The Brief Introduction of DR

As the improvement of Medical Standards, Digital radiography is being wildly used in different hospitals from countryside to modern cities. It is applied to the chest, skull, spine and limbs etc from kids to adults.So what is DR? How does it work? And what are its functions?

    What is DR?
    Digital radiography(DR) is a form of X-ray imaging, where digital X-ray sensors are used instead of traditional photographic film. Advantages include time efficiency through bypassing chemical processing and the ability to digitally transfer and enhance images. Also less radiation can be used to produce an image of similar contrast to conventional radiography.

    Digital radiography uses a digital image capture device instead of X-ray film. The gives advantages of immediate image preview and availability; elimination of costly film processing steps; a wider dynamic range, which makes it more forgiving for over- and under-exposure; as well as the ability to apply special image processing techniques that enhance overall display of the image.

    There are two major variants of digital image capture devices: flat panel detectors and high-density line-scan solid state detectors. FPDs are further classified in two main aspects:

    Indirect Flat Panel Detector. Amorphous silicon is the most common material of commercial FPDs. Combining a-Si detectors with a scintillator in the detector's outer layer, which is made from caesium iodide (CsI) or gadolinium oxysulfide (Gd2O2S), converts X-rays to light. Because of this conversion the a-Si detector is considered an indirect imaging device. The light is channeled through the a-Si photodiode layer where it is converted to a digital output signal. The digital signal is then read out by thin film transistors(TFTs) or fiber-coupled CCDs. The image data file is sent to a computer for display.

    Direct Flat Panel Detector. Amorphous selenium FPDs are known as “direct” detectors because X-ray photons are converted directly into charge. The outer layer of the flat panel in this design is typically a high-voltage bias electrode. X-ray photons create electron-hole pairs in a-Se, and the transit of these electrons and holes depends on the potential of the bias voltage charge. As the holes are replaced with electrons, the resultant charge pattern in the selenium layer is read out by a TFT array, active matrix array, electrometer probes or microplasma line addressing.

    A high-density line-scan solid state detector is composed of a photostimulable barium fluorobromide doped with europium or caesium bromide phosphor. The phosphor detector records the X-ray energy during exposure and is scanned by a laser diode to excite the stored energy which is released and read out by a digital image capture array of a CCD.

    Direct digital sensors represent a significant initial investment, but in addition to the convenience of digital images, provide instant images that can reduce the time the patient spends in the dental chair. They also reduce the need for the constant purchase of film and the necessary development chemicals. Early systems used CCD sensor technology, but changed to CMOS sensors following their introduction in early 1998.

    How does it work?
    Indirect digital imaging utilizes a reusable plate in place of the film. After X-ray exposure the plate (sheet) is placed in a special scanner where the latent formed image is retrieved point by point and digitized, using laser light scanning. The digitized images are stored and displayed on the computer screen. This method is halfway between old film-based technology and current direct digital imaging technology. It is similar to the film process because it involves the same image support handling but differs in that the chemical development process is replaced by scanning. This is not much faster than film processing and the resolution and sensitivity performances are contested. PSP has been described as having an advantage of fitting within any pre-existing equipment without modification because it replaces the existing film; however, it includes extra costs for the scanner and replacement of scratched plates.