What’s the difference between an MRI and CT scan?

Diagnostic imaging techniques offer a powerful tool to help doctors diagnose a range of conditions. The most common imaging methods used today are computed tomography (CT) scans and magnetic resonance imaging (MRI) that assist in focusing on soft tissues, bones, and blood vessels. To most people, these procedures may look similar at a first glance; however, in reality MRIs and CT scans differ vastly when it comes to their overall functionality, the imaging they provide and for what they’re used to diagnose.

 

Working methodology

 

In a CT scan, X-rays are used to create detailed pictures of organs, bones, and other tissues. The CT scanner emits a series of narrow beams through the human body to get a more detailed final picture of the inside of your body. The data is transmitted to a computer which helps build a 3-D image of the different parts of the body, making it easier for the doctor to recognize the issue. In an MRI, a magnetic field helps create detailed pictures of the body. An MRI is a non-invasive procedure which doesn’t use any radiation, unlike X-rays. 

 

Purpose of a CT scan

 

A CT scan is ordered by doctors to identify the following conditions:

 

Circulation problems: Blood vessel blockages, kidney problems, heart disease, pulmonary edemas and aortic aneurysms.

 

Abdominal abnormalities: Unknown masses in the liver, pancreas, or kidneys

 

Lung issues: To identify the signs of fibrosis, emphysema, tumour, pleural effusion, collapsed lungs and more.

 

Skeletal system problems: To view complex fractures, osteoporosis damage and bone tumours.

 

Head conditions: Haemorrhages, brain calcification, tumours and blood flow problems to the brain.

 

Purpose of an MRI scan

 

An MRI is a scan that helps identify the following conditions:

 

Brain: An MRI is a preferred modality to identify brain tumours as it shows hard-to-reach areas of the brain. It is also a preferred choice for conditions including multiple sclerosis, stroke, Alzheimer's disease and epilepsy.

 

Musculoskeletal system: Musculoskeletal MRI is often used to diagnose and monitor joint and muscle disease.

 

Gastrointestinal system: Apart from the liver and pancreas, an MRI helps assess inflammatory bowel disease and bowel tumours.

 

Blood vessels and the heart: MR imaging of the arteries of the heart help identify any abnormal narrowing or vessel wall dilatations. It is the gold standard for assessing myocardium in patients with heart disease.

 

Advantages of an MRI over CT scan

 

Radiation exposure: A CT scan uses ionizing radiation. The effective radiation dose from diagnostic CT procedures is in the range of 2 to 10 mSv - the same as the average person receives from background radiation in 3 to 5 years. However, in an MRI scan, there is no use of ionizing radiation. It is a preferred method in children and patients requiring multiple imaging examinations.

 

Higher detailing: An MRI scan is more detailed in its images. It offers better images of soft tissue, ligaments, or organs. 

 

Better in detecting soft tissue changes: MRI is a better option than a CT scan when it comes to soft tissue damage, torn ligaments, and herniated disks.

 

More sensitive: MRI is more sensitive and specific for abnormalities within the brain. An application of contrast helps increase the sensitivity of imaging. 

 

Can be performed in any imaging plane: MRI has the advantage of being able to visualize anatomy in all three planes: axial, sagittal and coronal, without having to physically move the patient.

 

While an MRI scan produces a better overall image of the tissue under examination, a CT scan is preferred when it comes to scanning larger areas. However, a doctor can give the best opinion when it comes to choosing the best scan for you. 

 

Reviewed by: Dr. Deepak Garg, Consultant - Radiology, House of Diagnostics