3Periard , MA, Chaloner P. Diagnostic X - ray imaging quality assurance an overview[ J]. The Canadian Journal of Medical Radiation Technology, 1996, 27 (4) : 171 - 177.
4Maria Lucia Nana , Maria de Fatima A Magon, Yvone M Mas- carenhas. Evolution of X - ray machine quality controlaccep- tance indices[ J]. Journal of Applied Clinical Medical Phys- ics,2009, 10(4) : 252 -259.
5Periard MA,Chaloner P. Diagnostic X-ray imaging quality assurance an overview. Can J Med Radiat Technol, 1996, 27(4) :171 - 177.