Diagnosis: what are the differences between x-ray, CT and MRI

For the diagnosis of diseases or for research in neurology, doctors use so-called imaging methods to take a look inside the body. Known techniques such as X-ray, CT and MRI are considered indispensable. "These methods differ fundamentally in their methodology. Which systems support diagnostics depends on which parts and areas of the body need to be examined, ”explains Dr. med. Inga Cruse, radiology specialist at radprax Wuppertal.

Translucent shots

X-rays are the simplest and oldest of the three examination methods. Radiologists produce two-dimensional images of a specific body region within milliseconds. X-rays penetrate the body and then hit a special, undeveloped film or - in the case of so-called digital X-rays - an imaging detector. In both cases, the incoming radiation leads to a blackening of the image, which depends on the permeability of the different tissue structures to X-rays. "Changes such as broken bones, foreign bodies or, for example, pneumonia can thus be ideally reproduced," explains Dr. Cruse on. Nowadays, medical professionals are increasingly relying on digital X-rays, which are evaluated directly on the computer and require a significantly lower radiation dose.


Doctors use computed tomography, or CT for short, to display internal organs, and in particular for emergency examinations, for example in the case of accident victims or stroke patients. 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 creates images of all regions of the body which - in contrast to conventional X-rays - reproduce internal organs and body structures without any overlap. With appropriate examination technology, the images can also be reconstructed three-dimensionally, which supports successful operation planning. Contrast agents also help to differentiate between different tissue structures or vessels in the images.

Analyzing magnetic field

In contrast to X-rays and CT, magnetic resonance imaging, also called MRI, does not require radiation. A strong magnetic field that evaluates the movements of the hydrogen atoms in the body provides a three-dimensional image. Patients feel nothing of this process and are also in a tube during the 15 to 30 minute examination. Since an MRI can show soft tissues and fluids much better than other methods, doctors use this method especially for the examination of internal organs, joints and intervertebral discs. This method is also used in cardiac diagnostics and for the diagnosis of brain diseases. "Switching the gradients on and off, i.e. the magnetic fields, creates a certain background noise, but thanks to improved technologies, this is significantly reduced," explains the radprax expert. Due to the active magnetic field, this method was previously not an option for people with pacemakers, insulin pumps or cochlear implants. Nowadays, however, various manufacturers also offer MRI-compatible pacemakers and cochlear implants.

“All three procedures complement each other in the diagnosis of diseases. We are dependent on the different perspectives, particularly in the case of complicated disease courses. This is the only way to form a complete picture and initiate the appropriate therapy, ”explains Dr. Finally, Cruse.

Author and source information

Video: MRI: Basic Physics u0026 a Brief History (August 2020).