Basics of X-ray
X-rays are high-energy electromagnetic radiation that can pass through the body. Understanding the basic principles helps you read an X-ray report with more confidence.
How X-rays are produced
X-rays are produced by an X-ray tube. Inside the tube, electrons are accelerated by high voltage and strike a metal target, releasing radiation. The operator sets the voltage (kV) and current (mA) according to the body part being examined.
The beam is directed at the patient. Some rays pass through tissue while others are absorbed. A detector on the opposite side captures the rays that get through and converts them into an image.
Why bone looks white and air looks black
Each tissue absorbs X-rays differently depending on its density. Bone, rich in calcium, absorbs many rays and appears white (radiopaque). Air in the lungs absorbs very few rays and appears black (radiolucent).
These differences in absorption create contrast in the image. Radiologists distinguish structures such as ribs, the heart, and the diaphragm by their shades of grey.
Safety and dose
X-rays are ionizing radiation, so exposure should be kept as low as possible. The dose varies by exam. A chest X-ray is among the lowest, while abdominal or pelvic exams deliver higher doses.
Doctors always weigh the diagnostic benefit against radiation risk. Repeated exams should be discussed with a doctor so they are done only when truly needed.
Key points
- Bone absorbs more X-rays and appears white.
- Air in the lungs appears black because absorption is low.
Educational information, not a substitute for medical advice.