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- 1. Alfarabi college .. Radiology .. Level 7 Group one Dr . Islam kassem Digital X ray Level 7 Group one 20091109 200911027 200911354 200911634
- 2. Introduction The second phosphor based approach is a stimulable phosphor system, in which the phosphor contains traps for electronsFor decades now, unlike any major excited by incident x-rays. The latent imagemedical imaging methods such as formed by the trapped electrons is thenultrasound, nuclear medicine etc, all of brought out, in the form of a blue-lightwhich are digital, conventional x-ray image, by illuminating the phosphor, pointimaging remains a largely analog to point, with a red laser. Unlike thetechnology. intensifier system, the stimulable phosphor system cannot produce instant images, for the cassette must be carried to a laser scanner for readout by a photo-multiplier,Why digital? which performs the digitization. The third commercial digital system is based on using an amorphous seleniumMaking the transition from analog to photoconductive layer to convert x-raydigital could bring several advantages to x- photons directly to charge carriers. It usesray imaging. These would include an amorphous selenium photoconductorimprovement in contrast and other aspects sensitized by depositing charges on itsof image quality by means of image surface by a corona discharge, as inprocessing: radiological images could be xerography. After exposure to x-rays, thecompared more with those obtained from image resides as a charge distribution onother imaging modalities, electronic the a-Se surface, which is read outdistribution of images within hospitals electronically and then digitized. With thecould make remote access and archiving use of flat panel detectors in the a-Sepossible, highly qualified personnel could method the x-ray image is captured and isservice remote or poorly populated regions converted directly to a digital signal forfrom a central facility by means of display, processing, and storage. Even a"teleradiology"; and radiologists could use higher resolution can be achieved due tocomputers more effectively to help with the use of these flat panel detectors in the a-diagnosis. Se method.Digital radiography is currently practiced through the use of three commercialapproaches, two of which also depend on phosphor screens. The first phosphorbased approach is to digitize the signal from a video camera that is optically coupledto an x-ray image intensifier to provide an instant readout
- 3. The use of X-ray image receptors that produce a digital image is becoming increasingly important. Possible benefits include improved dynamic range and detective quantum efficiency, improved detectability for objects of low intrinsic contrast, andreduced radiation dose. The image can be available quickly. The displayis separated from the image capture so that processing and contrast adjustment are possible before the image is viewed. The availability of a digital image means ready input into PACS and opens up the possibility of computer-aided detection and classification of abnormality. Possible drawbacks of digital systems include high cost, limited high contrast resolution and the fact that their clinical value is sometimes not proven in comparison with conventional, analogue techniques. The high contrast resolution attainable with such systems is discussed and the problem of sampling limitations and aliasing considered. The properties and limitations of digital systems using computed radiography, caesium iodide plus CCDs and active matrix arrays with either caesium iodide or seleniumdetectors are demonstrated. Examples are given of digital systems for mammography and general radiography and their performance is demonstrated in terms of clinical assessment and measurements of the modulation transfer function and detective quantum efficiency. Digital radiography It 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. 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.
- 4. Dental radiographs :Provide essential information about oral health. They are an important partof a patients dental record. Some dental offices now use computers to helpcapture, store and transmit dental radiographs. Dental radiographs producedwith a special computer create digital images (computerized dentalradiographs) that can be displayed and enhanced on the computer monitor.When the digital radiograph is exposed, the image is transmitted to acomputer processor(with or without a cable) or, in the case of an imagingplate, the clinician removes the plate from the mouth and scans it with aspecial reader, similar to a compact disc player. Unlike conventional filmthat may take between three and five minutes to process, a digitalradiographic image generally can be viewed quickly on the computer screen.The image is displayed in a large format on the screen, in comparison withthe small films that are viewed on a light box.The clinician can use magnification to enhance specific problem areas of atooth, as well as alter brightness and contrast in the image. Viewing anenhanced dental radiograph on a computer screen can help a dentist bettersee a problem area.Digital X-Ray Machine and Camera SystemParts of a Digital X-Ray Machine:The digital X-Ray machine consists of an X-Ray tube and driver to source X-Ray. TheX-Ray passes through the patients body and the digital camera (located on the otherside of the patient) captures the resulting image. The main base station controls theX-Ray tube, analyzes the image and displays the image on the CRT.Digital Camera:The digital camera converts the received image into digital signal and transfers thedigitized image to the base station through a fiber optic link.
- 5. Main Base StationThe functions of the main base station are as follows: Drive and control the X-Ray tube Communicate with the digital camera system through Fiber Store the pictures on the hard disk for image retrieval and processing Interface to an operator console for overall system control and image manipulation Analyze and enhance the image stored on the hard disk and display the enhanced X-Ray image on a CRT monitorPrinciples :Conventional imagingConventional intra-oral radiographic film consists of silver halidegrains in a gelatine matrix. When this film is exposed to X-rayphotons the silver halide crystals are sensitized and are reduced toblack during the developing process. The film acts as both theradiation detector and the image display.With extra-oral films indirect action receptors are used to helprecord the image. This type of film is sensitive to light photonswhich are emitted by adjacent intensifying screens. Although thefilm is constructed of silver halide crystals these are primarilysensitive to light rather than X-rays. The use of intensifyingscreens reduces the dose and can be used where fine detail is notrequired.Digital imagingIn digital radiography, instead of the silver halide grain the imageis constructed using pixels or small light sensitive elements. Thesepixels can be a range of shades of grey depending on the exposure,and are arranged in grids and rows on the sensor, unlike therandom distribution of the crystals in standard film. However,
- 6. unlike film the sensors are only the radiation detector and theimage is displayed on a monitor.The signal that is produced by the sensor is an analogue signal, i.e.a voltage that varies as a function of time. The sensor is connectedto the computer and the signal is sampled at regular intervals. Theoutput of each pixel is quantified and converted to numbers by aframe grabber within the computer. The range of numbers isnormally from 0 to 256 with 0 representing black, 256 representingwhite and all others are shades
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