Validation of dynamic radiography in the dog and evaluation of ischemic dyssynergy

If a collimated radiation detector (sodium iodide crystal) and a collimated X-ray source are positioned at right angles, scattered radiation will be sensed and the detector will generate a signal as tissue enters and leaves the "sensitive volume" formed by the intersection of the field of view of the detector and incident beam. This technique, called dynamic radiography, was used to identify and quantify the components of epicardial motion in anesthetized open-chested dogs. The data so obtained were validated by two independent optical methods: biplane cinematography and a technique that measures the shadow cast by the heart using a light beam-cadmium sulfide photocell. Displacement measured by dynamic radiography appeared to be the time integral of the scalar product of the velocity vector and the vector normal to the surface area within the sensitive volume, i.e., that component of displacement of myocardial mass that was perpendicular to the surface of the myocardium. In other words, the dynamic radiographic signal was proportional to the mass of tissue within the sensitive volume. Good agreement in terms of absolute motion, its direction, and phase was noted between predicted dynamic radiographic signals and those observed. Thus validated, this technique was found to be reliable in quantifying motion abnormalities produced by acute coronary ligation.