How it works
An MRI uses a powerful magnet and radio waves to produce images of the internal parts of your body.
A CT machine sends X-ray beams through the body, taking many 2D pictures from various angles, which a computer later joins together to form a 3D image.
Doughnut-shaped machine with a hole in the middle, mostly closed on the other end. (Closed MRI, most powerful)
Doughnut-shaped machine with a hole in the middle, open on both sides.
Check the magnet strength denoted by ‘T’ for Tesla. Today, a 3T MRI (closed MRI) is the most widely accepted MRI scanner that produces images of maximum clarity.
In CT machines, the greater the number of ‘slices’, the sharper the quality of the scan. For example, a 128 slice CT machine produces very clear images as compared to a lower slice CT scanner.
An MRI scan is required when images need to be detailed. An MRI scan offers more soft tissue image and bone details than a CT scan. Especially in the case of strokes, tumours, etc. MRI scans show the difference between normal and abnormal tissue.
A CT scan is used when speed is important: for example, in the case of trauma and stroke.
CT scans enable imaging of bone, soft tissue and blood vessels at the same time, but they are not as detailed as an MRI – for example, a CT scan can pinpoint size and location of tumours but does not show differences between normal and abnormal tissue.
Since the MRI scanner is closed on one end, many patients suffer from claustrophobia during the scan.
However, newer 3T MRI scanners with ambient experience reduce the incidence of claustrophobia by allowing patients to see movies during the scan and creating an illusion of more space and light.
Claustrophobia is not an issue since the scanner is open on both sides.
Magnets and radiation
An MRI has no ionizing radiation since it works on magnetic fields and radio waves
Though a CT scan uses X-rays, its radiation dose is small enough to be negligible.
However, CT scans may not be recommended for pregnant women or very small children.
Average Duration: 7-20 minutes
Average Duration: 5-15 minutes
Caution to be taken
Since the MRI has a powerful magnet, NO METALLIC OBJECTS should be taken inside the MRI room. Also, never enter the MRI room without a staff member accompanying you – remember, the MRI magnet is always ON, it is never switched off.
People with metal implants like pacemakers, cardioverter defibrillators, etc. can undergo a CT scan. However wearing other metal items should still be avoided, since they will interfere with the scan quality.
No fasting required, even for scans with contrast
If patient is getting a CT scan with contrast, he/she will be required to fast for 3 hours prior to the scan
If you’re advised to get a scan with contrast, a dye will be injected into your body. This dye helps highlight the internal structures of your body better, making a more accurate diagnosis possible. The dye is generally a gadolinium dye and is injected through an intravenous canula inserted in the vein in your hand.
CT scans can also be done with contrast. In this case, typically an iodine-based or barium-sulfate-based agent is administered. This dye is either ingested or injected into the vein of the hand through an intravenous canula.