Use of the Eyes in X-Ray Diagnosis

Have you ever missed a perfectly obvious rib fracture? Or overlooked an obvious lung infiltration? If so, you have known real discomfort–the inability to explain such an oversight to your colleagues, for it is far more inexplicable than an error in diagnosing what you actually saw. Let us try to explain why these things happen, and attempt to justify systems which will make these accidents less likely. For we must have systems. Children who take a standard intelligence test (Terman) are given this problem: “You have lost a ball in this round field. Here is the gate. With your pencil show me how you would look for it.” With this test the child of eight years will show some system, while the one of twelve is expected to sketch a regular plan. If we are to develop a routine for scanning films, what approach shall we use? Two systems present themselves: the anatomical and the psychological. In some situations there is no problem. In a retrograde pyelogram one could scarcely do other than look at the kidneys and then the ureters and bladder. In upper gastrointestinal films, one naturally follows with the eye the course of the barium. Elsewhere, however, the body is not so obliging. Can the psychology of seeing help us here? Size of the Visual Field The eyes are capable of optically registering a fairly sharp image of most of a 14 × 17-inch film at one fixation, provided the viewer does not stand too close. But whether or not that view is psychically registered is a different matter. We are so conditioned to fixing our attention that only the center of the field may reach our consciousness. Yet the ability to comprehend the whole field can be cultivated. During World War II, speed in aircraft recognition became so important that men were trained to identify objects in fractional exposures, down to 1/100 of a second, by being taught to perceive larger visual fields. Cannot the same thing be done in radiology? We believe that unconsciously this skill is developed in chest film reading. This is easily understandable in the case of miniature films, where the whole picture is seen in a small field. But even large films (14 × 17 in.) can usually be recognized as positive or negative by the expert about as fast as they can be put up. He has expanded his visual fields to comprehend all he sees in a postero-anterior projection. He does not find this so easy in the case of lateral or oblique views as a rule, because he has not the thousands of previous experiences from which to draw. Nor can he do it on a heavily exposed film, which requires more minute inspection. But few men would aver that they can read films of all sorts at a glance. What is their system in scanning? Questioning radiologists has not been helpful: some simply say they look at what interests them; others report their own private methods, which they admit are not particularly rational.