II.A.35.     The HVL of an x-ray beam depends on the:

    a.     KV.    Yes

    b.     MAS.    No

    c.     Filter.    Yes

    d.     Focal-spot size.    No

   Discussion:    The HVL will be affected by any factor that changes the x-ray beam spectrum.   The two principal factors are KV and the amount of filtration.   Another factor which is not listed here would be the anode material.   For example, molybdenum produces a different spectrum (and HVL) than tungsten.

   Reference:    Physical Principles of Medical Imaging, 2nd Edition. pp. 161, 164