Serial Magnification Cerebral Angiography

Abstract

Cerebral angiography was first described by Egas Moniz in 1927 (6), and since that time there have been many technical developments which have resulted in improvement in diagnostic accuracy. Some of the more important are: (a) rapid serial film changers, both single and bi-plane; (b) mechanical injectors for standardization of pressure and rate of injection; (c) utilization of catheters for selective vascular injections; (d) stereoscopic and subtraction technics; (e) angiotomography; and (f) direct roentgenographic magnification. Magnification has been used for over fifteen years (1, 5, 7, 10) and applied in angiography as a single exposure technic (2, 3, 8, 9). We are currently performing serial roentgenographic magnification studies in cerebral angiography and consider it a valuable supplement to the examination of the intracranial vasculature. Since the technic results in enhancement of vascular details, its major usefulness has been in those instances when the small vessels are not clearly defined on conventional angiography. The magnification study is done immediately after review of the conventional study, as either a single or a bi-plane procedure, with precise positioning of the area under investigation. The serial study can be programmed in exactly the same way as the conventional examination so that all phases of the circulation are recorded. Technic A prerequisite for satisfactory direct roentgenographic magnification is an x-ray tube with a focal spot no greater than 0.3 mm. For serial studies the tube must be capable of withstanding the higher loadings that are required for high energy and short exposure technic; such tubes are on the market at the present time. A rigid film changer, whether of the roll-film or cut-film type, is also necessary in order to minimize motion during film transport. In order to obtain a twofold magnification the patient's head must be positioned midway between the target of the x-ray tube and the film. Under ordinary circumstances, the target-film distance is 40 in., and the support for the head is 20 in. from the film. Should the target-object distance be less than the object-film distance, greater than twofold magnification can be obtained, but a magnification beyond 2.5 to 3 × does not seem practical or advantageous. The other important technical factors required for serial angiography include: (a) short exposure time to minimize motion—1/30 to 1/10 second; (b) kilovoltage range—85 to 110 kV; (c) removal of grid—the use of the “air-gap” principle in the magnification technic obviates the need for a grid; (d) milliamperes—100 to 125 mA; (e) tight collimation of the x-ray beam; (f) high speed intensifying screens; and (g) fast film. A review of these factors indicates that everything is oriented in the direction of short exposure times so that motion unsharpness is reduced to a minimum.