Seeing inside the body
Before X-rays, doctors could only guess what was happening inside a patient’s body, or find out through surgery. X-rays let doctors see bones, find broken bones, spot disease and locate swallowed objects, all without cutting the skin.
An accidental discovery
On November 8, 1895, German physicist Wilhelm Röntgen was experimenting with a cathode ray tube in a darkened lab. The tube was covered in black cardboard, yet a nearby screen coated with a special chemical began to glow.
Röntgen realized an invisible kind of ray was passing through the cardboard. Not knowing what it was, he called it an "X-ray," with X meaning unknown.
Soon he discovered the rays passed through paper, wood and flesh but were blocked by bone and metal. One of his first X-ray images showed the bones of his wife Anna Bertha’s hand, along with her wedding ring. Seeing it, she reportedly said, "I have seen my death."
Röntgen won the first Nobel Prize in Physics in 1901. He refused to patent his discovery so everyone could benefit from it.
X-rays spread quickly
| Year | Event |
|---|---|
| 1895 | Röntgen discovers X-rays |
| 1896 | X-rays used to find bullets and examine broken bones within weeks; McGill University physicist John Cox took one of the first medical X-rays in Canada to locate a bullet in a patient’s leg |
| 1896 | Thomas Edison develops an improved fluoroscope |
| 1914–1918 | Marie Curie organizes mobile X-ray units ("Little Curies") to treat soldiers in World War I |
| 1970s | CT scans invented by Godfrey Hounsfield and Allan Cormack (Nobel Prize, 1979) |
| 1990s–today | Digital X-rays replace film |
What are X-rays?
X-rays are part of the electromagnetic spectrum, like light and radio waves, but with very short wavelengths and very high energy.
| Wave | Wavelength | Energy |
|---|---|---|
| Radio waves | Longest | Lowest |
| Visible light | Medium | Medium |
| X-rays | Very short | High |
| Gamma rays | Shortest | Highest |
How an X-ray image is made
- An X-ray machine shoots a beam of X-rays through part of the body.
- Dense materials like bone and metal absorb many X-rays.
- Soft tissues like skin, fat and muscle let most X-rays pass through.
- A detector (or film) on the other side records the X-rays that get through.
| On the image | Shows | Why |
|---|---|---|
| White | Bones, metal, teeth | They block X-rays |
| Grey | Muscles, organs | They block some X-rays |
| Black | Air (lungs) | X-rays pass right through |
The image is called a radiograph. A radiologist is a doctor who specializes in reading these images.
Uses of X-rays
In medicine
| Use | Example |
|---|---|
| Broken bones | Finding fractures |
| Dental X-rays | Finding cavities and checking teeth |
| Chest X-rays | Detecting pneumonia, tuberculosis and lung problems |
| Mammograms | Screening for breast cancer |
| CT scans | Many X-rays from different angles combined by computer into detailed cross-section images |
| Radiation therapy | High-energy X-rays target and destroy cancer cells |
Beyond medicine
| Use | Example |
|---|---|
| Airport security | Scanning luggage |
| Industry | Checking welds and aircraft parts for hidden cracks |
| Art and archaeology | Seeing hidden layers under paintings; examining mummies without unwrapping them |
| Science | X-ray crystallography revealed the structure of DNA |
| Astronomy | X-ray telescopes study black holes and exploding stars |
Safety
X-rays are ionizing radiation: they have enough energy to damage cells and DNA. Early researchers didn’t know this, and many suffered burns and cancer.
Today, X-rays are used safely:
- Doses are kept as low as possible.
- A single chest X-ray gives about the same radiation as a few days of natural background radiation.
- Lead aprons protect other parts of the body.
- X-ray technicians stand behind shields.
- Doctors order X-rays only when the benefits outweigh the small risks.
In the early 1900s, shoe stores used X-ray machines to check shoe fit! They were banned once the dangers were understood.
Common mistakes
- Thinking X-rays make you radioactive. They don’t; the radiation stops when the machine turns off.
- Thinking X-rays show everything. Soft tissues often need other tools like ultrasound or MRI.
- Thinking X-rays are visible. They’re invisible to our eyes.
Try it yourself
- Shine a flashlight through your fingers in a dark room. Light passes through thin tissue but not as easily through bone. How is this similar to an X-ray?
- Look at an X-ray image online. Identify which parts are bone, soft tissue and air.
- Make a chart comparing X-ray, CT, ultrasound and MRI imaging.
Quick recap
- Wilhelm Röntgen discovered X-rays by accident in 1895.
- X-rays are high-energy electromagnetic waves.
- Bones block X-rays and appear white; soft tissue lets them through.
- X-rays are used in medicine, security, industry, art and science.
- X-rays are ionizing, so doses are kept as low as possible.