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Wednesday, December 07, 2022

For 50 years, CT scans have saved lives, revealed beauty and more

One grainy, gray-scale image of a brain has changed science and medicine forever.

Half a century ago, the first CT image of a patient lifted the veil of invisibility that covers the inside of the human body, giving scientists a window inside us, unlike before.

Today, physicians in the United States alone order more than 80 million scans per year. X-ray computed tomography, or CT, is often the fastest way to get a grip on what is causing a mysterious woe. CT scans can eradicate heart disease, tumors, blood clots, fractures, internal bleeding and more. The technique can give surgeons knowledge of what they will encounter in a patient, and lead treatment for cancer and other diseases.

“It answers so many questions quickly. That’s why it’s used, ”says medical physicist Cynthia McCollough of the Mayo Clinic in Rochester, Minn.

A CT scan involves thousands of X-ray measurements taken from various angles. This is how it works: A source of X-rays revolves around the body and sends a beam of radiation through bone, blood and tissue, while rotating detectors measure the beam it passes through.

Different materials in the body absorb X-rays differently. The calcium in bone, for example, absorbs X-rays powerfully, while soft tissue absorbs less. So when the data collected by the detectors is stitched together by a computer, it can form a cross-sectional view of what is inside, based on where X-rays are more or less absorbed. By sliding the table holding the patient so that the X-ray and detectors slide along the body, it enables 3D reconstructions of organs and other parts.

Over the years, scientists have continually improved the technology, making it faster and higher resolution and reducing the amount of radiation patients receive. These improved CT scans painted more and more detailed landscapes of the human body. It’s hard not to marvel at the beauty of the interior that brings the scans to the surface.

Here’s a look back at some of the great advances in CT scans over the last 50 years.

The CT scan is born

In 1971, radiologist James Ambrose at Atkinson Morley Hospital in London performed the first CT scan of a patient in collaboration with engineer Godfrey Hounsfield, the technology’s inventor. Hounsfield worked for the British electronics company EMI, best known for his role as the record company for the Beatles.

First Ct Image Of A Patient Showing The Brain Area
In 1971, the first CT scan of a patient (shown) exposed the brain and revealed a tumor (dark circle at top left).A. Maier et al/Medical Imaging Systems: An Introductory Guide 2018 (CC BY-ND 4.0)

The scan, an image only 80 pixels by and 80 pixels wide, did not provide much detail. But it showed the technology’s potential and revealed a tumor in a woman’s brain. A surgeon who later operated on the tumor apparently surprised him that “it looks exactly like the picture”.

Previously, when doctors wanted to look for a brain tumor, they injected air into the spine. Then they rotated the patient to cause the air in the area around the brain to bubble up to increase the contrast in standard X-ray images. The procedure “hurt like that,” McCollough says. “Patients vomited frequently; it was like torture. ” With CT scan, that anxiety soon became a thing of the past.

However you cut it

Initially, CT scanners were designed to image only the brain. But researchers have quickly adapted the technology to take cross-sectional images, or slices, at various points along the body. Then, in the early 1990s, scanners were created in which the X-ray source scanned in a continuous spiral around the body, instead of taking individual diameters. That progress allowed an entire organ, such as the lungs, to be imaged at once.

A Black And White 2-D Lung Scan Alongside A Purple 3-D Version
CT scanners with multiple rows of detectors can image multiple cross-sections, or slices, of the body simultaneously, which improves image resolution. These images of lungs with emphysema were taken with a 128-cut scanner, shown in a 2-D image (left) and a colored 3-D reconstruction (right).P. Rogalla, C. Kloeters and PA Hein /Radiological Clinics of North America 2009

But the image resolution along the length of the body was still low. CT scanners with multiple rows of X-ray detectors solved this problem by imaging multiple slices of the body simultaneously along the spiral path.

CT scanner manufacturers have continued to push up the number of detectors, making scanners capable of capturing multiple disks simultaneously. When detectors hit 64 cuts in the early 2000s, McCollough says, “the real ‘Wow’ happened.” Scans can be fast, high resolution and cover a significant length of the body, all at once. Today, scanners are even more sophisticated and use up to 320 slices.

Finally, the fragile complexity hidden in the human body – from the intricate webs of blood vessels to the gracefully branching airways of the lungs to the delicate yet sturdy structure of bone – was there for all to see.

