A Gentleman´s Crazy IdeaThe history of computed tomography

In London, in fall 1971, a radiologist and an engineer found themselves jumping up and down for joy – as one of them later recalled – “like football players who had just scored a winning goal.” In their hands, the two researchers were holding a completely new type of X-ray image – known as a tomogram – that depicted a human brain in unprecedented quality. Indeed, looking at the image, the radiologist, James Ambrose, could see his 41-year-old patient’s brain “in a great deal more detail than we’d expected” and could clearly make out the cortex, the spaces filled with cerebrospinal fluid, and even the white matter. The engineer, Godfrey Hounsfield, had developed the new X-ray technology almost single-handedly. With the prototype of his “3D X-ray machine,” Hounsfield ushered in the development of what has become one of the most important techniques in medical imaging: computed tomography (CT).

Godfrey Hounsfield’s prototype was based on what one superior (positively) described as a “crazy idea”: Hounsfield wanted to depict the inside of objects in individual layers, “like putting the object through a bacon slicer.” After several months of persuasion, he received a budget from his employer, the electronics and record company EMI, to build a prototype.  

The first clinical model, which was tested at James Ambrose’s department at Atkinson Morley Hospital in Wimbledon from October 1, 1971, did not include a computer to generate the image – nor were there initially any plans to incorporate one into future CT scanners. The data collected from the brain was stored on a magnetic tape and taken by car to an EMI lab about 20 kilometers away. When Hounsfield and Ambrose published the first test results on April 20, 1972, they triggered the greatest sensation in medical X-ray technology since the discovery of X-rays. Practically from one day to the next, computed tomography set a new course for the development of medical X-ray technology.

The history of computed tomography at Siemens Healthineers began with a trip to EMI’s research laboratory in London in 1972. According to Friedrich Gudden, the head of Siemens X-ray development at the time, the visit was highly informative: “Excellent food and Godfrey Hounsfield, the inventor of computed tomography, joined in. He made an excellent impression on me, calm and unpretentious, a real British gentleman. And what he explained was fascinating – for example, that collecting the measurements for an image took nine days at the start.”

The same year, the fundamental research unit at Siemens in Erlangen began developing a powerful CT scanner that was optimized for workflows in hospitals and medical practices. Some 30 years later, Friedrich Gudden described the “tremendous enthusiasm” with which the Siemens team applied themselves to their work as being “unforgettable.” Work continued every day until late into the night, and Gudden often drove employees who relied on public transit home personally after midnight.  

When Siemens tested the SIRETOM prototype at Goethe University Medical Center in Frankfurt from mid-1974 onward, “legions of visitors were brought to Frankfurt, including competitors, who admired the processing time, convenient use, and image reproduction alike.” Gudden also pointed out that SIRETOM was far superior to all other units on the market in those days. “If we had been able to deliver at the time, any number of them would have been sold. When American doctors asked about the delivery time and heard our answer, they either laughed or cried, depending on their nature.”

One year later, in November 1975, SIRETOM entered series production – and the engineers at Siemens Healthineers would go on to shape the development of computed tomography over the following 45 years with a string of groundbreaking inventions. Modern CT scanners still operate according to the basic principle thought up by Godfrey Hounsfield – but they are worlds apart from the early devices in terms of technology. The major milestones from Siemens Healthineers, such as Spiral CT, PET/CT, and Dual Source CT, will certainly not be the last developments in the history of computed tomography – for as Godfrey Hounsfield once remarked: “Many discoveries are probably lurking around the corner, just waiting for someone to bring them to life.”