Computed radiography (CR) systems use an image plate of photostimuable phosphor crystals that replace traditional film in a cassette. When the plate is exposed to x-rays, the energy is absorbed and stored by the crystals .The cassette is placed in a CR reader, where the energy is released by exposing the plate to a laser beam. This light energy is collected by photomultipliers, converted to electrical charges, and then converted to a digital image.
 
     Direct Radiography (DR) systemsutilize a variety of media to convert x-rays into digital images. Under the umbrella of DR are both direct and indirect detector technologies.Direct detector systems employ amorphous selenium, lead oxide, lead iodide,thallium bromide, or gadolinium mixtures.These materials act as a photoconductor that converts x-ray photos into an electrical charge,which is then converted into an electrical charge,which is then converted into a digital image by an analog-to-digital converter.Indirect detector DR systems use charge-coupled device (CCD),phosphor,or amorphous silicon to record the x-ray photos, which are converted into an electrical charge and then converted into a digital image.
 
     CR is often distinguished from DR. CR and DR have many similarities. Both CR and DR use a medium to capturex-rayenergy and both produce a digital image that can be enhanced for soft copy diagnosis or further review. Both CR and DR can also present an image within seconds of exposure. CR generally involves the use of a cassette that houses the imaging plate, similar to traditional film-screen systems, to record the image whereas DR typically captures the image directly onto a flat panel detector without the use of a cassette. Image processing or enhancement can be applied on DR images as well as CR images due to the digital format of each. There are many different types of DR detectors in use in medicine and industry. Each type has its own merits and distinctions and may be applied to certain imaging requirements based on these attributes. 
    CR and DR should not be confused with fluoroscopy, where there is a continuous beam of radiation, and the images appear on the screen like on a TV. This is the system many people are familiar with, where the image of the article being x-rayed is viewed in real time on a monitor or display. Many people think airports use Fluoroscopes for baggage inspection, when in fact LDA's (Linear Diode Arrays) are universally used to generate static images of luggage content. LDA's are also used in a wide variety of other screening and imaging applications, and are also presented in a digital format. Modern fluorosopes use a device called an image intensifier to enhance the analog output of the real time x-ray image, where it is picked up by either a video or CCD camera and digitally enhanced to reduce the noise inherent in the system.