Cone beam computed tomography

The digital volume tomography ( DVT) is a three-dimensional imaging tomography method with the use of X-rays, which is used mainly in the ear, nose and throat medicine, oral and maxillo- facial surgery and dentistry. In dentistry, we are now seeing from the dentals volume tomography. In English-speaking is common for this procedure, the term cone-beam CT ( CBCT ).

Imaging

Similar to the computer tomography or magnetic resonance imaging is used, the DVT the generation of sectional images. As with the X-ray digital DVT also rotates in an X-ray tube and an opposite digital image sensor, a so-called flat panel detector, the X-ray sensitive scintillator has a layer of a lying, sitting or standing patient. The 180 to 360 degrees rotating X-ray tube emits a cone-shaped, usually pulsed X-ray ( X-ray flash ). The X-ray radiation penetrates the three -dimensional study area and produced an attenuated gray values ​​of X-ray image as a 2D parallel projection. The entire rotating assembly is conducted in such that the center is always exactly in the desired viewing level. Here are movement -related objects outside this focal plane increasingly blurred. Thus, it is possible to simultaneously see through both halves through the skull and only one of them depict sharp.

During the revolution of the x-ray tube, a large number of two-dimensional frames is taken, the width of the image in the direction of the circulation is usually very limited in the panoramic image. Often come here one-dimensional line sensors or narrow two-dimensional image sensors. Due to the circular circumferentially scored roughly series of images creates a fluent observable 2D panoramic image. With a subsequent mathematical clearing using a PC can be created by scaling, matching and brightness correction of the images an optimized panoramic image with the same pixel can be superimposed from different images to reduce noise and adjust the depth of field.

As a further step leading can be generated in the three spatial levels with correspondingly more sophisticated computational methods beyond a gray-scale image coordinates. This three-dimensional coordinate model corresponds to a volume graph, which is composed of individual voxels. For this photo series are needed, each with wide 2-dimensional images, which show all possible projections of the 3D space in the respective 2D plane on the sensor. For this volume later, individual slices ( tomograms ) can be generated in any spatial planes and 3D views of the body.

By incurred for imaging orbital periods of up to 30 seconds sometimes arise camera shake that can affect the quality of the imaging is negative, since they can not be at the algorithmic processing completely eliminate mathematically. Metallic objects such as dental fillings can also produce unwanted picture noise, since they partly to fully absorb the beam and behind shade -lying areas, which can lead to phantom objects.

Comparison with other radiological imaging techniques

Data collection and calculation of the image data of the digital volume tomography was most similar to the rotational angiography. To capture the raw data here comes the image intensifier of an angiography system, or a C-arm used.

A DVT generated for the calculation of three-dimensional structures of two-dimensional images as data set, while the imaging of a computer tomograph was initially based on a one-dimensional detector on a single-line detector. The difference, however, today increasingly blurred, as current CT scanners up to (2 × ) have 320 lines and therefore also work with a two-dimensional projection, ie with a cone beam and not with a fan beam.

Regarding the radiation exposure is the DVT with effective doses between 0.1 mSv and 0.6 mSv for the majority of devices in the field of a modern spiral CTs. However, by means of DVTs no imaging below the head possible, so that the DVT limited to the use in dentistry, oral and maxillo -facial surgery, and ear, nose and throat medicine (paranasal sinuses, middle ear, and TMJ ) is. But here arises a wide range of application of the DVT.

Under the current Regulation X of the operation of such a device (as opposed to a CT ) allowed in a dental office by the dentist if he has a correspondingly expanded qualification according to X-ray Ordinance and expertise Directive in Germany. The same applies to the ear, nose and throat doctors.

The first devices for an application of digital volume tomography as a substitute for a conventional CT are already in development and will be used for some time in addition to increasing clinics in numerous private practices routinely.

Areas of application

The DVT was in dentistry mainly used for planning of operations and the placement of implants .. Meanwhile, they also in traumatology, oral and maxillofacial surgery, endodontics ( root canals ), TMJ treatment and periodontics (gum treatment ) were used. Thus, for example, the exact location of complicated relationships impacted ( wisdom ) teeth, about the mandibular canal or the maxillary sinus can be accurately determined. In dental surgery, DVT is mainly used for the diagnosis of bony, dento - maxillo - facial structures. Possible indications are bony alveolar process and pathological changes such as odontogenic tumors and larger periapical lesions.

In otolaryngology it is also used for diagnosis and before surgery of the nose or sinuses of the skull base. Using DVT can also be distinguished between odontogenic sinusitis ( herkommenden from the tooth sinus infection ) and sinusitis rhinogenic ( herkommende of the nasal mucosa inflammation of the sinuses ).

The case at the center of the viewing stand antrum thus forms the interface between dentistry and ear, nose and throat medicine

Appliances and software, dental Volumentomografen

Meanwhile, more and more large dental companies have relocated to the manufacture or distribution of dental Volumentomografen. Due to the declining cost of DVT these devices have become interesting for general dental practices. In particular, so-called combination devices with additional sensors ( for panoramic radiograph and lateral cephalogram ) lend themselves to a general - dental dental practice. Currently, there is also a trend towards devices with freely adjustable volume specific fields of inquiry (Field of View = field of view) for further dose reduction is emerging. The data formats are standardized, more and more, but not all manufacturers provide the DICOM standard for archiving and sharing of digital tomography between doctors ready. Partial completely vendor-specific file formats are chosen so that the unimpeded exchange between doctors is difficult. There are a few devices that have been developed specifically for the requirements in the ENT area. These devices represent next to the DVT and the classic 2D projection radiography are available which have your eligibility for simple questions, such as a nasal bone fracture. Devices with a 2D projection radiography are part of radiological qualifications of the ENT specialist, which currently can not be conveyed with pure DVT devices.

DVT devices in the ear, nose and throat medicine

In the Ear, Nose and Throat have DVT devices, also due to the much smaller number of doctors working in this field, not so often found its way into the diagnostics. The necessary in this area DVT devices must necessarily depict large volume and are therefore much more expensive than many dental Volumentomografen.

Other areas of application

Away from the medical technology, the process is used in a slightly modified form also for material testing. This larger sensors with alteration of sensitivity, longer exposure time and higher X-ray doses (higher voltage of the X-ray tube ) are used.