Derivation of total filtration thickness for diagnostic x-ray source assembly. 
The method defined by the IEC 60522 for determining the inherent filtration of an x-ray source device is applicable only for a limited range of tube voltage.  Because the users cannot legally remove the x-ray movable diaphragm of the x-ray source device, total filtration, which is the sum of the additional filtration diaphragm movable for specific filtration and x-ray, cannot be measured.  We develop a method for simply obtaining the total filtration for different tube voltage values.  Total filtration can be estimated from a ratio R' of the air kerma [Formula: see text], which is measured with an Al plate with thickness T, and [Formula: see text] measured without an Al plate.  The conditions of the target material of the x-ray source device are then entered into the Report 78 Spectrum Processor to calculate the air kerma K x and K x+T for Al thicknesses x and (x + T), respectively, to obtain R. The minimum value of x, which is the difference between the R and R', is the total filtration of the x-ray source device.  The total filtration calculated using the industrial x-ray source device was within ±1% in the 40-120 kV range.  This method can calculate the total filtration using air kerma measurements with and without the Al plate.  Therefore, the load on the x-ray tube can be reduced, and preparation of multiple Al plates is not necessary.  Furthermore, for the 40-120 kV tube voltage range, the user can easily measure the total filtration.