Digital volume tomography, abbreviated DVT, is a tomography procedure that uses X-rays to provide three-dimensional images of the mouth, jaw and face. The main field of application is dentistry. It is also used in oral and maxillofacial surgery and in nasal and ear medicine.
What is digital volume tomography?
Digital volume tomography, abbreviated DVT, is a tomography technique that uses X-rays to provide three-dimensional images of the mouth, jaw and face. An X-ray tube and a digital image sensor opposite it rotate around the standing, sitting or lying patient. This image sensor is coated with a scintillator layer that is sensitive to X-rays. The X-ray tube emits a pulsed, cone-shaped X-ray beam that penetrates the examination area and produces a gray-scale X-ray image as a 2D parallel projection. The objects that lie outside the focal plane are increasingly blurred as the distance increases. During one orbit around the observation area, numerous two-dimensional individual images are acquired. Depending on the instrument used, 200 to 600 images are produced in this way. These individual images are then combined to form a 2D panoramic image that provides a 360° view. Subsequent processing of the images using mathematical methods allows noise to be reduced and the desired depth of field to be set. To create a volume graphic from these 2D images, further mathematical processing is required on the computer, in which the gray-scale images are projected into the three spatial planes. The result is a volume graphic whose smallest element is the usually cube-shaped voxel. This volume can be decomposed by planes perpendicular to each other. This results in axial, sagittal, and coronal views of the area of interest. An axial view allows to look into the area from above or from below, the sagittal view offers a view from the side and the coronal view allows to look into the area from the front. These views can additionally be displayed in different colors. Whether this has diagnostic value is debatable.
Function, effect, and goals
The largest area of application for digital volume tomography is dentistry. Here, it is popular for planning implants. With its help, the bone volume available for the implants can be determined and foci of disease and pathological changes in the implantation area can be ruled out. Digital volume tomography can also be used to examine the maxillary sinuses before a planned implantation. In the maxillary sinus, this involves looking for changes in the maxillary sinus and the mucosa lining it. In the lower jaw, imaging of the mandibular canal is particularly helpful. Digital volume tomography is also used in oral surgery for planning operations. With its help, root fractures, injuries to the temporomandibular joints and jaw fractures can be detected perfectly. In orthodontics, it is used to determine tooth misalignments and their causes. This procedure is also very useful for preparing the removal of displaced or unerupted teeth. Another application is the planning of root canal fillings, which is greatly facilitated by three-dimensional imaging. Accurate visualization of anatomical conditions and neighboring structures allows the maxillary sinus floor, nasal floor, nerves, soft tissues and adjacent teeth to be spared. This procedure can also be used to precisely localize foci of caries as well as diseases of the gums and the jaw support apparatus. It is also used to detect bone defects caused by chronic inflammation, tumors or cysts. Digital volume tomography is also being increasingly used in ear, nose and throat medicine. With its help, sinusitis originating from the teeth can be easily distinguished from sinusitis caused by the nasal mucosa. Outside the medical field, the method is used in materials testing. There, however, with higher radiation doses.
Risks, side effects, and hazards
Currently, digital volume tomography is only available for examinations in the head region. When it is used, the patient is exposed to X-ray radiation.Therefore, an existing pregnancy should be ruled out beforehand. However, the exposure to X-rays with digital volume tomography is much lower than with conventional X-rays or a CT scan. With DVT, the radiation exposure is between 20 and 300 μS, depending on the device used. A CT scan would cause a radiation exposure of between 500 and 1,500 μS. By comparison, a passenger traveling by air from Frankfurt to New York is exposed to radiation of approximately 90 μS, and humans in Germany are exposed to an average annual radiation dose of 4,000 μS from natural and man-made radiation from the environment. When using digital volume tomography, it should be noted that metallic objects, e.g. dental fillings, can influence the image quality. They absorb all or part of the X-ray beam. This leads to shadowing of areas behind them and can thus cause phantom objects on the images. It should also be noted that soft tissue is not very well contrasted by ionizing radiation, such as X-rays. Digital volume tomography is much more convenient for the patient than a CT scan. He does not have to visit a special practice or go into a narrow tube, which is a real problem for some patients. In addition, the results are available very quickly. The examination usually takes only 10 minutes. For the physician, the procedure offers the additional advantage that the associated planning software enables simulation of the operation. This avoids unpleasant surprises during the operation. Good preparation can reduce the duration of the operation and thus the risk of side effects of anesthesia, swelling in the surgical area and infections. Anyone wishing to use this procedure must provide proof of appropriate expertise.
