That's Life: Increase the Beam
That's Life: Increase the Beam
Concerned about the radiation safety? Confused about how Cone Beam Computerized Tomography differs from traditional CT imaging or X-rays? You’re not alone. Here’s the facts.
CBCT vs. X-Ray
Cone Beam Computerized Tomography and conventional X-ray technology use radiation to capture images. When an X-ray tube or X-ray generator is energized, it emits electromagnetic energy wave. Depending upon their wavelength, these energy waves can penetrate some solid objects or may be absorbed by others. To make an X-ray image of human bone or tissue, X-ray pulses are concentrated and aimed at the area of interest to illuminate the structure that has a radiographic film behind it. Dense material such as bone and teeth, which are high in calcium, absorbs photons. Softer tissue allows more of the rays to pass through to the film creating the familiar black and white (grayscale) images we all know. In the case of digitized 3D imaging, the traditional silver X-ray film is replaced with an electronic imaging receptor. Regardless of whether the images are traditional X-ray technology or digitized 3D tomography, there are real health hazards for patients anddental team members. Certain precautions must be taken to avoid unnecessary or excessive exposure to X-ray radiation.
Radiation Health and Safety
There are three types of radiation exposure that can cause health problems for dental professionals. Primary radiation is the focused energy used to create the images captured on film or by a digital imaging receptor. Exposure to primary radiation is acceptable and necessary for generating latent images or volumes of 3D data. When performed properly when absolutely necessary, the risk to patients is minimal and the operator is never exposed.
Secondary radiation is any radiation that is scattered or deflected upon impact,. It travels to all parts of the operatory or scanning suite. This secondary radiation can be contained and controlled with proper equipment maintenance, such as shielding of the patient the X-ray technician. Secondary radiation is weaker than primary radiation, but still represents a health hazard if not properly controlled.
The third safety risk is not a type of radiation, but rather the cumulative effects of radiation exposure. When handled properly, radiation in a dental operatory or scanning suite is not harmful and the diagnostic benefits outweigh the risks for most patients. The most sensitive cells to damage from the cumulative effects are red and white blood cells, bone marrow and thyroid tissue, as well as those of the genitals and embryonic tissue, especially in a pregnancy’s first trimester.
To protect the patient from unnecessary exposure to X-ray radiation, a lead apron with a thyroid collar is frequently utilized for conventional X-rays. However, some shields may interfere with CT scanning equipment and usually cannot be used.
Because of the risk of exposure to secondary radiation and the cumulative effects of repeated exposure, it is important the operator is protected. At the very least, the equipment operator should stay six to eight feet from the X-ray tube, preferably behind a barrier such as an operatory wall or, if possible, a wall shielded with lead barriers or leaded glass.
To measure how much radiation an Xray technician is exposed to, employees are issued dosimeters. These devices are technician specific and must be worn at all times. Radiation dosimeters measure the cumulative doses of ionic radiation and are monitored regularly to make sure exposure limits remain at safe levels.
Computed Tomography
In traditional X-rays, a single slice of structure is imaged on film, but other layers of bone and tissue are superimposed. Cone Beam Computerized Tomography uses precisely engineered reconstruction algorithms to extrapolate this data and reassemble the multiple layers of images into a precise, 3D representation that eliminates superimposition.
As the imaging receptor acquires the latent image data, it accumulates the data in a series of transverse slices. The focus and receptor are always in the plane of the slice to be acquired and the electromagnetic energy scans only this slice. Data points (integrals) are measured over this distribution and at points along curving structures. Separation and triangulation occurs during this measurement process. The measured intensity of electromagnetic energy as it passes through anatomical structures provides information about the sum of attenuation. The attenuation is the amount of intensity lost as the beam passes through the object. Each attenuation point contributes to hundreds of thousands of independent measurements that permit the computation of attenuation values for this specific two dimensional point of reference.
The distribution of attenuation values in each slice is examined independently, and provides data for a particular point in a two dimensional space. This point may then be computed against the totality of measured exposure intensities. The triangulated data is then reassembled, much the way a Rubik’s cube appears, with a mathematical value equal to the attenuation level assigned to each block in the colored cube. These values are viewed in shades of gray.