Doubling

When McCollough’s father-in-law ended up in the emergency room with a painful pulse, he fainted for hours while doctors tried to figure out what was wrong. Finally, McCollough recalls, she asked, “Can’t we send him to CT?”

Thanks to a technique called dual-energy CT, doctors were able to diagnose the problem. Launched in 2006, dual-energy CT uses two X-rays at different energies, instead of just one. By taking pictures in this way, the scanners can determine exactly what material is inside. Different materials absorb X-rays in different amounts, but to switch to a specific type of material, you want to know how that absorption changes as the X-rays’ energy changes.

For example, dual-energy CT can distinguish between different types of crystals that can form in the joints, causing arthritis. Urate crystals indicate gout, and crystals containing calcium indicate pseudogout. For McCollough’s father-in-law, the scan quickly discovered the cause of his pain: pseudogout. In this way, CT scans can reveal the human body at its most basic level, the material of which it is composed.

Ct Scan Of A Hand Showing Urate Crystals Around The Wrist And Finger Joints In Green
A dual-energy CT scan shows a clear marker of gout, the presence of urate crystals (shown in green in this false-color 3-D representation) in joints between the bones of the hand (white and purple).MA Desai et al /Radiography 2011

Count on it

The X-ray detectors in CT scanners are the “secret sauce” of the technology, McCollough says, because the detectors are how the machines measure the X-rays in the first place. Most CT scanners measure that radiation indirectly, first converting the X-rays into visible light and then converting that light into an electrical signal. A new era of CT technology cuts out the middleman. In September, the US Food and Drug Administration launched the first “photon-counting” CT scanner.

X-rays are a type of high-energy light, and like all light, they consist of particles called photons. Photo-counting CT scanners measure individual X-ray photons. The technology also allows for sharper, more detailed images and provides a measure of the energy of the photons, which, like dual-energy CT, identifies different materials within the body.

Images Of A Broken Wrist In A Standard Ct Scan And A Photo-Count Ct Scan
Photo-counting CT scans are praised for their high-resolution images. In a conventional CT scan of a broken wrist (left, fracture indicated by an arrow), the structure of the bone is vague compared to a photon counting scan of the wrist (right).Mayo Foundation for Medical Education and Research

Beyond the (human) body

CT scans may have been invented for medicine, but that has not stopped other researchers from recognizing the technology’s usefulness. Scientists in fields including archeology, biology and physics have used the technology to better understand everything about mummified remains (SN: 8 /20/20) to how cracks in concrete form on the anatomy of animals such as the surviving monitor lizard (Lanthanotus borneensis).

Ct Scan Of A Curled Monitor Lizard Showing The Skeleton In White And Bony Armor In Green
Created using CT scan, this colored 3-D reconstruction of an overgrown monitor lizard reveals its skeleton (off-white) and bony armor (green).Edward Stanley / Florida Museum of Natural History / Univ. of Florida

This image of L. borneensis comes from the Florida Museum of Natural History in Gainesville. Researchers there are making 20,000 CT data sets of preserved specimens representing each vertebrate genus housed in American natural history collections to reveal the animals’ internal anatomy. Anyone in the world will be able to access these scans online.

The next 50 years

Despite all these advances, some researchers warn that doctors’ love affair with CT has gone too far, at least in the United States, where the scans are used more often than in many other countries. Unnecessary CT scans can have disadvantages: It can expose unrelated findings that seem worrying but are likely to be benign, which can lead to costly and anxiety-inducing additional tests. But previous CT scans can also have a negative impact, delaying the diagnoses for ailments that resolve best if treated quickly.

Colored Ct Scan Showing Areas Of The Lung Damaged By Covid In Green And Non-Damaged Areas In Blue
In patients with COVID-19, CT scans may reveal damaged parts of the lungs, which are shown in green in this colored image of a cross-section of the chest.Steven Needell / Science Source

There is no denying that, when justified, CT scans are a crucial, life-saving part of the medical toolkit. Recently, the scans were in the spotlight for revealing damage to the lungs by COVID-19 (SN: 27/4/20). Technology seems ready to remain a mainstay of medicine and science in future decades, and will continue to seek its way to our hearts, lungs, brain and everywhere else.

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