FIGURE 1. Definition of regions for attenuation factor image. Bounding box, marked as rectangle surrounding patient, is determined from threshold image. Coordinates x_midline, y_head, y_upper, and y_legs are calculated using Equation 1 and are used to define head region (x[0, x_{end-of-matrix}], y[0, y_head]) (1), upper body (x[0, x_{end-of-matrix}], y[0, y_upper]) (2), pelvic region (x[0, x_{end-of-matrix}], y[y_upper, y_legs]) (3), right leg region (x[0, x_midline], y[y_legs, y_{end-of-matrix}]) (4), and left leg region (x[x_midline, x_{end-of-matrix}], y[y_legs, y_{end-of-matrix}]) (5).

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