Duration, procedure and risks of a CT

Quick overview: Frequently asked questions

What is the difference between MRI and CT? A CT scan is performed using X-rays, while an MRI scan uses magnetic fields and radio waves. There is therefore no radiation exposure with an MRI scan – but CT is still better suited for some examinations.

What is done during a CT scan? The body is examined layer by layer using X-rays so that a three-dimensional image can be created.

How long does a CT scan take? Depending on the body region to be examined, a CT scan can take between a few minutes and half an hour.

What can a CT scan reveal? Computer tomography can be used to precisely depict the inside of the body. This makes it possible to detect tumors, bone fractures, and acute and chronic illnesses.

At a glance:

What is a computed tomography scan?

A CT (abbreviation for computer tomography or computed tomography) is a special X-ray procedure that produces detailed cross-sectional images of the body.

Several images of an organ or a specific body region are taken from different directions and combined by a computer to create a detailed image (the so-called computer tomogram). This technique is therefore also known as layer X-ray.

Unlike conventional X-rays, a CT scan does not only radiate the body from one direction (which creates a simple, two-dimensional image) – this makes it possible to create three-dimensional images.

This allows even the smallest changes in the body to be detected at an early stage. This is why computer tomography is an indispensable imaging procedure, especially in cancer diagnostics.

But CT is also frequently used in the diagnosis of other internal diseases and injuries or for planning or monitoring the progress of treatments.

How does computed tomography work?

A CT scanner is a device with a rotating ring through which the patient is moved on a couch. This ring contains an X-ray tube and a detector system.

The tube sends out rays that pass through the body and are picked up by detectors on the other side of the body. The computer uses the difference between the transmitted and received radiation to determine the density of the tissue that has passed through and to create a series of three-dimensional cross-sectional images.

The denser the tissue, the less radiation it lets through and the brighter it appears in the image. Bones that are very dense therefore appear particularly bright.

How does a CT scan work?

A CT scan is a painless and silent examination that takes between a few minutes and half an hour, depending on the body region.

Due to radiation exposure, the medical staff is in the next room during the recording, but is in constant contact with the patients via a window and an intercom.

The patients are placed on an examination table for the CT scan. Before the examination begins, a venous access may be placed in the hand or in the crook of the elbow, through which contrast medium can be administered during the examination. This increases the contrast in the images, making it easier to distinguish between different tissue structures.

The table is then slowly moved through the ring-shaped opening of the CT scanner. This opening is so large that there is no feeling of tightness.

During the examination, patients should not move as much as possible to ensure optimal image quality. For certain examinations, it may therefore be necessary to hold your breath briefly.

The images obtained are combined by the computer to create a three-dimensional image and then evaluated by a radiologist.

What should be considered before and after a CT scan?

Iodine-containing contrast media may be used in certain diseases such as

should only be administered with caution. Therefore, the doctor asks the patient in advance about previous illnesses, allergies and current medication.

Since CT is based on X-rays, it involves a certain amount of radiation exposure. Depending on the body region to be examined, patients are given special covers to protect adjacent body areas from scattered radiation.

For certain examinations, it may be necessary to appear for the CT scan on an empty stomach. If contrast agents were used for the CT scan, you should drink plenty of fluids after the examination to help excrete the contrast agent through the kidneys.

When do you need a CT scan?

A CT scan is usually performed as part of the diagnosis. However, the necessity of the examination should be discussed in advance in order to avoid duplicate examinations and thus increased radiation exposure.

For the same reason, a distinction is made between examinations of the entire body (whole-body CT) and specialized images of certain body regions – such as cardiac CT, skull CT, lung CT or abdominal CT.

Due to the short examination time, computed tomography is particularly valuable when every second counts – for example,

• severe head injuries,
• Suspected stroke or
• in the case of seriously injured accident victims.

In addition, CT is used for acute and chronic diseases of the chest and abdominal organs (such as intestinal inflammation, mechanical intestinal obstruction, and liver and lung diseases). With the administration of contrast agents, large vessels (such as the aorta) can also be clearly visualized.

Computed tomography is also an essential component in tumor diagnostics and follow-up examinations of cancer patients.

Risks and side effects of a CT scan

Computed tomography is a relatively low-risk routine procedure, but in rare cases unwanted side effects can occur:

• Contrast agent can cause temporary sensations such as tingling or a feeling of warmth. In rare cases, severe intolerance reactions or impairment of kidney or thyroid function can occur.

• The radiation dose during a CT scan is higher than during normal X-rays. This radiation can theoretically cause cancer years later, but the risk is statistically low.

Due to the X-rays involved, computer tomography is not suitable for pregnant women – ultrasound (sonography) or magnetic resonance imaging (MRI) must be used instead.