ORAL RADIOLOGY - II LECTURE 5 PANORAMIC RADIOGRAPHY Panoramic radiography is an extra oral radiographic procedure that produces a single image of the facial structures that include maxillary and mandibular arches with their supporting structures. Historically, the concept of obtaining dental arches on a single film was developed independently by Dr. Numata and Dr. Paatero. Principles of panoramic radiography In the panoramic x-ray machine, the receptor or film is attached to a rotating system and moves in the same direction as the beam from the x-ray tube. This movement of x-ray source and the receptor around the patient’s head creates a curved focal trough - a zone in which the objects are displayed clearly on the resulting radiograph.  The rate of movement of the receptor is regulated to be the same as that of the x-ray beam sweeping through the dentoalveolar structures on the side of the patient nearest the receptor.  A slit shaped lead collimator is used on the x-ray tube and reduces the size of the beam and is hence known as slit-beam/pencil beam or narrow beam. Another collimator between the object and the film further reduces the scattered radiation from the object to the film.  Structures on the opposite side of the patient (near the x-ray tube) are distorted and appear out of focus.  Structures near the x-ray source are so magnified that they are not seen as discrete images on the resultant image.  Because of both of these circumstances, only structures near the receptor are captured on the resultant image. Focal trough Focal trough is a three-dimensional curved zone or image layer, where the structures within this zone are reasonably well defined on the final panoramic image. In image shown, the focal trough is an imaginary zone passing through the midline of the mandibular dental arch and body of the mandible Focal trough depends upon: • Brand of equipment used and with the imaging protocol selected within each unit. • Path and velocity of the receptor and x-ray tube head, alignment of the x-ray beam, and collimator width. As demonstrated in the image A above shows xray tube head moving from 1 to 3 rotating about a center of rotation on right side while taking radiograph of the left jaw. A it completes its rotation from 1 to 3, half of the jaw or the entire left side of the jaw is radiographed. The computer screen shows image development corresponding to the movement xray tube head makes from 1 to 3. Types of images formed • Real Image – Focal trough – objects situated between center of rotation and receptor/film. • Double image – region posterior to the center of rotation where the structures are intercepted by x-ray beam twice • Ghost image – objects situated between the center of rotation and x-ray source.

Oral Radiology

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