Phototiming ensures what in chest radiography?

• A. Increased magnification of heart
• B. Reduced patient dose with consistent density
• C. Longer exposure
• D. More image noise

Answer: (B)

Phototiming is a form of automatic exposure control that terminates the X-ray exposure when a preset amount of light reaches the sensor. In chest radiography, the transmitted X-rays that pass through the chest are converted to light by a phosphor screen, and a photodetector senses this light. When the sensor detects the pre-set light level, the exposure ends, so the film receives a consistent amount of exposure regardless of patient size or technique variations. This keeps chest images with uniform density while reducing unnecessary radiation to the patient. It doesn’t change magnification, which is a geometric effect of distance, nor does it lengthen the exposure or inherently increase image noise; its goal is to standardize density and lower dose.