1. Ziedses Des Plantes, B. G.: Subtraktion, Stuttgart: Georg Thieme 1961
2. Hanafee, W., Weidner, W., Oldendorf, W., Stern, W. E., Carndall, P.: Second Order Subtraction technique. Scientific Exhibit, VII Symposium Neuroradiologicum, New York, N. Y., Sept. 20?25, 1964
3. Oldendorf, W. H.: A modified subtraction technique for extreme enhancement of angiographic detail. Neurology (Minneap.) 15, 336?370 (1965)
4. Hanafee, W., Shinno, J. M.: Second-Order Subtraction with Simultaneous Bilateral Carotid, Internal Carotid Injections. Radiology, 86, 334?341 (1966)
5. Publications Division, E.I. Du Pont De Nemours & Co., Photo Products Department, Wilmington, Delaware, 19898