Fig. 1

Design of the phantom. All sizes are in millimeters. The height is lower than the smallest axial field of view of the PET/CT scanners included for calibration. The phantom consists of solid polyethylene (light gray) and contains six openings (indicated 1 to 6; 3 to 6 colored white). In each opening, a polyethylene socket can be placed tightly, enclosing an amber glass vial (dark gray, wall thickness about 1.5 mm) of 2 mL inner volume, filled with ¹²⁴I activity (shaded). The position of the vials in the phantom is such that the ¹²⁴I positrons (maximum range r) do not interfere between the vials and do not reach the outside of the phantom. The vials have a neck and screw cap, so the shape and height are an indication