Illustration of the use of SPY to optimize placement of skin paddle for harvest of the anterolateral thigh (ALT) flap for reconstructive surgery. The proposed center of the ALT flap, in the right thigh, is marked in standard fashion at the midpoint of a line drawn between the anterior superior iliac spine (A) and the lateral patella (P) in preparation for harvest (Panel A). The colorized SPY Q analysis, shown in Panel B, identifies perforator perfusion zones in red along the AP line axis. The color SPY image is transposed over the native thigh in Panel C, showing the locations of perforator perfusion zones. Partial elevation of the ALT flap (Panel D) shows perforators (circled) emanating from the vastus lateralis muscle and rectus femoris muscle, corresponding to the perforator perfusion zones identified by SPY in Panels B and C. SPY will often show significant variation in perforator location, exposing the weakness of standard flap design.