Diagnosis What are the differences between X-ray, CT and MRI?

To diagnose diseases or even for research in neurology, physicians use so-called imaging techniques to look inside the body. Known techniques such as X-ray, CT and MRI are considered indispensable. "These procedures differ fundamentally in their methodology. Which systems support diagnostics depends on which body parts and areas need to be examined, "explains Dr. med. med. Inga Cruse, Specialist in Radiology, from radprax Wuppertal.

The diagnosis of external wounds is often completed with a gaze diagnosis. For internal wounds, most imaging procedures such as ultrasound, CT or MRI are appropriate. (Image: Tyler Olson / fotolia.com)

Translucent shots

The X-ray is the simplest and oldest of the three examination methods. Within milliseconds, radiologists produce two-dimensional images of a specific body region. X-rays penetrate the body and then hit a special, undeveloped film or - in the so-called digital X-ray - on an imaging detector. In both cases, the incoming radiation results in blackening of the image, which is dependent upon the transmission of the various X-ray tissue structures. "Changes such as broken bones, foreign bodies or, for example, pneumonia can thus be ideally mapped," explains Dr. Cruse up. Today, physicians increasingly rely on digital X-ray, which is evaluated directly on the computer and requires a significantly lower radiation dose.

Lying knowledge

For the representation of internal organs and especially in emergency examinations, for example in accident victims or stroke patients, physicians rely on computed tomography, CT for short. Patients lie in a tube in which X-rays depict cross-sections of the body within a few minutes. The subsequent virtual composition of the images on the computer produces images of all body regions which - in contrast to conventional x-rays - reproduce internal organs and body structures without overlapping. With the appropriate examination technique, the images can also be reconstructed three-dimensionally, which supports successful surgical planning. Contrast agents also help distinguish different tissue structures or vessels in the images.

Analyzing magnetic field

In contrast to X-ray and CT, magnetic resonance imaging, also called MRI, does not involve radiation exposure. Here a strong magnetic field, which evaluates the movements of the hydrogen atoms of the body, provides a three-dimensional picture. Patients feel nothing of this process and lie in a tube during the 15- to 30-minute examination. Since an MRI can represent soft tissue and fluids much better than other procedures, medical professionals use this method, especially for the examination of internal organs, joints and intervertebral discs. This procedure is also used in cardiac diagnostics and for the diagnosis of brain diseases. "Switching on and off the gradient, ie the magnetic fields, creates a certain amount of noise, but thanks to improved technologies, it is significantly reduced," explains the radprax expert. Due to the active magnetic field, this method was previously out of the question for wearers of cardiac pacemakers, insulin pumps or cochlear implants. Today, however, several manufacturers also offer MRI-compatible pacemakers and cochlear implants.

"All three procedures complement each other in the diagnosis of diseases. Especially with complicated disease processes, we depend on the different perspectives. This is the only way to form a complete overall picture and to initiate appropriate therapy, "explains Dr. med. Cruse concluding.