Contrast

Contrast (Azim Celik, General Electric Company, Milwaukee, Wisconsin and Weili Lin, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina). SNR (signal-to-noise ratio) determines the effectiveness of an imaging experiment. However, even the highest SNR does not guarantee the usefulness of an image. An important aim of imaging for diagnostic purposes is to be able to distinguish between diseased and neighboring normal tissues. If the imaging method used does not have a signal-manipulating mechanism which produces different signals for the diseased and normal tissues, then distinguishing the two tissues is not possible. This unit provides a detailed discussion of the contrast-producing mechanisms that arise from the signal dependence on a wide variety of tissue parameters.