Extraoral Radiography in Pediatric Dental Practice
Extraoral radiography means that both the image detector and the X-ray machine are placed outside the patient’s mouth. The X-ray source and the image detector have to be aligned in order to generate the desired image quality. There are two ways of obtaini
- PDF / 1,876,951 Bytes
- 19 Pages / 439.37 x 666.142 pts Page_size
- 32 Downloads / 269 Views
Extraoral Radiography in Pediatric Dental Practice
Extraoral radiography means that both the image detector and the X-ray machine are placed outside the patient’s mouth. The X-ray source and the image detector have to be aligned in order to generate the desired image quality. There are two ways of obtaining extraoral radiographs: the first way is to work with a stationary X-ray source and image detector and the second is to have the X-ray source and image detector move in synchronicity in opposite directions. The first technique results in a plain radiographic image, while the other technique results in a tomographic image. The latter implies a focal trough, which ideally contains all the tissues one is interested in. More explanation is offered below.
4.1
Panoramic Imaging
The dental panoramic tomography is often called, depending on the region in the world, a panorex, a pan, an OPG, and a DPT, just to name some. They all refer to the same technique and the same image that is generated.
4.1.1 Technique Details The technique implies that the X-ray source and the image detector move synchronously in opposite directions, with the image detector passing as close as possible to the patient’s face. By doing so, one creates a focal trough, or a slice with a particular thickness. The thickness of the slice depends on the width of the X-ray beam. The narrower the beam, the thinner the slice. The latter means a more sharp image, but there is a limit of course. Since the human head is not a sphere, a single pivoting point around which image detector and X-ray source revolve will not provide an optimal image result. Therefore the machines are constructed in such a way that multiple pivoting points are used, which follow the shape of the dental arches as close as possible. The focal © Springer Nature Switzerland AG 2019 J. Aps, Imaging in Pediatric Dental Practice, https://doi.org/10.1007/978-3-030-12354-3_4
31
32
4 Extraoral Radiography in Pediatric Dental Practice
trough of a panoramic image is therefore actually a three-dimensional horseshoe- shape slice through the patient’s head, with the jaws in the focal trough (in focus). Some machines allow for adjustments of that shape, while others don’t. The latter are usually cheaper and assume that one size fits all. It is evident that this is incorrect and that if the shape of the jaw can be followed better, the image will be better as well. The X-ray beam used in panoramic radiography is a vertical narrow slit beam, which can be adjusted (collimated) in height to accommodate for adult or pediatric settings. This collimation is essential when imaging children as it will reduce the radiation burden and avoid unnecessary parts of the head and neck to be exposed. The X-ray beam is also angled slightly upwards (8–12°), which explains why structures in the neck, like for instance a forgotten necklace, will be projected on the patient’s chin in the final image (Fig. 4.1). The fact that the X-rays are angled upwards and are not passing through the patient from the front
Data Loading...
