Keyhole cone device for lateral magnification cerebral angiography

Abstract

We have developed a new “keyhole” cone device for lateral magnification cerebral angiography. The keyhole lateral projection permits inclusion of the common carotid bifurcation, thereby eliminating the extra filming sequences and contrast injections required to delineate that structure. Magnification radiography has proved to be a valuable technique in the angiographic assessment of extracranial as well as intracranial vascular occlusive disease [1, 21. In addition, small focal spot magnification provides improved line pain resolution and permits lower patient radiation exposure dose. Because magnification radiography uses an air gap which produces a higher scatter radiation than conventional radiography, precise coning is imperative to avoid deterioration of the film image. Conventional coning devices cannot be used for magnification “keyhole” lateral projections because they are too long to permit the necessary 23 cm airgap between the head and the filmchanger and still maintain the required 100 cm target-to-film distance. Through a local vendor, we have developed a prototype lightweight (3 kg) magnification keyhole cone device that, at a target-to-film distance of 100 cm, permits an object-to-film air gap of 17.8-20.5 cm and has a magnification factor of 1.4. This device is interchangeable with larger, conventional keyhole cones. The only caution to potential users relates to the size of the cone base which varies with different models and manufacturers. The device described here has been tested by us in over 400 cerebral arteniognams and has produced films of excellent diagnostic quality. It has been used for anteroposterior magnification as well as lateral projections. The anteropostenior projection is accomplished by elevating the table to the level of the desired air gap. It has been our practice to employ the keyhole cone on all patients suspected of cerebrovascular occlusive disease and appropriate tumor suspects. The dimensions of the magnification keyhole cone are shown in figure 1 . In figure 2 the device is shown in use in a mock angiographic situation, and figure 3 demonstrates the quality of the resulting angiogram.