Table 2. When the angle between the drill and vertical axis is less than or equal to 15°.

Drill radius (mm) 2 2.5 3 3.5 4
Numbers of checked cylinders 49 36 25 16 16
Whether found cylinder that drilling is available
Average Hounsfield value 718.9 774.7 797.5 591.6 458.4
Time complexity 72.4 52.1 33.6 23.1 27.8