Difference between a CT scan and an MRI scan

August 25, 2015 by Editorial Team

CT and MRI scans are medical tools that are used for diagnostic purposes to produce images of the internal parts of the body. These images help medical personnel determine any abnormalities in a patient’s body, such as injury or tumors. They both achieve the same results but through different ways because of different technologies used.

Definitions

A CT scanner

CT scan stands for computerized tomography. It is a diagnostic technique that uses X-rays to produce internal images of soft parts of the body. The axial tomography rotates, taking several images from different angles. The images are put together by a computer to form 3D images indicating to the physician the details of the tissues being examined.

An MRI scanner
An MRI scanner

An MRI scan, also known as magnetic resonance imaging, is a procedure used to produce images of internal body organs and tissues by employing magnetic fields and radio waves rather than ionization. The MRI scan excites the hydrogen atoms in the body by the use of a magnet that goes around the body. Radio waves are then applied to these hydrogen atoms in a sequential manner. This produces signals which are transmitted to the MRI scanner. A computer processes these signals to create a 3D image of the organs under investigation

Comparison Chart

CT scanMRI scan
Time taken for complete scan is less than 5 minutesTime taken for complete scan ranges from 10 minutes to 2 hours
Risk of radiationNo radiation risk
Suited for bone injuries, lung, chest and cancerSuited for soft tissue evaluation
Uses X-rays for imagingUses large external field, RF pulse and 3 different gradient fields
Images are much clearer with better tissues differentiation and higher resolutionSubtle differences between different kinds of tissues

Comparison

We can compare them in terms of their radiation exposure, effectiveness, suitability, how they produce the image and the quality of the image produced.

  • A CT scan produces images through ionization, hence the risk of radiation exposure. The effective radiation exposure ranges from 2 to 10 mSv whereas MRI does not emit ionizing radiation, and thus there is no risk of exposure.
  • A CT scan takes a very short time for a complete scan, usually about 5 minutes, while an MRI takes longer for a complete scan – from 10 minutes to 2 hours.
  • A CT scan is suited for imaging bone injuries, lung, chest, and cancer checkups. This is because a CT scan can penetrate hard body parts as it uses x-rays. MRI can only be used for scanning soft tissues since it uses magnetic fields which are more suited to soft body parts.
  • A CT scan uses X-rays to produce internal images of the body. MRI employs magnetic fields and radio waves rather than ionization for imaging. A large external field, RF pulse and 3 different gradient fields are used.
  • The images produced by a CT scan are of higher resolution, better quality and offer significant differentiation of the tissues being examined. MRI produces subtle images with little differentiation.

Video

Here is a video on the difference between CT Scan and MRI for more information: