and image quality in x-ray–based examinations. Recent advances in computed tomographic
(CT) technology, including implementation of automatic tube current modulation
(ATCM), allow reduction in radiation exposure during CT examinations (1– 6). ATCM
may be defined as a set of techniques that enable automatic adjustment of the tube current
in the x-y plane (angular modulation) or along the z-axis (z-axis modulation) according to
the size and attenuation characteristics of the body part being scanned and achieve
constant CT image quality with lower radiation exposure. Hence, ATCM techniques are
analogous to the automatic exposure-control or photograph-timing techniques used in
conventional radiography.