Digital radiography 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 (DR) or (DX) is essentially filmless X-ray image capture. In place of X-ray film, a digital image capture device is used to record the X-ray image and make it available as a digital file that can be presented for interpretation and saved as part of the patient’s medical record. The advantages of DR over film include immediate image preview and availability, 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. The largest motivator for healthcare facilities to adopt DR is its potential to reduce costs associated with processing, managing and storing films. Typically there are two variants of digital image capture devices. These devices include Flat Panel detectors (FPDs), and High Density Line Scan Solid State detectors.
FPDs are classified in two main categories:
1. Indirect FPD's - Amorphous silicon (a-Si) is the most frequent type of FPD sold in the medical imaging industry today. Combining a-Si detectors with a scintillator in the detector’s outer layer, which is made from Cesium Iodide (CsI), or Gadolinium Oxysulfide (Gd2O2S), converts X-ray to light. Because the X-ray energy is converted to light, the a-Si detector is considered an indirect image capture technology. The light is then 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 (TFT’s) or by fiber coupled Charged Couple Devices (CCD’s). The image data file is sent to a computer for display where the X-ray technologist can determine whether the image is appropriate for the intended anatomy. Once the Technologist determines the image is appropriate it can be sent to the radiologist’s workstation or printed on film for interpretation.
2. Direct FPD's - Amorphous Selenium Flat Panel Detectors (a-Se) are known as “direct” detectors because X-ray photons are converted directly to charge. The outer layer of the flat panel in this design is typically a high voltage bias electrode. The bias electrode accelerates the captured energy from an X-ray exposure through the amorphous selenium layer. X-ray photons flowing through the selenium layer create electron hole pairs. These electron holes transit through the selenium based on the potential of the bias voltage charge. As the electron 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. The image data file is sent to a computer for display where the X-ray technologist can review the image and check positioning and if desired, transmit the image to the radiologist’s workstation for diagnosis.
A High Density Line Scan Solid State detector device is composed of a Photostimulable Barium Fluoro Bromide doped with Europium (BaFlBr:Eu) or Cesium Bromide (CsBr) phosphor. The phosphor detector records the X-ray energy during exposure and is scanned by a linear laser diode to excite the stored energy which is released and read out by a digital image capture array of Charge Coupled Devices (CCD’s). The image data file is transmitted to the X-ray technologist at a computer for review and then sent to the radiologist for further interpretation.