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Consider the effect of the inverse square law.

Posted on November 16, 2018

Are you having difficulty getting enough X-ray signal in your digital radiography technique?


In film radiography we used a set focal distance for most techniques. This focal distance was fairly extensive due to the large focal spots being used, commonly 40in- 60in. With the smaller mini and microfocus tubes used in flat panel digital radiography, you can often operate at much shorter focal distances without the negative impact of geometric unsharpness. X-rays diverge when they are emitted from the tube anode and cover a larger area, thus losing their intensity per area with distance. The intensity of the X-ray beam decreases according to the square of the distance. Therefore, if the focal distance is cut in half the intensity will increase to four times the original. Consider the use of these shorter focal distances to provide a higher signal for a given kV and mA. This may also allow techniques with higher framerates to either speed up the acquisition or improve on signal to noise ratio with more frame averaging for a given acquisition time.


Digital Radiography
Inverse Square Law

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