The inspiration for computed tomography (CT) came from a chance conversation that research engineer Godfrey Hounsfield had with a doctor while on vacation in the 1960s. The physician complained that X-ray images of the brain were too grainy and only two-dimensional.
When Hounsfield returned to work after that vacation, he proposed a project to his supervisor to develop a machine that could create three-dimensional brain images. The machine would project narrow beams of X-rays through a person’s head, and a computer would use the resulting data to construct a series of cross-sections that together would represent the brain in 3D.
Hounsfield worked with neuroradiologists to build the machine, and in 1971 they produced the first computed tomography scan of a human brain. CT scans are now used to pinpoint the location of blood clots, tumors, and bone fractures.
For his invention, Hounsfield was named corecipient of the 1979 Nobel Prize in Physiology or Medicine.
Hounsfield’s scanner was commemorated with an IEEE Milestone during a ceremony held on 26 October at the EMI Old Vinyl Factory, in Hayes, England, where the technology was developed. The IEEE United Kingdom and Ireland Section sponsored the nomination.
Selling Beatles albums and developing medical equipment
After the X-ray machine was invented in 1896, it quickly became standard equipment in hospitals. The machines produce great images of bones because their dense structures absorb X-ray beams well. The absorption pattern makes the bones look white on film. But soft-tissue organs such as the brain looked foggy because the radiation passed through them.
While Hounsfield served with the Royal Air Force, he learned the basics of electronics and radar. In 1949 he joined EMI, where he developed guided weapon systems and radar. His interest in computers grew, and in 1958 he helped design the Emidec 1100—the first commercially available all-transistor computer made in Britain.
After that project, Hounsfield’s supervisor gave him the opportunity to come up with his own research idea.
Hounsfield decided to pursue pattern recognition and thought back to the conversation with the doctor about the limitations of X-ray images, then he proposed the project that would become the CT scanner.
EMI didn’t develop or manufacture medical equipment and wasn’t interested in getting into that line of business, but Hounsfield’s supervisor believed in his idea and approved it. The company couldn’t fully fund the project, so Hounsfield applied for and received a grant of around US $40,000—approximately $300,000 in 2022 figures—from the British Department of Health and Social Security.
A CT scanner for cow brains and human ones
Hounsfield worked with radiologists James Ambrose and Louis Kreel to build the first prototype. It was small enough to sit atop a table. Ambrose and Kreel provided Hounsfield with small pigs and human vertebrae to test the machine on. After successfully producing images, Hounsfield built a full-size scanner.
The CT scanner was first tested on human brains preserved in formalin. But the brains weren’t ideal because the chemical had hardened their tissues so severely that they no longer resembled normal brain matter, as described in an article about the scanner inThe Jewish News of Northern California. Because the scanner was intended for use on living patients, Hounsfield and his team looked for a brain similar to a human’s.
They procured fresh cow brains, but those couldn’t be used because an electric shock was used to stun the animals before they were slaughtered. The procedure caused the brain to fill with blood, and the fluid obstructed the radiologists’ view of the organ’s structure.
Ambrose, who was part Jewish, suggested using kosher cow brains because instead of being stunned, the animals had their jugular slit. The process drained blood away from the skull—which enabled clear CT scans of the brain.
After several successful tests, the machine was ready to be tried on a human. The scanner was installed in 1971 at Atkinson Morley Hospital, in London, where Ambrose worked. The first patient was a woman who showed signs of a brain tumor.
She lay on a table as X-rays were shot through her skull from a single site above her head. The beams passed through her and struck a crystal detector housed in the gantry below her head. Both the X-ray source and the detector moved around her in 1-degree increments until they had turned 180 degrees, with each device ending up at the other one’s starting point.
That allowed the scanner to depict the brain in individual layers. Hounsfield described it as putting the brain “through a bacon slicer,” according to an article about the scanner on the Siemens MedMuseum website.
The detector recorded the X-ray signals and sent the data to a computer. The computer constructed an image of the brain using an iterative reconstruction technique Hounsfield created. The technique built up an image by filling in a matrix, each square of which corresponded to a part of the examined organ, according to a Nobel news release about the scanner. Because the crystal detector was 100 times more sensitive than X-ray film, the density resolution was much higher, making the resulting image much clearer. Physicist Allan MacLeod Cormack had experimented with his own reconstruction method from 1963 to 1964, discovering that obtaining images of the body’s interior was possible. Cormack shared the 1979 Nobel Prize with Hounsfield.
The 5-minute scan took two 13-mm thick image slices, which showed a cystic mass about the size of a plum on the patient’s left frontal lobe.
EMI began manufacturing CT scanners and sold them to hospitals with success. The machine had a mini-computer attached to it, which allowed doctors to scan 14 patients in an eight hour day. Each patient had six to eight image slices taken of their brain. But within five years, General Electric, Siemens, and other companies began making more enhanced, full-body scanners. EMI eventually stopped producing its scanners because it couldn’t compete with the other manufacturers.
The CT scanner’s Milestone plaque, which is displayed on an exterior wall at Jupiter House, the former EMI head office in Hayes, England, reads:
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.
This article appears in the September 2023 print issue as “The CT Scanner Was Invented by a Music Company Engineer.”
This article has been updated from an earlier version.
- The Women Behind ENIAC ›
- Path Found to a Combined MRI and CT Scanner ›
- The Superconducting Shields Behind MRIs’ Triumph ›
- How the Computer Graphics Industry Got Started at the University of Utah - IEEE Spectrum ›