Radiation dose efficiency comparison between differential phase contrast CT and conventional absorption CT

Purpose: The superior radiation dose efficiency of a newly implemented differential phase contrast CT imaging method compared to the conventional absorption CT method is demonstrated. Methods: A differential phase contrast CT imaging method has recently been implemented using conventional x-ray sources with a grating interferometer consisting of three gratings. This approach offers the possibility of simultaneous reconstruction of both attenuation contrast and phase contrast images from a single acquisition. This enables a direct comparison of radiation dose efficiency of both types of reconstructed images under identical conditions. Radiation dose efficiency was studied by measuring the change in contrast-to-noise ratio (CNR) with different exposure levels. A physical phantom of 28.5 mm diameter was constructed and used for measurement of CNR in both the absorption and phase contrast CT images, which were reconstructed from the same data set. Results: For three of the four materials studied, at any given exposure level, the CNR of the differential phase contrast CT images was superior to that of the corresponding absorption contrast CT images. The most dramatic improvement was noted in the contrast between PMMA and water, where the CNR was improved by a factor of approximately 5.5 in the differential phase contrast CT images. Additionally, the CNR of phase contrast CT is empirically shown to have the same square root dependence on exposure, as is the case for absorption contrast CT. Conclusions: The differential phase contrast CT method provided higher CNR than conventional absorption CT at equivalent dose levels for most of the materials studied, and so may enable achievement of the same object visibility as conventional absorption CT methods at a lower exposure level. (C) 2010 American Association of Physicists in Medicine. [DOI: 10.1118/1.3425785]