50 years ago, the first CT scan let doctors see inside a living skull – thanks to an eccentric engineer at the Beatles' record company

X-rays beam through each ‘slice’ of brain, oriented at each degree from 1 to 180 in a semicircle. Edmund S. Higgins, CC BY-ND^[7]

First, he would conceptually divide the brain into consecutive slices^[8] – like a loaf of bread. Then he planned to beam a series of X-rays through each layer, repeating this for each degree of a half-circle. The strength of each beam would be captured on the opposite side of the brain – with stronger beams indicating they’d traveled through less dense material.

Calculating the strength of each X-ray once it’s passed through the object, and working backward with an impressive algorithm, it is possible to construct an image. Edmund S. Higgins, CC BY-ND^[9]

Finally, in possibly his most ingenious invention, Hounsfield created an algorithm to reconstruct an image of the brain based on all these layers. By working backward and using one of the era’s fastest new computers, he could calculate the value for each little box of each brain layer. Eureka!

But there was a problem: EMI wasn’t involved in the medical market and had no desire to jump in. The company allowed Hounsfield to work on his product, but with scant funding. He was forced to scrounge through the scrap bin of the research facilities and cobbled together a primitive scanning machine - small enough to rest atop a dining table.

Even with successful scans of inanimate objects^[10] and, later, kosher cow brains^[11], the powers that be at EMI remained underwhelmed. Hounsfield needed to find outside funding if he wanted to proceed with a human scanner.

Schematic diagram of the CT scanner included in Hounsfield’s U.S. patent. Godfrey Newbold Hounsfield^[12]

Hounsfield was a brilliant, intuitive inventor, but not an effective communicator. Luckily he had a sympathetic boss, Bill Ingram, who saw the value in Hounsfield’s proposal and struggled with EMI to keep the project afloat.

He knew there were no grants they could obtain quickly, but reasoned the U.K. Department of Health and Social Security could purchase equipment for hospitals. Miraculously, Ingram sold them four scanners before they were even built. So, Hounsfield organized a team, and they raced to build a safe and effective human scanner.

Meanwhile, Hounsfield needed patients to try out his machine on. He found a somewhat reluctant neurologist who agreed to help. The team installed a full-sized scanner at the Atkinson Morley Hospital in London^[13], and on Oct. 1, 1971, they scanned their first patient: a middle-aged woman who showed signs of a brain tumor.

It was not a fast process^[14] – 30 minutes for the scan, a drive across town with the magnetic tapes, 2.5 hours processing the data on an EMI mainframe computer and capturing the image with a Polaroid camera before racing back to the hospital.

The first clinical CT scan, with brain tumor visible as darker blob. 'Medical Imaging Systems: An Introductory Guide,' Maier A, Steidl S, Christlein V, et al., editors., CC BY^[15][16]

And there it was – in her left frontal lobe – a cystic mass about the size of a plum. With that, every other method of imaging the brain was obsolete.

Millions of CT scans every year

EMI, with no experience in the medical market, suddenly held a monopoly for a machine in high demand. It jumped into production and was initially very successful at selling the scanners. But within five years, bigger, more experienced companies with more research capacity such as GE and Siemens were producing better scanners and gobbling up sales. EMI eventually exited the medical market – and became a case study^[17] in why it can be better to partner with one of the big guys instead of trying to go it alone.

King Carl Gustaf awards the Nobel Prize to Hounsfield in Stockholm on Dec. 11, 1979. Keystone/Hulton Archive via Getty Images^[18]

Hounsfield’s innovation transformed medicine. He shared the Nobel Prize^[19] for Physiology or Medicine in 1979 and was knighted by the Queen in 1981. He continued to putter around with inventions until his final days in 2004, when he died at 84.

In 1973, American Robert Ledley^[20] developed a whole-body scanner^[21] that could image other organs, blood vessels and, of course, bones. Modern scanners are faster, provide better resolution, and most important, do it with less radiation exposure. There are even mobile scanners.

Modern CT scans provide much higher resolution images of the ‘slices’ of the brain than Hounsfield’s original scan did in 1971.

By 2020, technicians were performing more than 80 million scans annually in the U.S.^[22]. Some physicians argue that number is excessive and maybe a third are unnecessary. While that may be true, the CT scan has benefited the health^[23] of many patients around the world, helping identify tumors and determine if surgery is needed. They’re particularly useful for a quick search for internal injuries after accidents in the ER.

And remember Hounsfield’s idea about the pyramids? In 1970 scientists placed cosmic ray detectors^[24] in the lowest chamber in the Pyramid of Khafre. They concluded that no hidden chamber was present within the pyramid^[25]. In 2017, another team placed cosmic ray detectors in the Great Pyramid of Giza and found a hidden, but inaccessible, chamber^[26]. It’s unlikely it will be explored anytime soon.

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