Spatial dependency of multiplanar reconstruction in digital breast tomosynthesis.

Tomosynthesis acquires projections over a limited angular range, resulting in anisotropic sampling in the Fourier domain. The volume of the sampled space is therefore spatially dependent; different Fourier components are sampled for the same object, depending upon where the object is located relative to the system origin. A next-generation tomosynthesis (NGT) system was developed at the University of Pennsylvania to increase the spatial isotropy in DBT, by incorporating additional system motions. In this work, we investigate the spatial dependency of image quality in tomosynthesis and compare conventional and NGT tomosynthesis in terms of multiplanar reconstruction (MPR). Two test objects, a high-frequency star pattern and a low-frequency octagon phantom, were placed throughout the detector field of view at various obliquities to analyze the anisotropic nature of tomosynthesis. Reconstructions of the star pattern were analyzed both qualitatively and quantitatively using the Fourier distortion metric (FSD). Reconstructions of the octagon phantom were analyzed qualitatively. In a separate experiment, a container filled with water and acrylic beads of various diameters were imaged at various locations to simulate low-contrast objects mimicking breast tissue. We show that the spatial dependency of MPR is unique to the tilt angle, orientation, and frequency of the input. The NGT geometry benefitted the visualization of objects by reducing the out-of-plane artifacts in MPR.