Difference in X-ray, CT, MRI, Ultrasound

X-ray, CT, MRI and ultrasound are the most common imaging examinations nowadays. However, what can each of them do and which one works best for a certain disease is confusing. This article tells about the difference of x-ray, CT, MRI and ultrasound, and you’ll know which one to choose next time at doctor’s office after reading this.



X-ray film is a common film examination. X-ray has strong penetration, it’s just like taking a photo of the inside of the body. Different body tissues are in uneven density, when radiated, black and white colors will be formed on the film. For example, bones shows white in color and the soft tissue is dark and unclear in the x-ray film.

X-ray is an easy way to check bones and the cost is relatively lower. When patients are likely to have a bone injury from trauma or chronic pain that is difficult to control, doctors will usually recommend an X-ray.

The image of the bone in the X-ray examination is relatively clear, and is generally used to roughly check bone health such as fractures or bone hyperplasia. X-ray examination can only provide two-dimensional images, beside imaging can be affected by clothing, jewelry, or even overly thick soft tissues. Therefore, it is generally used as a preliminary examination.

As you may all know, x-ray is not suitalbe for pregnant women or women who plan to conceive a child in 6 months.


CT Scan

To certain extent, CT is an enhanced version of X-ray. X-ray takes one picture of the body, and CT takes many pictures up and down, layer by layer, therefore CT result is more clear and accurate than that of X-ray. Meanwhile, CT result can be three-dimensional.

In examinations of head, thoracoabdominal, spine, and pelvis, CT is superior to X-ray.  CT examination is of great value in the diagnosis of pulmonary diseases, central nervous system diseases, head and neck diseases, and examination of large vessels.

Despite of all the good sides of CT, everything comes with a price. The problem of CT is that it has higher dose of radiation than X-ray.



Magnetic resonance imaging (MRI) uses a powerful magnetic field to vibrate the water in the body and uses images of the vibrations of water in different tissues to form images that distinguish between normal tissues and diseased tissues. Therefore, nuclear magnetic resonance is also described as “the shaking inspection.”

MRI can randomly cut at any angle without radiation. The inspection on structure of soft tissue is clearer. The display of anatomy and lesions in the brain, spine, and spinal cord is also better than CT.

MRI examination on lungs, bones, fractures is not as good as CT. Sometimes doctors will recommend both. This is to get a more comprehensive understanding of the lesions.

MRI is restricted on people who have metal objects in their bodies, e.g. people with pacemakers, because of the magnetic effect.

MRI is more expensive than CT, actually, it’s the most expensive one in all the four examinations.



Ultrasound can penetrate the human body. When sound waves meet human tissue, they will produce reflected waves. The echo of reflection forms ultrasound image.

Ultrasound is commonly used because it’s of low intensity, high frequency, it doens’t damage the human body, cause no pain, and there’re various display methods for the doctors.

Especially ultrasound is uniquely good in the detection of human soft tissue and the observation of blood flow in blood vessels.

Because of these, ultrasound can be used on pregnant women, even for fractures so as to avoid X-ray radiation.


Ultrasound is not suitable for gas-containing organs such as stomach, or intestines.


Which one to choose ?

A table will help you to know.

X-ray CT MRI Ultrasound Others
Bone, limb √ √ √
Spine √ √
Brain, spinal cord √ √
Chest √ √
Abdominal, pelvic √ √
Heart √ √ √



* The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.