The overshoot artifact as an aid in differentiating low densities on the computed tomographic scan

This brief report describes an artifact that is seen as a thin, white rim outlining an air collection on the EMI 80 X 80 and 160 X 160 matrix CT scanners. This artifact is not associated with fat density and, therefore, its recognition allows presumptive differentiation between air and fat densities. The attenuation numbers of the lesion should then be obtained for confirmation.