Patent ID: 8433038

Claim:
An actual skin input dose rate computing device for use with an X-ray machine that includes an X-ray source, an X-ray detector disposed opposite to the X-ray source, and a supporting means for supporting a subject, said actual skin input dose rate computing device comprising: a distance sensor disposed in a direction directly opposite to the subject and close to an X-ray beam but not within the X-ray beam; an angle sensor disposed at the X-ray source; and a computing unit comprising: a judgment unit configured to determine whether an angle Φ sensed by said angle sensor is greater than or equal to 90 degrees or is less than 90 degrees; and a result unit configured to obtain actual skin input dose rate according to the result of said judgment unit and a relationship between a skin input dose rate at a reference position and the actual skin input dose rate, wherein said result unit comprises a first unit and a second unit, wherein if the angle Φ sensed by said angle sensor is greater than or equal to 90 degrees, said first unit computes the actual skin input dose rate using the following equation: R S = D 1 2 ( D 2 + D 3 ) 2 × R R wherein D 1 is a constant and indicates a distance between the X-ray source and the reference position, D 2 is a constant and indicates a distance between the X-ray source and said distance sensor, D 3 is a distance sensed by said distance sensor and R R is the skin input dose rate at the reference position; and if the angle Φ sensed by said angle sensor is less than 90 degrees, said second unit computes the actual skin input dose rate using the following equation: R S = D 1 2 ( D 2 + D 3 + D 5 COS ⁢ ⁢ Φ ) 2 × R R × ⅇ - K ⁢ D 5 COS ⁢ ⁢ Φ ⁢ ( 0 ⊕ D AL ) wherein D 1 is a constant and indicates the distance between the X-ray source and the reference position, D 2 is a constant and indicates the distance between the X-ray source and said distance sensor, D 3 is the distance sensed by said distance sensor, R R is the skin input dose rate at the reference position, D 5 is a thickness of the supporting means, K is a dose absorbing factor of aluminum, and D AL is an equivalent aluminum attenuation value of the supporting means.