OK, I just measured the exit channel of the X-ray machine to be ~17 inch tall. Since the belt bends somewhat in the vertical direction, but not in the horizontal, more buffer space needs to be left in the vertical direction, but still be plenty should be left. Nominally then, the box one needs to squeeze into is 24"x17". According to atman one should not exceed 23" in the horizontal direction by more than a tad. My bet would be that the similar vertical distance would be 15".