EXTRA ORAL RADIOGRAPHS

today's discussion is about advanced radiographic techniques the first one is auto paint tomography also contest panoramic image ok I'll be covering just the basic mechanisms to do these videos see in orthopedic Rafi as we can see in the image first on the right side you can see there is a tube head that is the x-ray source on the left side of the oh there is a receptor with secondary collimator okay the blue part the entire thing is the receptor with a localized collimator that is the gray box okay now both of these things are moving okay first we can see the tube head is the direction of x-ray source around the patient and in the similar direction the receptor is also moving in this diagram in the anti clockwise direction okay so see in this picture the first picture first one is the position of the tube head at this time okay and I hope everybody can see the black tea bag with the number one written on it and the image is formed on the receptor on the opposite side okay here with the arrows we can see the starting point is number one the image is form just opposite to it then again the tube head and the receptor Cassatt the receptor is also moving okay so now the tube has the head comes to position two then position three then in this next diagram position four five and six in this way it is completing that entire rotation okay and simultaneously at the same time the image is formed see on the image on the right side first a partial the most posterior part of the right left side is formed then a little bit more a more from position three than from position four five six and entire image is formed in six steps here for for the ease of understanding only six steps are shown but actually there are very millimeter steps when actually the she moves it's continuous in multiple steps not only six steps okay so in also in this the previous picture salt only you can see that the tube is never going to the most anterior part okay it is moving in the like the most interior or midline interior part it is not covered by the tube and at the same time the receptor never goes to the most posterior right okay it has a significance we'll see further now in this diagram we can see that in between there is a center of rotation okay the center of rotation is the black dotted line in the center which is a continuous center of rotation when tube head moves as shows the center of rotation also shifts continuously and follows this arc okay so here comes the real image really there are three types of images are formed real images double images and ghost images okay first one this is the real image it is formed between a real image is formed of the objects which are placed between receptor and center of rotation okay since the receptor never comes to the most posterior part the most posterior part is left okay next is the ghost image it is formed of the objects which are between source and center of rotation so the source that is the qubit is never going to the N most anterior part so anterior participate okay it is between center of rotation and source the ghost image now comes the double image it is formed between the objects which are posterior to the center of rotation and have the image twiced okay so it comes in this diamond shape of area only these objects will be imaged double and that posterior to the center of rotation coming to computed tomography and cone beam computed tomography this is the picture showing computed tomography in which Delta x-ray source and if fan-shaped beam of x-rays is coming and falling on the detector so x-ray source is the leg is like the tube ID from their x-rays coming and detectors are the receptors or the detectors which detect the x-ray which is coming out of the patient okay so after activation the x-rays will fall on that detector okay this picture shows that prejean third generation first a diagram is the third generation how earlier CT machines were in that the tube head is moving in the same way detectors is also moving because there are not a complete circle of detectors only an arc of detectors so it is also moving then B diagram B shows the fourth generation of city in which detectors are a complete circle so detectors doesn't have to move every place has a detector only that the overhead is moving okay then can see this is the fifth generation which is mostly used now here the patient is moving inside the gantry see the big black arrows is showing the movement of the patient at the same time x-ray source and detectors everything is moving the detectors are also moving within the gantry an x-ray source is also moving within the gantry and the image form each slice is imaged so each slice is stored in the form of pixel this cross diagram we can see has 512 by 512 pixels in more advanced machines this is double of this that is 1024 pixels by 1024 pixels this each square is called a pixel when we assess the volume also okay that is the third dimension of this each square it becomes a box and each of this square each pixel has been given a Hounsfield unit okay meets each pixel will have a grey skills based on the animation okay so bone has more activation means less of the x-rays will pass through it less or none actually will pass through bone so the Hounsfield unit will be high that is from 400 to 1000 and for air every all the x-rays will pass through air nothing will be attenuated or very less will be activated so for air CT number or household number is very less that is - thousand