What is the definition of source-to-image distance (SID)?

Source-to-image distance (SID) is defined as the distance from the anode focal spot, where the X-rays are generated, to the image receptor (IR) where the X-ray image is captured. This distance is crucial in radiography as it influences the image quality and the amount of radiation the patient receives. A longer SID typically reduces the magnitude of geometric distortion and increases image sharpness because it minimizes the divergence of the X-ray beam.

Additionally, SID affects the intensity of the radiation reaching the image receptor due to the inverse square law, which states that the intensity of radiation is inversely proportional to the square of the distance from the source. This emphasizes the importance of understanding SID when positioning the X-ray equipment to ensure optimal image quality while maintaining patient safety through careful radiation dose management.