Visual representation of symmetric pulse spacing (F1 = F2) on an Archimedean spiral, shown for different values of the product of scaling factors F1 and F2. Left: F1 · F2 = 1, adjacent bubbles do not overlap in the two principal directions and diagonal directions leaving tissue bridges. Middle: F1 · F2 = 2, adjacent bubbles largely overlap in the two principal directions and just overlap in the two diagonal directions leaving no tissue bridges. Right: F1 · F2 = 1.41, A good compromise that enables tissue bridge-free bubble overlap while minimizing the dose.