2. X-RAY COLLIMATION CHANGES
Collimating the X-ray beam to the precise size of the image receptor eliminates scatter radiation. Most vendors produce large,DENTRIX round cones with large X-ray beam patterns so the operator “cannot miss” the film or receptor. This not only adds scatter radiation, reducing image quality, but also adds significantly to the patient’s X-ray dosage. Scatter radiation to any receptor—film, sensor, or phosphor plate dramatically reduces image quality. The new report mandates the use of a rectangular collimator. This is actually GOOD news for image quality, but may make assistants shudder because of the smaller area of the beam. They might think that they will produce more errors such as “cone cuts” and “missed apices.” And they might. However, help is on the way!
Dentists and their auxiliaries will have to use a rectangular collimator of the precise size of the image receptor. This will improve the images taken by reducing scatter radiation. This collimation also reduces the patient’s skin surface X-ray dosage by almost 60%, simply because the beam size is so much smaller—but “Where’s the help?”
The NCRP report #145 states: "Rectangular collimation of the beam shall be used routinely for periapical radiography. Each dimension of the beam, measured in the plane of the image receptor should not exceed the dimension of the image receptor by more than 2% of the source-to-image receptor distance. Similar collimation shall be used, when feasible, for interproximal (bitewing) radiography."
The following are means to convert to rectangular collimation
Masel film holder & positioning device
Rinn Rectangular collimator
Margraf rectangular cone
IDI TruImage™
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