The plate under the patient also moves, but in the opposite direction.
Suppose an X-ray exposure lasts five seconds. The ray will be passing through the centre of the imaginary wheel for the whole five seconds, because whatever the position of a wheel in motion its centre is stationary. i That means that the point selected by the specialist will be photographed.
Bat all the other parts of the body around this point are not the centre of the wheel. The X-ray only passes through them for a fraction of the time, one after another.
The result is exactly the same as when a photographer is giving a time exposure of a street in the evening.
The street comes out, but passers-by who just flit in front of the camera for a second do not come out.
So in the tomograph, only the part at the stationary point of the moving ray comes out and the other parts of the body just "fit by." On the plate they are just a blur.
Wide Praise t The tomograph, in short, enables the X-ray to "see round corners."
Text read from the printed page and cleaned; old type leaves the occasional error.