MRI is Magnetic Resonance Imaging and a CT is a Computed Tomography
CT scanner uses X-rays , a type of ionizing radiation, to acquire its images, making it a good tool for examining tissue composed of elements of a relatively higher atomic number than tissue surrounding them, such as bone and calcifications within the body or of structures (vessels, bowel ).
MRI , on the other hand , uses non-ionizing radio frequency signals to acquire its images and is best suited for non-calcified tissue.
CT may be enhanced by use of contrast agents containing elements of a higher atomic number than surrounding flesh(iodine , barium ).
Contrast agents for MRI are those which have paramagnetic properties. One example is gadolinium .
MRI can generate cross-sectional images in any plane including oblique planes.
CT was limited to acquiring images in the axial or near axial plane in the past. The scans used to be called Computed Axial Tomography scans.
However, the development of multi-detector CT scanner to produce data that can be retrospectively reconstructed in any plan with minimal loss of image quality.
For purposes of tumor detection and identification, MRI is generally superior.However , CT usually is more widely available, faster, much less expensive, and may be less likely to require the person to be sedated or anesthetized.
MRI is problematic in case if the patient is having some metallic implant, which will cause interference with the magnetic field.