and the programme of work was encouraged by the DHSS. To this end a project was established in 1979 in the North West Regional Department of Medical Physics to design, manufacture and test suitable CT phantoms. The final design was of modular construction with individual segments positioned within a cylinder of 17.5 cms for the head section and 30 cm for the body.

Modules were produced that could assess the following physical parameters:

  • Image noise
  • Uniformity
  • Artefact induction
  • Structural noise
  • Pixel size
  • Spatial resolution
  • Slice width
  • Radiation dose
  • Linearity of CT scale
  • Accuracy of patient positioning devices

An original budget of £400 was allocated to this task, but this was increased to £470 to accommodate an increase in the cost of the materials subsequently required. However, following a visit by Drs White and Speller from St Bartholomew’s Hospital, on behalf of EMI, in January 1980 to test the EMI 7070 at the Christie Hospital, under both head and body modes, a further cost increase was required. One of the tests they performed was a simple and elegant method of determining the tube potential using the attenuation coefficients of various chemical solutions. The method had been described in the January 1980 edition of the British Journal of Radiology.

Since it would not be possible to routinely use an Ardran-Crookes penetrameter to determine the tube kV, this new approach was incorporated into the phantom design. This increased the cost by roughly £93.  However, since a Regional Medical Physics service was envisaged a further £120 was included for a suitable suitcase to transport the phantoms from site to site. The overall cost of materials was eventually, therefore, £692.

In 1980 there were six CT scanners in the North West Region. Their locations were:


Preston Royal Infirmary EMI CT1007 Head Scanner
North West Manchester General EMI CT1010S Head Scanner
Salford Royal Infirmary EMI CT1010S Head Scanner
Manchester Royal Infirmary EMI CT1010S Head Scanner
Manchester University EMI 5005 Whole Body
Christie Hospital EMI7070 Whole Body


Starting in the Spring of 1980 tests were undertaken on these scanners. Tests included both radiation protection measurements of scattered dose around the scanner room during a scan. These measurements were supported by measurements of patient dose at various positions in a CT slice using a phantom for both single and contiguous slices. Also, scattered radiation to critical organs during actual patient scans were assessed. In conjunction with the radiation protection measurements, the physical performance (quality assurance) measurements outlined previously were also performed.

The measurements could be used to compare the performance of different scanners, particularly as new models became available to the market. Thus, in late 1981 a “Which” report on different manufacturers’ scanners was produced in the North West Region as an aid to prospective purchasers of CT scanners. Incidentally, some manufacturers of CT scanners at that time were already disappearing from the field or were taken over by competitors due to fierce competition in the marketplace and/or development of new technology. Consequently, by May 1980 even EMI – Medical had been taken over by IGE.

Through the application of the quality assurance procedures, it was possible to assess the consistency of performance of CT scanners over time or following a service. The test protocol was published by the Hospital Physicist’s Association in 1981 as Topic Group Report 32; “Measurements of the performance characteristics of diagnostic systems in medicine Part 111, The physical specification of computed tomography scanners, associated measurements and their use”. Thus, within a decade of the initial development of CT technology, medical physicists had established standard test procedures for this revolutionary X-ray imaging technique. This initiative demonstrated the value of applied research and development programmes within the field of medical physics in order to help support and develop routine service commitments.

By this time the CT Users Group had turned their attention to the evaluation of the performance of early treatment planning systems that employed CT imaging data in conjunction with software programmes that ran on local minicomputers. In the early 1980’s treatment plans were still being produced manually using radiographic (plain film) images. This is another aspect of medical imaging that has continued to undergo significant technological development.


Dr Mike Moores, Director

April 2022