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If the brain recognizes a lesion, then the third phase is diagnosis. In this phase the brain determines whether the lesion is real or not and what, if any, significance to ascribe to it. The interpretation phase may be affected by such factors as clinical suspicions or prejudices and observer experience. This complex lesion detection process occurs very quickly. Many people spend a few minutes studying a radiograph, but in ultrasonography the brain is presented with 10 to 20 images per second to analyze. The intricacy of the process leaves it open to many sources of error. Poor viewing conditions, complacency, or inadequate attention may result in failure to fix the lesion. The brain may fail to recognize an abnormality as such, especially in inexperienced observers. A lesion may be dismissed as a normal anatomic variant or an artifact. Alternatively, an insignificant finding, an artifact, or normal variant may be interpreted as an important lesion. The ability to quickly and confidently recognize normal structures distinguishes experienced radiologists from others when interpreting images. The observer’s level of experience and any preconceived ideas about likely diagnoses have major impact on the detection process. Bias or preconceived ideas are also likely to result in an erroneous conclusion about the significance of a lesion. In all cases, regardless of experience, observers either under-read or over-read diagnostic images depending on their biases, perceived consequences of a false-negative or false-positive diagnosis, and personality traits. Errors may also arise due to the phenomenon of “satisfaction of search,” wherein, having discovered one or two lesions, the observer ceases the search for abnormalities and fails to detect additional lesions. This kind of error tends to compound itself because, if a lesion is not detected on the first examination, then it is likely to go undetected during later examinations as there is no impetus to look for it. Interpretation of diagnostic images is an exacting process, and even highly skilled and experienced practitioners will make mistakes. A number of methods can be adopted to minimize errors. First, every effort should be made to achieve an optimum quality image. An accurate radiographic technique chart for all body parts should always be used. Processing artifacts can be minimized by good darkroom hygiene, careful attention to chemistry formulation, and routine maintenance and cleaning of processing tanks or the automatic processor. Radiographic variables, such as positioning and film or screen type, should be kept constant. If all studies performed are of diagnostic quality, then a strong foundation for interpretation has been established. For difficult cases, good-quality images are more likely to yield a diagnosis if submitted to a radiologist.

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