X-rays are a type of radiation called electromagnetic waves. X-ray imaging creates pictures of the inside of your body. The images show the parts of your body in different shades of black and white. This is because different tissues absorb different amounts of radiation. Calcium in bones absorbs x-rays the most, so bones look white. Fat and other soft tissues absorb less and look gray. Air absorbs the least, so lungs look black.
The most familiar use of x-rays is checking for fractures (broken bones), but x-rays are also used in other ways. For example, chest x-rays can spot pneumonia. Mammograms use x-rays to look for breast cancer.
When you have an x-ray, you may wear a lead apron to protect certain parts of your body. The amount of radiation you get from an x-ray is small. For example, a chest x-ray gives out a radiation dose similar to the amount of radiation you're naturally exposed to from the environment over 10 days.

Fast facts on ultrasound scans

• Ultrasound scans are safe and widely used.
• They are often used to check the progress of a pregnancy.
• They are used for diagnosis or treatment.
• No special preparation is normally necessary before an ultrasound scan.

The person who performs an ultrasound scan is called a sonographer, but the images are interpreted by radiologists, cardiologists, or other specialists.
The sonographer usually holds a transducer, a hand-held device, like a wand, which is placed on the patient’s skin.
Ultrasound is sound that travels through soft tissue and fluids, but it bounces back, or echoes, off denser surfaces. This is how it creates an image.
The term “ultrasound” refers to sound with a frequency that humans cannot hear.
For diagnostic uses, the ultrasound is usually between 2 and 18 megahertzTrusted Source (MHz).
Higher frequencies provide better quality images but are more readily absorbed by the skin and other tissue, so they cannot penetrate as deeply as lower frequencies.
Lower frequencies penetrate deeper, but the image quality is inferior.

How does it capture an image?

Ultrasound will travel through blood in the heart chamber, for example, but if it hits a heart valve, it will echo, or bounce back.
It will travel straight through the gallbladder if there are no gallstones, but if there are stones, it will bounce back from them.
The denser the object the ultrasound hits, the more of the ultrasound bounces back.
This bouncing back, or echo, gives the ultrasound image its features. Varying shades of gray reflect different densities.