The scintillator converts the X-rays that strike the sensor into light. The high-energy photons of the X-rays excite particles of the scintillator material as they pass through it. These particles then emit light in the visible frequency spectrum. This makes it possible to use conventional silicon based photosensitive elements to record the image. The individual pixels of an area sensor are not exactly identical in sensitivity. This difference is automatically eliminated in practice by calibrating the sensor under bright and dark X-ray illumination and applying automatic software correction. Typical area sensors have about 1000 × 1000 or 2000 × 2000 pixels. The dimensions of the pixels are between 50 and 400 µm. The size of the sensor determines the largest possible object that can be measured “in the image” at low magnification without using raster tomography. For the same cone angle, a larger area sensor requires a larger measuring machine than a smaller sensor. Large sensors therefore make sense only if a large measurement area is required.

See the image above: The X-ray image is converted into an image in the visible spectrum by the scintillator (a). The photo sensor array (b) converts this into electronic signals.