X-ray phantom

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An X-ray phantom is a phantom body with special structures that are imaged on an image receiver when X-rays are transmitted . In medical X-ray diagnostic devices, such phantom bodies are used instead of the patient to control the image quality and to adjust the X-ray devices.

Design and structures

In contrast to the changing structures in the patient, the X-ray phantom contains constant ones in general. optically visible object structures that can be compared with their image in the X-ray image during fluoroscopy or recording. The image quality can be controlled via the differences between the depicted and the original structures and, if necessary, the X-ray device and the image generation system can be readjusted.

The X-ray phantom generally consists of Made of a base made of acrylic glass or aluminum, in which either reproduced body parts (bones and organs) or geometrically regular measuring structures (generally made of thin lead and copper templates) are built. Similar to a TV test image, these measurement structures contain a grid with specific format markings, density levels for different gray values ​​and fine line grids. In this way, distortions, image scale, optical density (of blackening and contrast) as well as the resolution of fine image structures can be assessed in the test image.

With the help of a densitometer, a dosimeter and a length scale, exact physical measurements (in accordance with DIN 6868 standards) of image quality and radiation exposure can be made. Such measurements are carried out as part of an acceptance test of the X-ray device and a regularly repeated constancy test for quality assurance in accordance with Section 16 of the X-ray Ordinance (RöV).

In legal regulations and technical standards, such an X-ray phantom is generally referred to as a test body (in English: test phantom). Artificial parts of the human body are generally used in medicine. as a "phantom" and in technology as a "dummy", e.g. B. Crash test dummy called. The term X-ray phantom is used to distinguish it from other types of phantom known in medical physics such as water phantom or arm phantom .

history

From the very beginning (since the 1930s) there have been test images for television pictures to check the picture quality. For the much older medical X-ray images, compact test specimens were only created after 1980 - before that, the patient himself often served as an object for taking test images. The problem is the other type of imaging with invisible X-rays . The test pattern cannot simply be drawn on paper, as is done to test television transmission (with reflected light). To generate a test image with transmitted X-ray radiation, a suitably structured body must be built that weakens the X-ray radiation in a defined manner like the body part of a patient and additionally contains measurable structures for imaging.

Prototypes of a test body with integrated structures were developed by Bronder at the beginning of the 1980s in the Berlin Institute of the Physikalisch-Technische Bundesanstalt. In 1982 the first compact test body for X-ray diagnostic equipment was presented. For the first time, a test specimen with an attenuation equivalent to that of the human body contained all of the structures that were important for the creation of an image in a compact design, firmly aligned next to one another. Its main body is made of aluminum, which, if it is thin, weakens the radiation to the same extent on average as the human body. The compact test body provided with a handle can easily be handled on medical X-ray diagnostic devices, with the integrated imaging structures remaining firmly adjusted to one another.

Several similar test specimens were created in quick succession, the physical properties and structures of which differed more or less from one another.

After the measuring and testing facilities had been created and tested, legal provisions for regular control of medical X-ray diagnostic equipment to ensure image quality and to protect the patient from ionizing radiation were included in the X-ray Ordinance in 1987. It is about the goal of the best possible image quality with the lowest possible radiation exposure of the patient.

Today there are various other test bodies as X-ray phantoms for the various special X-ray diagnostic facilities in dentistry (panoramic images), mammography or with digital X-ray image creation.

literature

  • A. Bäuml (Ed.): Quality Control and Assurance in Diagnostic Radiology. Materials for a WHO Training Workshop Neuherberg Oct. 27 - Nov. 3, 1982. (= ISH issue 38). Institute for Radiation Hygiene of the Federal Health Office, Neuherberg 1984.
  • H.-S. Stender, F.-E. Stieve (Ed.): Practice of quality control in diagnostic radiology. Symposium on October 15 and 16, 1983 at the Hannover Medical School . Gustav Fischer Verlag, Stuttgart 1986.
  • T. Bronder, R. Heinze-Assmann: Quantitative evaluation of film-foil combinations for X-ray diagnostics. In: Physics in Medicine and Biology . Volume 33, No. 5, May 1, 1988, pp. 529-539. doi: 10.1088 / 0031-9155 / 33/5/002

Web links

Individual evidence

  1. ↑ Th. Bronder: Test specimen for quality control in X-ray fluoroscopy equipment. In: PTB annual report 1982. Braunschweig 1983, pp. 225–226.
  2. ↑ Th. Bronder: Uniform measurement phantom for X-ray diagnostics. In: Th. Schmidt (Ed.): Medical Physics 1984. 15th Scientific Conference of the German Society for Medical Physics, Nuremberg, Sept. 27 and 28, 1984 . Hüthig, Heidelberg 1985, pp. 321-324.
  3. ↑ H. Eder: Quality control in X-ray diagnostics by means of a universally applicable test body. In: Fortschr. Röntgenstrasse 13, 5, 1983, pp. 556-561.
  4. ↑ M. London: Test body for quality assurance in X-ray diagnostics. In: X-ray practice. 43, 1990, pp. 5-14.