In the temporal subtraction processing technique, what is superimposed to produce the final image?

In the temporal subtraction processing technique, the process involves using a mask image that represents a prior time point, usually before contrast media has been administered. This mask image is combined with a subsequent image acquired after the contrast has been injected.

When the mask and contrast images are combined, areas that have not changed over time—such as static structures—are effectively suppressed or canceled out from the final image. This allows enhanced visual clarity of dynamic changes or new anomalies, like vascular lesions that appear after contrast administration.

The principle relies on the ability to distinguish between the two images: the mask, which typically highlights stable anatomical features, and the contrast-enhanced image, which reveals physiological changes. The final image, therefore, prominently displays only the regions of interest where changes have occurred, facilitating a clearer diagnosis.

Understanding this technique is essential in medical imaging, especially in dynamic studies of blood flow and other physiological changes, as it dramatically improves the visualization of significant clinical findings.