Figure 2. Procedure used for determining the number of counts present in the thyroid in order to obtain the ^99mTc-pertechnetate uptake. From an image obtained in the anterior projection (A), a circular region of interest (ROI) was positioned around the entire gland excluding other structures, such as the salivary glands (B). Using an edge detection program, the computer drew the contour of the thyroid gland (C) and determined the number of counts in this region. For background subtraction, another ROI was drawn immediately below the thyroid gland (D). Except for the positioning of the circular ROI, the entire process was automatic and took only a few seconds.