After the introduction of multi-detector CT, significant attention was given to doses and associated risks from CT. In spiral CT, reconstruction algorithms require a number of additional rotations to reconstruct the first and last slice of imaged volume. Z-overscanning refers to the extent of the tissue beyond the boundaries of the volume to be imaged that is exposed to X-rays. The increase in patient effective dose due to z-overscanning may reach 36% for a 16-slice CT system [47]. In hip MDQCT and HR MDCT imaging the influence of z-overscanning on the patient effective dose should always be taken into account. Careful selection of beam collimation, reconstructed image slice width and pitch is needed to limit the extent of z-overscanning [48]. A recent study showed that adaptive section collimation allows considerable dose reduction of unnecessary exposure due to z-overscanning [49].