What’s the Difference between an X-ray, Ultrasound, MRI and CT Medical Imaging?

Originally posted on April 27, 2019

If you are like most people, you have undergone some type of medical imaging in your life already, such as an x-ray, ultrasound, MRI, or CT. Medical imaging creates pictures of tissues, bones, and organs inside the human body. These imaging technologies help doctors diagnose and assess diseases.

All of these tests are non-invasive, which means they do not involve general anesthesia or stitches. Some types of tests do include the use of an intravenous (IV) needle. These imaging tests are pain-free and provide a wealth of information.

But what exactly are the differences between these medical imaging techniques?

X-rays

X-rays use electromagnetic radiation to create images. During an x-ray, radiation passes through the body onto an x-ray film. Radiation passes right through fluid and thin tissues to cause a dark area on the x-ray film. Bones and other dense tissues stop the x-rays from passing, so these areas show up as light areas on the x-ray film. 

X-rays usually entail standing, or lying, between two pieces of equipment – one piece of equipment sends the radiation out and another contains the x-ray film.

In our clinics, we use digital x-rays.  They work the same way as traditional x-rays but the differences between traditional x-ray machines and our digital ones are: 

  • Uses digital sensors instead of film
  • 80% less ionizing radiation
  • Scans can be enhanced after processing

Health care professionals use x-rays to diagnose bone disease, fractures, dislocations, infections, and tumors.

Ultrasound

Diagnostic medical ultrasounds us a non-invasive diagnostic technique used to image the inside of the body. 

Ultrasounds use high-frequency sound waves to create images. Like x-rays, the ultrasound beams pass through fluid and less-dense tissue. The sound waves bounce off bones and denser tissues. The ultrasound machine uses the echo of the sound waves to create the image. Health care professionals use ultrasound to diagnose problems affecting soft tissues, such as muscles, blood vessels, the heart, and other organs.

To perform an ultrasound, the technician places a handheld wand against your skin. The wand, known as a transducer, emits the sound waves and detects their echoes. A computer converts information from the echoes to create an image.

During an ultrasound exam, your medical professional will apply a gel to your skin. This will prevent air pockets from forming between the transducer and the skin. Air pockets can block ultrasound waves from passing into the body. 

MRI

Magnetic resonance imaging (MRI) uses a strong magnetic field and radio waves to create images of the body that cannot be seen as well with x-rays, ultrasounds, or CT scans. MRIs use powerful magnets to create images.

The human body is made mostly of water, which has a magnetic polarity. In other words, fluid in the body contains atoms that spin at a certain rate. Atoms in some tissues spin faster than atoms in other tissues. In some cases, the atoms in diseased tissue spin at a different rate than in healthy tissue. MRIs use magnets to spin the atoms and radio waves that detect how fast the atoms spin. A computer transforms the information into detailed images.

Health care professionals use MRI to assess joints, muscles, cartilage, ligaments, and tendons. This makes MRIs helpful for diagnosing sports injuries. MRI is also helpful for diagnosing strokes, tumors, aneurysms, multiple sclerosis, spinal cord injuries, and inner ear or eye problems.

An MRI machine is similar to a CT scan in that it involves a large box-like device with a hole in the center. MRIs tend to be very loud and may require special ear protection.

CT

Computed tomography (CT or CAT scan) combines x-rays and a computer to create 360-degree pictures of the spine and of internal organs. During a CT, the technician takes a series of x-ray images from different angles. Then the computer processes and assembles the series of images to create cross-sectional images, or slices, of the bones, blood vessels, and soft tissues. CTs create images that are more detailed than traditional x-rays.

A CT is a large box-like machine with a hole or tunnel in the center. You lie on a table, which passes through the hole during the test.

Dense structures within the body, such as bones, easily show up in the image. However, soft tissue may be difficult to see in the scan.  To help medical professionals identify issues with the soft tissues a special dye, known as contrast, is sometimes administered through an IV.  

For more information on diagnostic imaging, and the differences between the various tests, consult with your health care professional. The more you know about diagnostic imaging, the more control you have over your own health.

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