Computed tomography (CT)

Overview: What is computed tomography?

Computed tomography (CT) is an imaging procedure in which X-rays are used. In medical diagnostics, CT is routine in all radiology practices and hospitals. In computed tomography, radiologists display the body “in slices” and generate high-resolution cross-sectional images in various shades of gray.

For example, organs such as the heart, brain, lungs or liver, but also hard structures such as bones and joints can be visualized well. Soft tissue such as connective tissue, muscles, tendons and blood vessels can also be imaged. Sometimes we administer a contrast agent containing iodine during the examination to make pathological changes and vessels even more visible.

During the examination, patients lie (comfortably and quietly) on a couch that is pushed through a large, wide ring – the CT scanner. Even people with claustrophobia can perform the examination without any problems.

Computed tomography is a painless examination that is usually over quickly – depending on the type of medical issue. Since it works with X-rays, there is a certain amount of radiation involved, but this is considered to be low. Always discuss with your doctor whether the examination is really necessary and whether there are any radiation-free alternatives.

How does computer tomography work?

A computer tomograph is a device that has a rotating ring. During the examination, he or she turns around the patient. An X-ray tube is integrated into one half of the ring, which generates a fan-shaped X-ray beam. This penetrates the body. The respective structures attenuate it to varying degrees – depending on the nature, density and thickness of the fabric.

In the opposite half of the ring there is a measuring system (detectors) which catches the radiation and converts it into signals. These are sent to a computer and converted into three-dimensional images – the computer tomogram. Radiologists can view and assess the images on a monitor in various shades of gray or in color. Changes and abnormalities can thus be recognized very precisely.

In contrast to conventional X-ray examinations, the patient is not only irradiated from one direction. Because the X-ray tube rotates around the person being examined, CT images can be taken from several sides. The body is scanned layer by layer, producing detailed cross-sectional images.

Computed tomography - the procedure

Computer tomographs have a large ring. The MTRA guides the patient on the table into the device through the hole in the middle. Most of the body is located outside the ring. Depending on the medical question, the duration of a CT scan is between two and 15 minutes.

This is roughly how the process can be described:

• You take a seat on a lounger. You should lie there as comfortably and quietly as possible during the examination – otherwise the images could be “blurred” and out of focus.
• Although you are alone in the examination room due to the X-ray radiation, you are connected to the radiology assistant at all times via an intercom system. So you can always get in touch with them.
• The stretcher is pushed through the large ring via a rail.
• The X-ray machine rotates around your body. It scans all areas of the body that the doctor wants to know about, layer by layer. Sometimes you will be instructed to hold your breath for a few seconds in between. This is necessary for a CT scan of the lungs or upper abdomen, for example. Sometimes we also use an iodine-containing contrast medium in order to be able to assess certain structures even better.
• A measuring system opposite the X-ray tube receives the radiation reflected by the various body structures. The signals are more or less attenuated, depending on the density of the tissue. Bones, for example, have a high density and attenuate the rays more than air-filled tissue, such as the lungs or intestines.
• A computer compiles a three-dimensional, complete image of the examined organ or structure from the measured values. Fabrics of different densities appear in different shades of gray.

Areas of application: When is computed tomography used?

Computed tomography has many different areas of application. This allows many organs, tissues and structures to be visualized directly and realistically within a few seconds. This enables us to diagnose a wide range of illnesses and injuries. Even though CT is a more expensive imaging procedure compared to classic X-rays, it is now a standard in the diagnosis of diseases and injuries.

CT is used in the following cases, for example:

• Brain diseases: e.g. stroke, cerebral hemorrhage, tumors, skull base fracture
• Injuries to bones and joints, for example after an accident: Doctors can detect complicated bone fractures, for example.
• Diseases of the abdominal organs (e.g. liver, spleen, pancreas)
• Lung diseases
• cancers: This allows us to determine the location, size and spread of a tumor – the subsequent treatments depend largely on this. Metastases in the organs and lymph nodes can also be diagnosed.
• Foci of infection and inflammation, such as liver and intestinal inflammation (e.g. Crohn’s disease, ulcerative colitis)
• Cardiac and vascular diagnostics, such as the diagnosis of coronary heart disease, heart valve defects or dilations of the arteries of the entire body
• Injuries and accidents, such as fractures and organ injuries in e.g. traffic or sports accidents
• Planning operations – CT scans provide us with a precise overview of the type and location of injuries and diseases – so you can plan the surgical procedure in advance.
• CT as support for other examinations, for example when taking a tissue sample (biopsy). One example is the prostate biopsy, which plays a role in the diagnosis of prostate cancer. We also often use CT to perform a puncture to drain fluid. And an angiography to visualize the vessels (e.g. aneurysm in the brain, peripheral arterial occlusive disease = PAOD) is often more informative if we combine it with a CT scan.

Computed tomography: advantages and risks

Computed tomography has several advantages over “normal” X-ray examinations.

Examples are:

• We can visualize almost all organs and tissues directly and realistically.
• The pictures are very accurate and detailed.
• CT provides very fast and informative examination results.
• CT poses no problems for people with claustrophobia.
• CT also works if you have a pacemaker or a metal implant.
• CT can be easily combined with other examination methods, such as angiography or (very expensive) positron emission tomography (PET-CT)

However, CT also harbors some risks. The procedure has the following disadvantages:

• CT works with X-rays. This is higher than with a conventional X-ray examination. However, we classify the dose used and the potential health risks as very low and harmless. Nevertheless, you should always discuss with your doctor whether the examination is really necessary.
• Side effects may occur when using contrast media. Minor complaints such as discomfort, a feeling of warmth or nausea are possible. However, some people are hypersensitive and allergic to iodine-containing contrast media. This risk has decreased with newer contrast media. Always have possible intolerances clarified before the examination. Contrast media containing iodine may not be suitable in the case of kidney disease and hyperthyroidism.
• Computer tomography is not suitable for pregnant women due to the X-ray radiation. It is only used if there is no other diagnostic option.