PURPOSE - Phase-contrast (PC) edge enhancement occurs at the boundary between different tissues and is an interference effect that results from the differential phase-shifts that the x-rays acquire while traversing the two tissues. While observable in planar phase-contrast radiographs, the impact of digital tomosynthesis on this edge enhancement effect has not been previously reported. The purpose of this work is to demonstrate: (1) that phase-contrast digital tomosynthesis (PC-DTS) is possible with a conventional x-ray source, (2) that the reconstructed tomosynthesis images demonstrate and retain edge enhancement as compared to planar phase-contrast radiographs and (3) tomosynthesis improves object contrast by reducing the effects of superimposed structures.
METHODS - An unmodified, commercially available cabinet x-ray system (Faxitron LX-60) was used. The system contains a tungsten anode x-ray tube that was operated at 24 kVp and 3 mAs for each PC radiographic image taken, with a nominal focal spot size of 0.010 mm. The digital detector uses CsI/CMOS with a pixel size of 0.054 mm x 0.054 mm. Objects to be imaged were attached to a computer-controlled rotating motor and are rotated +/- 25 degrees about a central position in one degree increments. At each increment, three phase-contrast radiographs are taken and then averaged to reduce the effect of noise. These planar images are then used to reconstruct a series of 56 longitudinal tomographic images with an image offset increment of about 0.7 mm.
RESULTS - Tomographic z-plane resolution was measured to be approximately 4 mm. When compared to planar PC images, the tomosynthesis images were shown to retain the PC boundary edge enhancement in addition to an improvement in object contrast.
CONCLUSIONS - Our work demonstrates that PC digital tomosynthesis retains the edge-enhancement observed in planar PC radiograph and further improves soft-tissue conspicuity by reducing the effects of superimposed tissue structure.