- Digital Fluoroscopy
- Digital Plain Film Radiography
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.
Instead of X-ray film, digital radiography uses a digital image capture device. This 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 (FPDs) and high-density line-scan solid state detectors.
Flat Panel Detectors (FPDs)
FPDs are further classified in two main categories:
- Indirect FPDs.Amorphous silicon (a-Si) 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 FPDs. Amorphousselenium (a-Se) 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 micro plasma line addressing.
High-density Line-scan Detectors
A high-density line-scan solid state detector is composed of a photostimulable barium fluorobromide doped with europium (BaFBr:Eu) or caesium bromide (CsBr) 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.
Medical Uses for Digital Radiography (DR) can be broken into two subcategories, Dental, and the rest of the body.
The radiological examinations in dentistry may be classified into intraoral – where the film or sensor is placed in the mouth, the purpose being to focus on a small region of the oral-maxillofacial region and extra oral where the film or sensor is placed outside the mouth aiming to visualize the entire oral maxillofacial region. Extra oral imaging is further divided into orthopantomogram, showing a section, curved following more or less mandible shape, of the whole maxillofacial block and cephalometricanalysis showing a projection, as parallel as possible, of the whole skull.
Digital radiography in dentistry provides the clinician with the ability to store their images on a computer. This provides two key advantages over film in the form of full screen images that can be enhanced and zoomed in on, aiding diagnostics and providing easier patient communication, as well as allowing dental offices to communicate images electronically, allowing for simpler referrals and, where applicable, easier insurance claim submission.
Rest of the Body Digital Radiography
Digital Radiography is replacement of the former Analog methods of detection, with the almost instantaneous development of images on a digital display, instead of the former methods of film and the associated delay in time and chemistry consumption.
Industrial Usage of X-Rays
Aerospace is an industry that has experienced great growth in recent decades. Non Destructive Testing(NDT) in aerospace has a special driver of its own due to the high levels of human traffic involved; the crash of a civil or military airliner has the ability to cause loss of life reaching catastrophic proportions. Therefore, strict NDT specifications have been set to detect very small cracks and defects in engine turbo discs, blades and airframe structures, in both production and ongoing maintenance.
Digital Radiography (DR) has existed in various forms (for example, CCD and amorphous Silicon imagers) in the security X-ray inspection field for over 20 years and is rapidly replacing the use of film for inspection X-rays in the Security and NDT fields. DR has opened a window of opportunity for the aerospace NDT industry due to several key advantages including excellent image quality, high POD, portability, environmental friendliness and immediate imaging.
Digital radiographic systems
Digital dental radiography comes in two forms: direct, that connects directly to the computer via USB and provides immediate images, and indirect (photostimulable phosphor plates or PSP) which uses plates that are radiated and then digitally scanned.
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. Indirect digital imaging (also termed Computed Radiography) 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.