Past and future of radiologic error

Although radiographs are extremely important in clinical medicine, their interpretation is susceptible to significanterror: mistakes in detection and interpretation result in a false negative rate of 30-40%. This figure has not changed withnearly two generations of research.What are some of the contributing factors? First, consider the complexity of the radiologic images with all thevariable human anatomy and potential pathology. The radiograph is a two-dimensional projection of a three-dimensionalstructure, so that there are many superimposed structures to be sorted out. This superimposition is eliminated with cross-sectional imaging techniques, such as computed tomography (CT) and magnetic resonance imaging (MRI), but at great cost.Further, their interpretation is complicated by the large number of images which must be mentally assembled to cover theentire subject.The term "conspicuity" was coined to represent the potential of a radiographic finding to be detected, as influencedby its size, contrast, and background complexity. These are complex functions of not only the pathology but also theradiological technique. Suffice it to say that there is great variability in the conspicuity of the abnormalities to be detected inclinical practice.Another major topic to consider is the physiological limitations of the human eye; specifically, the limited extentof foveal coverage with reduced contrast detection and detail resolution by the rest of the retina. The way a radiograph isexamined is a technique learned by practice, and differs among practitoners. This search pattern, described by researchers whotrack eye movement, consists of fixations and rapid movements, so that the fovea covers only a minority of the film surface.Scanning by eye does not provide the systematic coverage of a television raster. Large shadows in the lungs can be readilydetected by peripheral vision, but any lesion of low conspicuity must be looked at directly, with foveal vision, in order to bedetected. How this is achieved is based on clinical understanding of where obscure findings should be sought.Studies of the cases missed in clinical radiology (mainly studies of lung cancer detection) reveal two maintroublesome regions in the chest: the periphery, where small lesions lurk; and the hilar region, whose deformity by tumor ispoorly recognized, or which hide lesions behind them. I have noted the upper medial portions of the lungs are a difficultregion in which to distinguish overlapping bone and vessel shadows from possible tumors. Regions hidden by the heart,because of relative underexposure, have less contrast available, and so peripheral vision isn't good enough. Theseconsiderations should be reflected in a well-tailored personal search pattern.It has long been recognized that the clinical history affects search patterns, a form of bias. This will affect thelikelihood of detection of a finding. On the other hand, the clinical information implies the prior probabilities that facilitateinterpretation of a finding. Those who have advocated interpreting radiographs while ignorant of the clinical history captureonly half the picture, however. The other half follows a directed search for radiographic findings, based on the differentialdiagnosis (clinically) of the patient's history and other findings. I advocate interpreting all films both with and without thehistory, sometimes requiring some mental gymnastics by the radiologist.