Quick version
What is a CT scan?
CT stands for computed tomography and is sometimes referred to as CT or CAT scan. In a CT examination, X-rays are used to take a large number of cross-sectional images, which are then combined by a computer into a 3D image. The examination is quick to perform, usually only a few minutes.
How does CT work?
The X-rays pass through the body and are captured by multiple detectors in the equipment. Different tissues in the body absorb radiation to varying degrees, which provides detailed images of, among other things, the skeleton, lungs, and organs.
What is an MRI scan?
During an MRI scan, the equipment creates a strong magnetic field and uses radio waves to produce detailed images of the body's soft tissues — completely without radiation.
How does MRI work?
The body consists largely of water, and MRI makes clever use of this. When the magnetic field is activated and radio waves are sent into the body, the hydrogen atoms in the water molecules emit signals that the computer converts into images of soft tissues, the brain, spinal cord, and joints.
How do you know which examination is needed?
The choice between CT and MRI depends on the symptoms you are experiencing and what the doctor wants to examine more closely. CT is often the first choice when a quick overview is needed or when acute changes are suspected, while MRI is used when detailed images of soft tissues are required or when radiation should be avoided. The ability to lie still, as well as implants and metal objects in the body, may also influence the choice.
When is CT most suitable?
CT is often the most effective method for:
- Injuries to bones or organs
- Suspected brain hemorrhage
- Suspected pulmonary embolism (blood clot in the lung)
- Severe or unclear injuries in the abdomen or chest
- Assessment of fractures and bone injuries
When is MRI most suitable?
MRI is often used for:
- Examination of the brain and nervous system
- Injuries to muscles, tendons, and ligaments
- Back problems involving nerve compression
- Long-lasting or recurring joint problems
Advantages and disadvantages
Advantages and disadvantages of CT
The advantages of CT are that it is a very fast examination, allowing assessment within a short time. The scan provides detailed images of the skeleton and organs and is best suited for situations where time is critical, such as in acute illness or trauma.
The disadvantages are that CT provides poorer soft tissue contrast compared to MRI and that the body is exposed to ionizing radiation.
Advantages and disadvantages of MRI
The most obvious advantage of MRI is that the body is not exposed to any radiation. The method provides more detailed images of soft tissues and is better suited for examining the brain, spine, and joints.
Disadvantages of MRI include that the examination takes significantly longer than a CT scan—usually around 20–60 minutes depending on the scope of the exam. Some people may also find the examination uncomfortable or feel confined in the tunnel. Due to the strong magnetic field, MRI is also not suitable for individuals with certain types of metal implants.
