8_Dental_Radiography

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Student’s Laboratory, Department of Biophysics V. Detailed instruction Exercise preparation. Set up a new folder on your private network drive (U). All files created during the exercise should be saved in this folder. Any files saved at different locations, will be deleted. Setting optimal time of exposition of the radiographic films. Properties of the radiographic film may be defined by using the sensitometer scale (dependence of the blackening of the film upon the exposition). Radiogram with the sensitometer scale for this lab was done in such a way: rectangle 1 (lightest) on the scale was irradiated with X-ray produced by the lamp with anode voltage 30 kVp, anode current 3 μA and the time of exposition 1s. Every next rectangle was irradiated using twice larger exposition (3, 6, 12, 24…and so on, in μAs). Turn on scanner Agfa SnapScan 1236u and apply program Scan Wise (see Section VI) for scanning one of the sensitometer scales. Apply resolution 300 dpi. Save file in BMP format in your folder. Use Pomiary program (see Section IX) to measure an average value of the grey-scale level in each of 21 rectangular areas of the sensitometer scale. Write the measured gray levels in the table. In Statistica program create the graph of the grey level dependence on exposition (apply the logarithm scale for exposition). Interpret the graph course. Decide which exposition should be most accurate to achieve the best contrast for recognizing differences in absorption (extinction) of radiation by the different regions of irradiated object. Taking under attention the fact, that the dentist's rtg plate (film) has the similar properties to the plate with sensitometer scale, count the optimal exposition as well as the optimal time of exposition for anodal current equal to 100 μA. These parameters you will apply for settlement of proper exposition times during collection of the tooth’s radiograms. Collection of radiographic pictures of tooth. Radiograms are prepared with laboratory X-ray lamp XR-100 powered with Eclipse II power supply (see Section VII). A special radiographic film SD-SPEEDX EXPOSURE CHART (see Section VIII) is applied. Place the box with a tooth in the openable chamber in column with the X-ray lamp. Since radiation is created by the laboratory XR-lamp in form of a narrow cylinder (about 2 cm of diameter), the tooth has to be located exactly in centre of the chamber. Turn on the power unit of the lamp and set the anodal current equal to 100 μA. Four radiograms have to be done using the different settings of anodal voltage and different times of exposition (emission of radiation must be turn on and off manually; check time of exposition with your clock or stopper): (1) anodal voltage equal to 30 kVp; time of exposition equal to calculated earlier optimal time of exposition; (2) anodal voltage equal to 30 kVp; time of exposition half of the calculated earlier Dental Radiography 2
Student’s Laboratory, Department of Biophysics optimal time of exposition; (3) anodal voltage equal to 20 kVp; time of exposition equal to calculated earlier optimal time of exposition; (4) anodal voltage equal to 20 kVp; time of exposition twice than calculated earlier optimal time of exposition. Before irradiating films you should inform the assistant about all calculated parameters of exposition. After performing the all expositions, films should be developed according to the instruction (see Section VIII) and rinsed (the least by two minutes) in current cold water. Then leave radiograms to full drying. Dried films should be scanned (see Section VI), the best with resolution of 600 dpi, and record on disc of your team. The examples of test radiograms are presented in the Fig. V. 1. Fig. V. 1. Example radiograms of tooth made with laboratory X-ray lamp for three different settings of exposition parameters (voltages and times of exposition). There are marked possible regions chosen for contrast determination. Analysis of all digital radiograms. In this part make the quantitative analysis of radiograms quality and check finally if the calculated parameters of exposition were chosen optimally. The quantitative analysis will be conducted by enumeration and comparison of the contrasts on all digital radiograms of the tooth. To establish differences in contrast of particular radiograms (Fig. V. 1.) we have to measure the average degree of the grey-scale level of the chosen darker region of the tooth in the picture (ID), the average degree of the grey-scale level of different, lighter region (background) of the tooth (IB) and calculate contrast (K) using equation [1]: I B I D K I [1] Measurements should be done for all radiograms always in the same areas of the tooth; the sizes of analysed surfaces should also be similar (e.g. 40 x 40 pixels). For execution measurements of the grey-scale levels use the Pomiary program (see Section IX). Make the report on the basis of the Radiography template. You can access the template on T: drive. Follow instruction in the template to prepare the Report. Dental Radiography 3 B IB ID
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