New rapid roll-film changer.

Abstract

The purpose of this communication is to describe a new rapid roll-film changer which seems to overcome some of the drawbacks of presently used equipment. Rapid x-ray exposures during angiography are essential for hemodynamic and anatomic assessment of the vascular system. In spite of technical improvements in cineangiographic equipment, direct radiography remains indispensable for demonstration of fine vascular detail. Basic Considerations In the construction of a film-changer two basic principles can be used. The first, rapid changing of radiographic cassettes, has the advantage of assuring perfect screen contact. The rapid acceleration and deceleration of relatively heavy cassettes, however, causes excessive vibration. Our original choice of this approach prompted the development of an ultrathin and light vacuum cassette (1) which could be transported with ease. The disadvantages of this approach are the added work and cost required for the sealing of vacuum cassettes and the limitation of changing rate, which is considered to be at least five to six per second. For rapid angiography the second approach, namely, the intermittent closure of intensifying screens, is more suitable since only the relatively light x-ray film has to be transported, and vibration, although invariably present, occurs in the direction of the x-ray beam, thus minimizing blurring. The main difficulty with this design is not the film-transport system, but the achievement of a good film-screen contact. One major obstacle appears to be the trapping of air between film and screen, preventing intimate contact. Engineers have attempted to solve this problem by: (a) the closure of screens at one end first, similar to the closure of a book, and (b) the use of rigid convex plates which close in the center first, permitting air to escape toward the periphery. Since intimate contact between intensifying screen and radiographic film during exposure is of such great importance, numerous experimental devices have been investigated systematically at our laboratory during the past few years. These include mechanical, hydraulic, vacuum, and pneumatic closure mechanisms of the intensifying screen. A simple pneumatic device was chosen as compression device in the new changer. Compression Device Both intensifying screens are mounted on a thin Mylar membrane that is stretched tightly over a metallic frame which is part of a closed radiolucent air chamber (Fig. 1, A). Compressed gas with an inlet pressure of 10 pounds per square inch enters both chambers simultaneously through large port valves. The intensifying screens are thus forced against each other in such a way that they meet in the center first (Fig. 1, B) and air is wiped toward the periphery, minimizing airtrapping.