Imagine if you told a time-traveler from medieval times that you had a machine that could look at the bones inside your body. They would probably assume you meant either witchcraft or some kind of gruesome skinning process. Luckily for us, x-ray photography works without either. Your bones, muscles, organs, and skin just have different densities. When you get an x-ray at the hospital, the less dense skin, muscle, and other soft tissues look transparent, but the bones inside are brightly visible.
Fig.1 Medical x-rays allow us to see our bones without removing all the annoying skin and flesh in the way. Isn’t science great? (Image via Wikipedia)
Not only are x-rays a crucial tool for diagnosing and treating injuries, they can be used to see inside all kinds of living things (not just humans who accidentally hit their hand with a hammer trying to assemble Ikea bookshelves). Using x-ray techniques in research really does feel like a superpower—if you think something looks cool on the outside, just wait until you see how complex and beautiful it is on the inside!
In my research, I use the same general principals of x-ray photography, but turned up to 11. If you’ve ever had a hospital CT scan or watched an episode of a medical TV show, you know there are ways to visualize the entire human body in slice-by-slice cross-sections. CT (or “computed tomography”) scanning involves taking dozens to hundreds of x-ray snapshots at angles all around the object or person. A computer algorithm puts together all these snapshots into 360-degree array of x-ray images and then slices the object in a cross-sectional view.
Fig. 2 A CT scan uses x-ray images from many different angles to obtain inside-out information from an object in 3D. In some cases, the object rotates on a stage in front of the x-ray source, but in hospital CT machines, the x-ray source rotates around the person being scanned. (Image via MicroPhotonics)
We can use big CT scanners to image humans and look for internal injuries or tumors, or we can use extremely high resolution versions of these machines called micro- or nano-CT scanners to look at tiny structures in small objects—like the arrangement of delicate nerves in small animals or the microscopic structure of tooth enamel .
Fig. 3 In order to diagnose brain injuries or cancer, medical CT scans take many x-ray “slices” through a person’s head. At the top left of this figure the slices start near the chin, and move up towards the top of the head on the bottom right. A contrast agent has been used so the soft brain tissue is visible in addition to the hard bone. (Image via Wikipedia)
CT scanning lets us visualize internal details of specimens without having to cut them up or otherwise destroy them. It really is like x-ray vision! We can also use the CT scan slices to build 3D models that can be used to answer questions about the size, shape, and development of anatomy in different animals. Scientists have used CT scanning to virtually “open up” and look inside alligator jaws, fish from all around the world, tiny ants, and so many more—no scissors or black magic required.
Fig 4. We can start with an animal like the adorable fringe-lipped bat (top left), and use a microCT scanner to obtain many detailed x-ray projection images all around the specimen (top right). The computer then combines these x-rays and slices them into a stack of 2D images, showing the outlines of the bones and teeth (bottom right). When we put all those slices together, we can create a super detailed 3D model of the bat skull for further study—all without having to cut up or destroy a valuable museum specimen just to learn more about it. (Image by Abby Vander Linden).
If I ever get bitten by a radioactive spider, I sincerely hope I’ll get x-ray vision superpowers for real. Until then, using a microCT scanner is a pretty great way to get acquainted with the beautiful insides of objects all around us.
- Holdsworth, D. W. and Thornton, M.M. “Micro-CT in small animal and specimen imaging.” Trends in Biotechnology 20 (2002): S34-S39
More From Thats Life [Science]