English to French Medical Medical: Cardiology

About heart imaging software. I understand both terms separately, but not together.

In order to obtain information on the spatial distribution of stationary pixels in the complete image, each of the 4 ***Gradient ROIs*** is placed in one quadrant of the image on a default position:
These ROIs can be made visible by selecting the Edit Gradient ROI button in the toolbar in step 2 ‘Define & Review Contours’.in the analysis window or via the Edit menu.
Each ***gradient ROI*** must be placed over a part of the body with no movement, as shown below:
Position and shape of each of the four ***Gradient ROIs*** is always copied over time.