Fluorescence radiography
The Fluoreszenzradiographie is an imaging X-ray methods .
Technical principle
With the classic X-ray image, a film is blackened by X-rays . As a result, objects that are X-ray transparent ( air or clear liquids ) are depicted blackish and X-ray opaque objects are depicted whitish. (However, this weighting is also dependent on the fixing method used during image development.)
In contrast to this, fluorescence radiography uses a fluorescence effect that occurs when X-rays hit a corresponding luminous medium.
history
In the first half of the 20th century, fluorescence radiography (the classic "fluorescent screen") enjoyed great popularity because it made real-time images possible. In contrast, film-based X-ray processes required developing the images, which took a significant amount of time. Smaller orthopedic and gastroenterological doctor's practices could save themselves a photo laboratory and staff.
However, as awareness of radiation hygiene increased, these fluoroscopic methods came under more and more criticism, since the radiation dose was high and the threshold for use was very low.
The process was ultimately obsolete in many areas due to the automated and very fast film development and the obligation to document .
Modern technical application
Today, fluorescence radiographic techniques can be found in many areas of current X-ray procedures. For example, a so-called intensifying screen is integrated in a current recording device behind the X-ray film . When X-rays pass through the film and expose it, they strike this intensifying screen in the continued beam path and make it glow. The emitted light can then expose the film and thus make better use of the X-rays used. It must also be mentioned that classic silver nitrate films can only really use certain X-ray spectra for imaging, but the intensifying screen can also make other spectra accessible for imaging. The disadvantage, however, is that the film is occasionally overexposed by the intensifying screen and the images tend to be blurred.
This technology is also used in image converters (also called BV for image intensifiers ). The problem is that X-rays cannot be recorded electronically directly. X-ray cameras are accordingly a grid of small fluorescent fields with a photocell directly on top . When X-rays hit such a field, it is excited to glow and the photocell on top of it emits an electrical current. Since this signal can in turn be amplified electronically, the term image intensifier is also used for the image converter (conversion of a fluorescent image into an electronic image). Modern image converters work with pulsed images. The radiation dose is delivered in single pulses. When calculating the monitor image , HDR effects can then be brought into play, in which summation effects still enable contrast in areas of high X-ray density , and the number of actually evaluated pulses in heavily overexposed areas automatically reduce. As a result, the image quality can be significantly increased or the radiation dose can be greatly reduced.
Individual evidence
- ↑ Beckelmann: Case Collection Radiology for MTRA