By default, the second image from the fluoroscopy series is used as a mask. However, the best results can usually be obtained when a frame preceding the first image with the contrast media appearance is selected as a mask.
To change the mask to the currently displayed image, click on the 
button or use the Shift + / shortcut.
Scroll through the series to see the changes in the DSA presentation.
The index of the selected mask is displayed in the bottom-left corner: 
To reset the mask image to the default, click on the 
button or press the Ctrl + Shift + / keys. This action will also revert any pixel-shift that has been applied to the mask.
