Measurement of the MTF of a Cone-Beam Breast Computed Tomography Laboratory Scanner

We measured the spatial resolution of the prototype scanner developed for laboratory investigations on Cone-Beam Breast Computed Tomography (CBBCT). The scanner has potential for high spatial resolution, since it employs a minifocus X-ray tube (0.04 mm nominal focal spot size) and a fine pitch (0.05 mm) flat panel detector. With the available maximum tube current (0.25 mA) and detector field of view (120 × 120 mm²), adequate sample volume coverage and exposure requirements as in a clinical scan are obtained via increasing the total acquisition time and by combining laterally translated projections at each angular position. The Modulation Transfer Function (MTF) of the system was evaluated in step-and-shoot acquisitions with the tilted wire method, by imaging a test pattern made by an array of vertical and horizontal thin metal wires. MTF measurements in each tomographic plane were performed. Spatial frequency values of 3-3.5 mm^{- 1} at 10% MTF were measured. A lower spatial resolution performance is expected in continuous acquisitions, due to the gantry motion blur.