The prototype receptor (the recording medium) most commonly used in dental radiography is the radiographic film. However, there are many other new more efficient receptors than the formed one that can be used in radiography such as Digital image receptors. Problems related to film radiography: 1) Processing The long exhaustive chemical processing steps needed for film radiography, for example immersing the film in the developer or the fixer in specific concentrations at specific temperature. 2) Geometry One of the problems of dental radiography is having different dimensions than normal. I.e. having a longer tooth, or a shorter one or some parts of the tooth are not appearing in the image. 3) Dose issues One of the main problems with the traditional film radiography is that in some cases you need to concentrate or increase the dose of the radio used to capture a clear readable image. It has been proved by so many researches that the higher the dose is, the more side effect it would have on a human body. 4) the most significant faced problem in radiography is interpretation. Interpretation of radiographs is to describe the radiograph and to know each color symbolizes which condition. Note that digital radiography and film radiography give equal image quality. 1
- Digital Radiography Advantages 1) Processing Nowadays, digital imaging eliminates the detrimental effects of inadequate film processing on diagnostic quality and the difficulty of maintaining high quality chemical processing since chemicals are not used in digital radiography. 2) Geometry Unfortunately though, geometry remains a major problem in digital radiography as it depends on the patient s mouth and the radiographer. 3) Dose Digital imaging succeeds in reducing the dose since some digital image receptors are more sensitive than the habitual radiographic films. - The more sensitive the receptor is the less the exposure time and the faster the technique will be. 4) Accuracy and Readability In addition to eliminating the interpretation problem by being able to edit or zoom on some defects in the image after it is ready. So we can change contrast, brightness and the quality of the image after it is taken. It s a very fast technique I.e. In charge coupled technique (CCD) the image is taken spontaneously by pressing the responsible button after placing the appropriate receptor inside the patient s mouth. 5) Record keeping and patient history records For both techniques, we have to store the patient s information and case related history including previous radiographs. Keeping a record for a film is a very hard process since it requires many hard accurate steps. While storing a small file requires fewer efforts. Moreover, patients appreciate the advancing dentists; having a clinic with developed new techniques convinces the patient more. Thus digital imaging helps in dental marketing. 2
- Digital Radiography Disadvantages Even though, there are lots of advantages for digital radiography, it does have some disadvantages in comparison to the film option. The initial expense of setting up a digital imaging system is relatively high; 1. Initial Set up cost We have to keep in mind though, that the maintenance of digital radiography is cheaper than the manual radiographic technique. The Radiographic film is used one time unlike the digital image receptors which are reusable. 2. People adoption and trust As the case with any new technology, some people don t trust this equipment due to either lack of information or fear of change. 3. Variety of options to choose from Another problem is the large number of digital receptor types found, so it s somehow confusing to decide which one to use. While some people consider this as a disadvantage, it could be considered as an advantage as of the competition and varieties of products, costs are dropping down dramatically. In contrast to the wide variety of products in the digital option, we have only two major types of radiographic films. - Concept and Technology Involved High quality computer to visualize the radiograph, receptor with different sizes, internal and external storage are needed for digital imaging to be performed. Digital image receptors are found in the same typical sizes as the radiographic film; small sizes for the intraoral use, bigger sizes for skull radiography. The idea of digital imaging is the same photo process as a computer monitor or a camera screen. The digital image is made up of a large number of discrete picture elements called (pixels). Their size is so small that the image appears smooth at normal magnification. 3
The location of each pixel is uniquely identified by a row and column coordinate within the image matrix.the value assigned to a pixel represents the intensity (grey level) of the image at the location. On other words the image is formed of small units (numbers) each unit alone has no value.but if you put them all together like in a mosaic an image will be formed. If you enlarge a radiographic periapical image, small squares with different colors appear (white, grey, and black) Range of numbers is (0-255) accordingly there are 256 different choices. Number 0 corresponds to the black color while number 255 corresponds to the white one. Keep in mind that the black color in the radiographic film has a higher number due to the large number of photons needed to reach the film. The resolution of the image Depends mainly on how this range (0-255) is fractionated. This is called bit depth or grey scale. Bit depth describes the potential accuracy of a particular piece of hardware or software that processes audio