You may not have had a CT scan yourself, but the chances are that a close friend or relative has had one. What is commonplace and routine today was unheard of until 1971, when the first CT head scanner became operational, or 1975 for the CT whole-body scanner.
X-rays were first used in medicine long before that, in Birmingham, England, in 1896, the year after their discovery by Röntgen, and had proved their value in many fields. Although they are good at showing radio-dense structures like bone, soft tissues in important organs like the heart, gut, and brain do not show up on conventional X-rays.
One way of working round this is to put a radio-dense substance (usually based on iodine) into the organ, by injecting it into the circulation, or in the case of the brain, by putting it into the fluid cavities within the brain, the ventricles. Even so, X-rays remain very limited in what they can show.
Another problem with conventional X-rays is that they do not show a cross-section through the body, but sandwich everything into a single plane. If someone had an air-gun pellet inside their head, which showed up on X-ray, you would have to take a minimum of two X-rays to see where it was. During the twentieth century, this was partially addressed using a technique called tomography, but the results were seldom that good, and still only worked for suitably radio-dense objects.
The maths involved in CT scanning was developed back in 1917 by the Austrian Johann Radon, but it was not until the advent of reasonably powerful computers that this could be implemented in working form – something accomplished by Sir Godfrey Hounsfield between 1967 and 1971. His first CT scanner, which worked on the head only, was installed at the Atkinson Morley Hospital in Wimbledon, England, and scanned its first patient on 1 October 1971.
By modern standards, this was an amazingly crude and slow machine. The patient had to lie down, motionless, their head enveloped in a large rubberised waterbag, for just over five minutes, during which the X-ray beam and detector chugged around making 180 measurements for every ‘slice’ that made up the whole scan. Each set of images then took well over two hours to process in the computer (which was as large as the scanner!), before they were printed out on a large photographic film.
Hounsfield was working for EMI, and it is often claimed that profits from the sales of Beatles and other popular records in the previous decade had been used to fund this R&D. However once EMI was able to offer production scanners, priced at over £1 million each, I am sure that its investment was quickly repaid.
US researchers had also been following similar leads: Allan M Cormack at Tufts University, MA, independently invented a CT scanner; Robert S Ledley at Georgetown University improved the design to eliminate the waterbag, increase the resolution, and operate much faster. The latter was known as the ACTA scanner, and used a DEC PDP11/34 minicomputer to control the scanner and perform the calculations. It must have made a lot of money for Pfizer, who purchased the rights to the design.
I first used a CT scanner back in the autumn of 1979, when I was a junior doctor (houseman, or intern) in neurosurgery in Cardiff, which had the first CT head scanner in Wales. I believe that was an EMI model, which took around 4 minutes to perform the scanning, and still had a waterbag.
It was at the leading edge of medical technology, and a huge step forward for us, turning what had been very tricky diagnoses into more straightforward matters of interpreting the scan correctly. For the neurosurgeons, who were preparing to open up someone’s skull and rummage around looking for a tumour, it gave vital information which was saving lives daily. For many patients with head injuries, it usually delivered a diagnosis before taking them to surgery, which was truly revolutionary.
By about 1980, leading hospitals were starting to add CT whole-body scanners to their X-ray departments, and they have brought about similar revolutions in the diagnosis of many conditions affecting the rest of the body.
When I worked in the Field Hospital on the Falkland Islands during the conflict there in 1982, CT scanners were still too large and complex to use in such combat settings. By the time of the military operations in Afghanistan over the last decade, smaller and more portable units were considered to be essential to any modern field hospital, and helped save many lives and limbs.
Other types of scanners appeared later, notably MRI (magnetic resonance imaging) from 1980 onwards; they do not use X-rays, but very powerful magnets which affect water molecules in tissues in particular. CT remains more popular than MRI scanning, but the techniques are complementary rather than competing.
The Visible Human Project, at the US National Library of Medicine, has brought together CT, MRI and microscopic analysis to present the ultimately detailed account of the anatomy of the entire human body. Some sample images are freely available; a licensing agreement is required for access to the complete data.
CT scanning is now quite widely used outside medicine. Some startling images have been made of archaeological specimens such as mummies, and it has even been used on violins. Much faster and more sophisticated computing can also be used to assemble the ‘slices’ from a scan into a realistic 3D model.
To the best of my knowledge, CT scanners were the first area in medicine which were entirely dependent on medical computing. As Apple and others take iPads, iPhones and now the Watch into new and exciting fields of medicine, it is worth remembering the pioneering work of Radon, Hounsfield, Cormack, Ledley, and others, whose technologies we have come to take for granted.