Immediate Centering and Tomographic Cut Localization by Means of Roentgen Television

Positioning and ascertaining the correct pivot plane for tomographic sectioning is often a difficult as well as a time-consuming procedure. Several methods that reduce the number of trial exposures necessary for arriving at the desired section have been described in the past. Estimation of the correct level by applying anatomic knowledge is common. For example, a tomogram through the human hip joint will usually be located approximately 8 cm above the table top with the patient supine. Multisection tomography can also be used for estimation of the correct level, several cuts being taken through the region to be examined. However, the former method gives only a coarse approximation, and the latter produces considerable unsharpness due to the use of intensifying screens of varying speeds. Trigonometric methods for ascertaining the desired layer have been tried. Exposures in two extreme tube positions are taken, and the level sought is derived from the distance the object has wandered on the screen. The Siemens Universal Planigraph utilizes this method. Various tomoscopic devices have been suggested and described, but to our knowledge none of these has been used in practice.