data. In general, the more bits that are available, the more accurate the resulting output from the data being processed. Hence, 8 bits will give better quality than 3 bits. Example, there will be 2^8 grey color levels in the 8 bits image while 2^3 levels will be found in the 3 bits image. Another example, if there are 256 color options the mineralized enamel can be distinguished from the demineralized enamel. If there are only 8 color options you there will be no difference between layers of the tooth. The more color options the image has the more difference will be between tissues. The upcoming part of the lecture covers two types of digital receptors; solid state receptors and photostimulable phosphor plates (PSP) The main difference is that solid state receptors have a direct image access while PSP plates require laser processing accordingly it s indirect and it s slower. 4
- Solid State Receptors There are two subcategories of solid state receptors: - Charge-Coupled Device (CCD) - Complementary Metal-Oxide Semiconductor technology (CMOS) Solid state receptors are found in most clinics. Solid state receptors are thicker than photostimulable phosphor receptors. Image access is direct without the need for laser scanning or chemical processing The Wired solid state receptor is linked to a cable plugged into a computer, while the wireless one is attached to a transmitter without a cable. How to take a radiograph for the patient using this technique? By positioning the receptor inside the patient s mouth and pressing the proper button, you can visualize the image on the computer s screen. Concept of imaging through these receptors: Energy transfer between photons and the receptor, thus electrons move into more active bands, these electrons (electrical current) will be conducted through transistors to be visualized directly as an image - Photostimulable Phosphor The shape of PSP plate is similar to the radiographic film but instead of immersing it in chemicals it is placed in a laser reader that is linked to a computer. Similar to the film, PSP plate is formed by base and coating layers. The only difference is in the active layer. The PSP active component used for radiographic imaging is europium-doped barium fluorohalide. While the one used in the radiographic film is silver halides. How does an image form? The active component has a certain structure, when it s exposed to energy this structure will change forming a latent image and to visualize the image the image is processed either by a laser reader as in PSP receptors or by chemical processing as in radiographic film. 5
In other words, when europium-doped is exposed to photons its ionic state will change from +2 into +3 (losing one electron) increasing its energy state this is called latent energy. The lost electron must receive light energy (laser) to return back into its original place to give energy in the form of light. This Light will be analyzed into numbers that correspond to certain gray value forming a radiographic image. To summarize - Energy transfer between photons and europium-doped receptor - Forming an electron in an activated state - Formation of a latent image - To visualize the latent image, it s processed by a laser beam - Forming energy in the form of light - The real image is formed by calculating the energy difference by a tool called photomultiplier The image is taken, we laser scan it and then we erase it because laser has small energy that is not enough to move all activated electrons out of their places. Otherwise the two images will be superimposed one image over the other. Some scanners erase the taken images automatically after they are taken Another erasure technique by using the viewing box which is used to view films, you design a box and by using a glass slice and directing the active side of the receptor against the light, thus the image will be erased. The key clinical feature of these detectors is the rapid availability of the image after exposure. The matrix and its associated readout and amplifying electronics of intraoral detectors are enclosed within a plastic housing to protect them from the oral environment. In plain English, The main advantage of these receptors that they are reusable ones; they are placed in metallic sleeves before taking the radiograph to prevent the occurrence of penetration. Before taking a radiograph for the next patient the sleeve is changed and the receptor is sent to be sterilized. Patients prefer this type of receptors because they are thin, flexible and convenient similar to the radiographic film. Therefore the holder of radiographic films can be used with this type of receptors. 6
Photostimulable phosphor receptor is the best choice for dental students and large offices because it doesn t break easily moreover it s cheap in comparison with solid state receptors which is most commonly used in implants, endodontic and small practices The main disadvantage as mentioned before that it s indirect and consumes more time. What are the main factors to determine receptor of choice? Image quality, dose and cost For example if receptor X gives quality slightly higher than receptor Y while receptor X is much more expensive than receptor Y, definitely we ll go for receptor Y. Image quality given by a receptor must be enough to perform a diagnostic task; the ability to recognize caries, apical diseases and horizontal bone loss. In general there is no difference in the diagnostics between CCD and PSP if used properly. Prepared by Mays Mohmd Nasser If there is any question don t hesitate to notify me Email: mays-nasser@hotmail.com 7