The digital volume tomography, abbreviated DVT, is a tomography procedure that uses X-rays to produce three-dimensional images of the mouth, jaw and face area. The main area of application is dentistry. It is also used in oral and maxillofacial surgery and in nose and throat medicine.
What is digital volume tomography?
An X-ray tube and a digital image sensor opposite it rotate around the standing, sitting or lying patient. This image sensor is provided with a scintillator layer that is sensitive to X-rays.
The X-ray tube sends out a pulsed, conical X-ray beam that penetrates the examination area and generates a gray-scale X-ray image as a 2D parallel projection. The objects that are outside the focal plane are shown increasingly blurred with increasing distance. Numerous two-dimensional individual images are recorded during a circuit around the observation area.
Depending on the device used, 200 to 600 images are created. These individual images are then put together to form a 2D panorama image that offers a 360 ° representation. Subsequent processing of the images using mathematical methods can reduce the noise and set the desired depth of field.
In order to create a volume graphic from these 2D images, further mathematical processing on the computer is required, in which the gray value images are projected onto the three spatial levels. The result is a volume graphic, the smallest element of which is the mostly cube-shaped voxel.
This volume can be divided into mutually perpendicular planes. This creates axial, sagittal and coronal views of the study area. An axial view allows you to look into the area from above or below, the sagittal view offers a view from the side and the coronal view allows you to look into the area from the front. These views can also be displayed in different colors. Whether this has any diagnostic value is controversial.
Function, effect & goals
The largest area of application of digital volume tomography is dentistry. Here it is often used to plan implants. With their help, the bone volume available for the implants can be determined and foci of disease and pathological changes in the implantation area can be excluded.
The examination of the maxillary sinuses before a planned implantation is also possible with the help of digital volume tomography. In the maxillary sinus, changes in the maxillary sinus and the mucous membrane lining it are searched for. In the lower jaw, it is particularly helpful to depict the mandibular canal. Digital volume tomography is also used in oral surgery to plan operations. With their help, root fractures, injuries to the temporomandibular joints and jaw fractures can be correctly identified. In orthodontics, it is used to identify misaligned teeth and their causes. This procedure is also very useful in preparation for the removal of dislocated or non-erupted teeth.
Another application is the planning of root canal fillings, which are made much easier by the three-dimensional representation. The exact representation of the anatomical relationships and the neighboring structures can protect the maxillary sinus floor, nasal floor, nerves, soft tissues and neighboring teeth. With the help of this procedure, caries centers as well as diseases of the gums and the jaw-holding apparatus can be precisely localized.
It is also used to detect bone defects caused by chronic inflammation, tumors or cysts. Digital volume tomography is also being used more and more in ear, nose and throat medicine. With their help, sinus infections that originate in the teeth can be distinguished from those that are caused by the nasal mucosa. Outside of the medical field, the procedure is used in material testing. There, however, with higher radiation doses.
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At the moment, digital volume tomography is only available for examinations in the head area. When using them, the patient is exposed to X-rays. Therefore, an existing pregnancy should be ruled out beforehand.
However, the exposure to x-rays in digital volume tomography is much lower than in 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 radiation exposure between 500 and 1,500 μS. For comparison: on a flight from Frankfurt to New York, the passenger is exposed to radiation of approx. 90 μS and humans in Germany are exposed to an average annual radiation dose of 4,000 μS due to natural and man-made radiation from the environment.
When using digital volume tomography, it should be noted that metallic objects, e.g. B. Tooth seals that can affect image quality. They absorb all or part of the X-ray beam. This leads to shading of the areas behind and can thus cause phantom objects in the images. In addition, it should be noted that soft tissue is only displayed with little contrast due to ionizing radiation, such as X-rays. Digital volume tomography is much more comfortable for the patient than a CT examination. He does not have to go to 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 only takes 10 minutes. For the doctor, the method offers the additional advantage that the associated planning software enables the operation to be simulated. 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 who wants to use this procedure must provide evidence of the relevant expertise.
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