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Focal Spot

The shape and size of a focal spot influence the resolution of a radiographic image. An increase in focal spot size, which may accompany deterioration of the x-ray tube, reduces the ability to define small structures.

Focal spot size is very important in any X-ray; literally focal spot is heart of X-ray machines. Smaller focal spot (0.4mm) with the smaller angle degree (12°) can provide the sharpest images whatever could be. Because smaller divergence angle of the X-ray beams make edges of the image on the film more accurately. You can get higher contrast and density of dental X-ray image by using the focal spot 0.4 mm comparing with 0.8mm used by most portable X-rays devices on market.

See the differences from 0.8mm and 0.4mm focal spot testing on the self-developed films.


Voltage - Power to penetrate bone.

We use Toshiba D-041 tube. So it helps Rextar series have 0.4mm focal spot, 12˚ of beams divergence and 70KV voltage tube power.

Powerful 70kv helps you obtain high-resolution X-ray image. No need to retake images. REXTAR's tube power has no differences from wall mounted or stand type X-ray machines. The main advantage of powerful 70kv is to eliminate blurred and unclear pictures of lateral teeth of maxilla and cheek bone.


Current is a flow of electric charge which means the quantity. In order to get a clear image, current of tube is also important factor. Moderate quantity of X-ray beams in 2mA helps to capture the root of teeth and intraoral nerves more clearly and protects users and patients from the exposure of unnecessary radiation dose.

Rextar's best tube power easily penetrates cheek bone and provides the sharpest and superior x-ray images.


The main consideration in any radiographic procedure involving human life is to reduce the leakage of radiation to patients and operators as much as possible while achieving the diagnostic goals. All Posdion's Rextar X-ray units are designed with safety in mind. Built-in leaded double-shield in Rextar series ensures that leakage from the x-ray source itself is almost eliminated; protecting the operators who is close to the device. In fact, the exposure from using Rextar X-ray unit is less than allowed occupation doses.

To characterize the REXTAR, leakage test of radiation were conducted at four different sites. As you can see the first four columns in table, almost no radiation was detected at one meter (100cm) distance. Then the probe was positioned at 5 cm from the leakage measurement of radiation. It was shown that Rextar radiation exposure is approximately 10mR. That means the results remain below the levels allowed by regulatory standards, under normal operation, FDA and CE limit (100mR/hr and 25 mR/hr respectively)