As industrial computed tomography (CT) systems evolve toward robotic CT and freely selectable three-dimensional acquisition trajectories, spatial resolution must be evaluated not only globally but also with respect to position and direction within the three-dimensional measuring volume. The modulation transfer function (MTF) is a key metric for spatial resolution, yet the widely used ASTM E1695−20 method, based on edge response analysis of cylindrical objects, provides only averaged axial-plane values and lacks directional information. To overcome these limitations, this contribution proposes an extended MTF evaluation approach suitable for advanced 3D trajectories. The method analyzes individual gray value profiles along lines perpendicular to object surfaces and applies local averaging to improve robustness against voxel grid effects and noise. While a cylindrical object is used for comparability with ASTM E1695−20, a spherical object enables full 3D directional MTF assessment.