The science of… medical imaging
CT (computed tomography) is commonly used to look inside the body. It uses X-rays to build up cross-sectional views of the body, which can be used in several ways, including diagnosing bone injuries, looking at the chest and lungs, and detecting tumours.
Advantages of CT
- non-invasive
- generally quicker than MRI
- suitable for patients with metal (implants, etc.) in their body
- less expensive than MRI
- good for looking at bones.
Disadvantages of CT
- requires expensive, specialised equipment
- some people are allergic to the 'contrast' that is drunk before a scan
- uses radiation (more than a typical chest X-ray), and exposure to certain levels of radiation can lead to cancer
- images are restricted to horizontal slices of the body.
MRI (magnetic resonance imaging) is commonly used in hospitals to look at the structures and tissues inside the body - for example, to monitor blood flow and to diagnose or determine how far advanced cancers are. It uses magnets and radio waves to build up cross-sectional images of the body. MRI (and variations of it, such as functional MRI) is also used extensively in biomedical research.
Advantages of MRI
- non-invasive (does not involve cutting into the body)
- does not use potentially harmful radiation
- can get three-dimensional information
- good for capturing a variety of soft and hard tissue types (in contrast to CT, which is mainly good for looking at bones)
- able to capture functional information (e.g. fMRI in neuroimaging).
Disadvantages of MRI
- requires expensive, specialised equipment
- can be claustrophobic for patients
- no metal (including implants and pacemakers) is allowed anywhere near the powerful magnets.
To learn more, see a two-page illustrated guide to the science behind MRI.
This article is part of the online content for ‘Big Picture: Careers From Biology’, which includes interviews with a scientific researcher who uses MRI in her work and an assistant practitioner in a radiography department. Download the PDF.
Image: A digitally enhanced MRI scan of the human head. Credit: Mark Lythgoe and Chloe Hutton, Wellcome Images.