|An MRI scan of the brain|
Although physicians are likely familiar with the history of medical imaging, a brief summary is provided below to show how far the field has come.
The first X-ray was taken of the hand almost 120 years ago, on December 22, 1895 by a German physicist (Wilhelm Rontgen). Rontgen did not know what type of rays he was dealing with, which is why he referring to them with the letter “x” (to designate an unknown quality). He discovered the rays when noticing a light green glow that looked like the bones of his hand on a fluorescent screen. The screen was about three feet away from an energy discharge tube he was experimenting with that was covered in black cardboard to prevent light from escaping. He reasoned that the glow was caused by invisible energy that even passed through items on his desk. He took the x-ray picture of his wife’s hand bones soon thereafter and medical imaging was born.
X-rays became a useful way to quickly image the bones and became widely used by physicians at the time to improve diagnosis (e.g., bone fractures, dental cavities) and treatment. Although many people associate x-rays with images of bones, they are also able to provide images of other bodily structures such as the lungs. This is why they are often used to help diagnose pneumonia. A downside of x-rays is radiation exposure, which has long-term health risks that increase with the amount of radiation exposure. These effects became more well-known in the early 1900s. Medical ultrasound imaging, which produces images of body parts from the reverberation of sound waves, does not involve any radiation and has been used for the last 50 years or so. This is why ultrasounds are used instead of x-rays to obtain images of the fetus during pregnancy.
Although ultrasound is not considered harmful, the images produced are of low resolution and quality. The same is true for x-rays. To correctly assess and diagnosis conditions that require higher imaging quality, more advanced techniques were created such as CT (computerized tomography) scans and MRI (magnetic resonance imaging) scans. CT scans, which were first used in 1971, uses a combination of x-rays, cameras that scan the entire body while rotating around the patient, and computer technology to provide high quality 3D images.
While the image quality of the CT scan is much better compared to the x-ray, CT scans use much more radiation (e.g., hundreds of times more) than a traditional x-ray. MRI scans (first used on humans in 1977) get around this problem by providing even higher quality 3D images without the use of radiation. Instead, MRIs use high powered magnets to exploit the magnetic properties of cells in the body. The result is an image that is a very close replica of the body part being imaged. The downside to MRIs compared to CT scans is that they take much longer, are more expensive, are not as good at visualizing internal bleeding, and cannot be used in patients with certain types of metallic implants. This is why CT scans tend to be used over MRIs in emergency rooms because the physician needs to quickly determine if there is evidence of internal bleeding that requires emergency intervention. In non-emergency situations, however, the MRI tends to be used.
Medical imaging continues to make dramatic advancements and as a result of the above technologies, there are many specialized imaging techniques used throughout the various medical specialties. It will certainly be interesting to see what the next 120 years brings!