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50 years of engineering - 1972: CT scan

20/01/2020
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To celebrate Fircroft’s 50th Anniversary, every Monday EngineeringPro will be highlighting an engineering accomplishment made each year from 1970-2020. This week we’re looking back to 1972 and an invention that transformed modern medicine: the CT (or CAT) scan.

A human brain made visible by CT scan
(Image via Wikimedia Commons)

Originally called the Computed Axial Tomography (CAT) Scan, now simply known as the Computerised Tomography (CT) Scan, this Nobel Prize winning invention is used to produce detailed images of structures such as internal organs, blood vessels and bones for diagnostic and monitoring purposes. 

But it was not initially envisioned for such a purpose, the original idea described simply as “a realisation that you could determine what was in a box by taking readings at all angles through it.”

“Don't worry if you can't pass exams, so long as you feel you have understood the subject.” - Sir Godfrey Hounsfield in his 1979 Nobel Prize acceptance speech
(Image via Wikipedia)

The man responsible for that realisation was Sir Godfrey Hounsfield, an electrical engineer who researched guided weapons systems and radar at EMI Ltd. and helped design the first commercially available all-transistor computer made in Great Britain. On a weekend ramble in 1967 Hounsfield’s mind wandered to the potential for creating detailed images from hundreds of x-ray beams angled around an object contained in a box.

He began working on a device back at the EMI research laboratories that would be able to process such information. Rather than recording x-rays on film, his device would use other sensors that could collect the x-ray data from a rotating photon source - essentially a frame with an x-ray tube on one side and a curved detector on the opposite side.

As x-rays pass through an object they are absorbed at different levels, creating a matrix of x-rays beams of varying strengths which are picked up by the sensor. As the frame rotates, the x-rays pass through the central object at every angle, creating a series of “slices”. Hounsfield’s computerised device would then process the x-ray profiles detected by the sensor to reconstruct a two-dimensional image showing the different tissue densities of the slices.

Hounsfield's initial sketch demonstrating what would later be known as a CAT scan
(Image via Wikipedia)

Hounsfield wasn’t the first to consider how this could work, but other research teams had balked at the incredibly complex mathematics that such a device would require and dismissed the idea as “unworkable”. 

But Hounsfield worked on his device for four years until he had a preliminary system that he used to scan the head of a cow that a colleague obtained from an east London kosher slaughterhouse. When convinced that the system could work (and was safe) he began testing it on his own brain, and in September 1971 scanned the first patient at Atkinson Morley’s Hospital in Wimbledon with the radiologist James Ambrose. From the results Dr Ambrose was able to clearly see the location of a cyst in the patient’s brain. 

The first scans took several hours to acquire the raw data for each slice, and days to reconstruct a single image. Hounsfield continued to develop the device over the next few months and in October 1972 was able to display, to an audience of 2000 at a Chicago-based meeting of the Radiological Society of North America, the first working tomographic scanner, with the ability to produce detailed cross-sections of the brain in four and a half minutes. He received a standing ovation.

Back to the original problem of computing hundreds of x-ray images from a rotating source - there was one other who independently came up with a solution. South African nuclear physicist Allan Cormack published a paper on a potential reconstruction technique in 1957 and so, in 1979, both scientists were jointly awarded the Nobel Prize in Physiology or Medicine.

A modern CT scanner
(Image via Flickr)

Today there are thought to be around 30,000 CT scanners installed worldwide, with the latest systems able to reconstruct a 512 x 512 matrix image from millions of data points in less than a second. In 1976 the first full-body CT scan was introduced and today an entire chest can be scanned in five to ten seconds.

A quantitative measure of radiodensity used to measure the brightness of tomograms to evaluate CT scans is known as the Hounsfield scale.

Artwork depicting Pioneer 10 flying past Jupiter, on route to become the first man made object to leave the solar system
(Image via NASA)

The engineering world of 1972

Other major engineering milestones from 1972 include:

  • Pioneer 10, the first mission to be sent to the outer solar system is launched on 2nd March
  • The first e-mail program is written to send messages across the ARPANET. It is created by Ray Tomlinson, who sent the first test message to himself - including the @ sign in the address.
  • The first home video game system, the Magnavox Odyssey is demoed in May and goes on sale in August. 9,000 units are sold. It is followed - and surpassed - in November by the first generation of Atari’s arcade classic, Pong.
  • The first flight of the Airbus A300 takes place on the 28th October.

Read last week’s look back at 1971 and the launch of the world’s first space station, Salyut 1.

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50 years of engineering - 1972: CT scan - Time to read 5 min
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