What Is the Difference Between MRI & CT Scans?

Updated July 19, 2017

When health care providers need to see inside the human body, X-ray technology is usually used in detection of skeletal structures and high-density vital organs. But the latest technologies utilise magnetic resonance imaging (MRI) and computerised tomography (CT) scanning technology to achieve highly detailed visualisations of body structures in two and three dimensions. Radiologists are trained on the use of the most appropriate imaging techniques for diagnosis and treatment.


MRI scanners are typically room-sized cylindrical tubes in which a patient is inserted lying down on a flat surface. Besides the size being somewhat imposing, the machines make a great deal of noise while operating. The sounds are produced by the very large magnets rotating within the body of the instrument.

CT scanners are relatively quiet in operation and are available in several configurations. For instance, a large, doughnut-shaped scanner is used primarily for head examinations. Depending on the configuration, the patient can be positioned on a chair, couch or flat surface.


MRI scans use large magnets and radio waves to create two- and three-dimensional images. The massive magnetic field they produce causes the cellular nuclei to resonate in a fashion that radio waves can detect. MRIs are relatively harmless to the patient since they do not use X-rays or radiation ionisation. To produce images, an MRI scan usually takes 30 to 90 minutes, with the patient remaining motionless.

CT Scans or "Cat Scans," use several X-ray beams that produce high-ionising radiation to obtain two- and three-dimensional images. CT scans have the advantage of speed over MRI in most applications.

In order to obtain clearly defined images in both types of machines, the patient may be given an oral or injected contrast agent to highlight and refine the images.


MRI scans are used primarily for diagnosis and in guiding interventional surgery in some instances. They provide extreme detail in neurological, musculoskeletal, cardiovascular and soft-tissue diagnosis.

CT scans are best at providing images of the hard, skeletal bone structures. They are also used in imaging soft tissues and blood vessels.


During a MRI procedure, the patient must remove all metal objects. Hip implants, pacemakers and other metal in the patient can cause serious repercussions if hospital personnel are not aware of their presence. Since the patient must remain still for long periods for time, positioners are often used to help in immobilisation. To relieve the possible discomfort of the loud noise produced by the magnets and the somewhat claustrophobic environment of the tube, a mild sedative and/or music headphones may be provided. There is no physical pain involved other than perhaps at the contrast media injection site.

CT scans are fast and efficient, especially in emergency situations. The primary drawbacks are the quality of imaging in "softer" tissues and the risks associated with high-ionising radiation in a patient who has had frequent exposures to X-rays.


Consult your physician for a full description of precautions and warnings before undergoing either type of scan. It is generally advised that pregnant women avoid both procedures.

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About the Author

Ken Appelt is a senior sales and marketing executive with experience that includes product design, research, production, quality assurance, distribution and education. He has been writing and publishing articles in since 1982, mainly in healthcare, medical device and scientific periodicals. He holds a Bachelor of Science in chemistry from the University of Wisconsin and a Master of Business Administration from Lake Forest.