Citation, DOI and article data. Murphy, A. Image intensifier. Reference article, Radiopaedia. URL of Article. Overview After the x-ray beam emerges from the patient, it enters the image intensifier tube through the input window and is partially absorbed by the fluorescent input screen entrance phosphor creating a number of light photons.
Quiz questions. Stewart C. Arnulf Oppelt. Jerrold T. John C. Heggie, Neil A. Liddell, Kieran P. Applied Imaging Technology. Image intensifiers can electronically vary the size of the input radiation field of view whilst keeping the output field fixed, equal to 2.
If the input field of view is halved, then the size of the patient being viewed is also halved which results in a two fold magnification of the image. This type of magnification, known as electronic zoom, doubles the spatial resolution performance.
Figure H. Image intensifer TV system with 4 FOV diameters: 37 cm, 30 cm, 22 cm, 17 cm, and corresponding intrinsic resolution capabilities bar pattern is taped next to input phosphor of the image intensifier. Top row shows full FOV image, and bottom row shows bar pattern magnified view.
If the input field of view is halved, then only one quarter of the input phosphor is being irradiated since the area is proportional to the square of the field of view. Halving the input field of view, while keeping all the other parameters constant, would reduce the image brightness to a quarter of the original brightness at the full field of view.
To compensate for this effect, the amount of radiation that is incident at the input of the image intensifier needs to be quadrupled to compensate for reduction in exposed area. The consequence to the patient is an increase in the dose when the "magnification mode" is utilized, but also spatial resolution enhancement.
Figure I shows a single frame from a fluoroscopy run using an image intensifier diameter of 38 cm; Figure J shows an magnified image electronic zoom with an image intensifier diameter of 25 cm and Figure K shows further magnification achieved by reducing the image intensifier input diameter to 15 cm. Relative to the image in Figure I, the magnification in Figure J is x 1.
The choice of technique in Figure I was 75 kV and 2. When the image was magnified by a factor of 1. When the image was magnified by a factor of 2. Use of magnification modes in fluoroscopy is usually associated with an increase in the choice of x-ray tube voltage for two reasons:.
By contrast, maintaining a constant x-ray tube voltage with an increase in magnification of x 2. Figure L shows the digital photospot image that corresponds to the fluoroscopy frame depicted in Figure I i. Increasing the magnification by a factor of 1. A further increase in image magnification to x 2.
The x-ray image intensifier converts the transmitted x rays into a brightened, visible light image. Within an image intensifier, the input phosphor converts the x-ray photons to light photons, which are then converted to photoelectrons within the photocathode.
The electrons are accelerated and focused by a series of electrodes striking the output phosphor, which converts the accelerated electrons into light photons that may be captured by various imaging devices. Through this process, several thousand light photons are produced for each x-ray photon reaching the input phosphor.
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