Image Acquisition and Display
Images can be acquired in several different ways depending on the equipment used by any particular imaging department. These are:
• conventional film/screen technology;
• fluoroscopy/fluorography;
• digital imaging:
– computed radiography (CR);
– direct digital radiography (DDR).
Each of the above will be considered briefly.
An image captured on photographic film will have high resolution, although it has narrower exposure latitude compared with other image-capture systems. This means that the radiographer has much less margin for error when selecting exposure factors before making an exposure. It is relatively easy to overexpose or underexpose an image compared with other image-acquisition devices.
• conventional film/screen technology;
• fluoroscopy/fluorography;
• digital imaging:
– computed radiography (CR);
– direct digital radiography (DDR).
Each of the above will be considered briefly.
Conventional film/screen technology
At the time of writing, this is the cheapest and most versatile method of image capture. Photographic film is capable of storing an image alone, but the exposure required can be reduced considerably if the film is placed between intensifying screens that convert the X-ray energy into light, which in turn exposes the film. The film and cassettes are widely available in a variety of sizes and can be used with almost any piece of imaging equipment.An image captured on photographic film will have high resolution, although it has narrower exposure latitude compared with other image-capture systems. This means that the radiographer has much less margin for error when selecting exposure factors before making an exposure. It is relatively easy to overexpose or underexpose an image compared with other image-acquisition devices.
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A variety of systems are available in which the screen and film can be varied to suit a particular task. Thus, the speed and resolution can be changed in any given clinical situation by selecting a different film and screen. Graduated or asymmetric systems have been used to enhance spine and chest radiography, where
the subject contrast is high.
X-ray film is highly portable, although a considerable amount of space is required to store the film bags.
A series of X-ray film processors are required in a department using conventional imaging technology. These must be regularly cleaned, serviced and subjected to a rigorous quality-control programme in order to ensure consistency of performance.
Fluoroscopy/fluorography
capture images, which are then displayed in real time or as static
images on a monitor. Fluoroscopy is very useful for following the progress of contrast agent around the body, but its resolution is poor compared with that of other image-acquisition methods so it is not currently used for plain radiographic imaging. Fluorography employs photographic film to capture the image from the image intensifier. This method has now been largely superseded by digital image-capture methods.