How This Record Company Engineer Invented the CT Scanner

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.

Hounsfield worked at Electrical and Musical Industry in Hayes, England. Best known for producing and selling Beatles records, EMI also developed electronic equipment.

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 1951 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 warned him that his job would be in jeopardy if he didn't come up with another good idea.

Hounsfield 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 Care.

A CT scanner for cow brains and human ones

Hounsfield worked with neuroradiologists James Ambrose and Louis Kreel to build the first prototype. It was small enough to sit atop a table. They tested the machine on small pigs, and after successfully producing images of their brains, the three men 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 in The 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 physicist Allan MacLeod Cormack's algebraic reconstruction technique. 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. Cormack shared the 1979 Nobel Prize with Hounsfield.

The scan took 30 minutes and the computerized construction of the image took another two hours. The image 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. 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.

Administered by the IEEE History Center and supported by donors, the Milestone program recognizes outstanding technical developments around the world.

The CT scanner's Milestone plaque, which is displayed on an exterior wall at the Old Vinyl Factory, 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.