The primary objective of the research in this thesis is to evaluate the performance of the high-energy in-line phase contrast prototype with the conventional mammography along with ultrasound systems in the detection of tumors within dense breasts. Mammography is the gold standard for breast cancer screening. The accuracy of conventional mammography decreases in imaging of dense breasts. Additional screening with supplemental modality, such as ultrasound, increases the rate of early detection of breast cancer in women with dense breasts. However, the ultrasound also has the disadvantages of operator dependent, high false-positive rate, etc. Therefore, there is room for the improvement in mammography particularly in dense breast imaging. Phase contrast x-ray imaging provides a unique opportunity in improving the accuracy of cancer detection in breast imaging. Phase contrast imaging relies not only on the attenuation coefficients but also on the effects produced by x-ray phase shift coefficients. In this study, three breast phantoms are used for imaging comparisons. The first phantom containing simulated tumors is commercially manufactured in 50-50 glandular-adipose ratio (50G-50A). Two phantoms in 70-30 glandular-adipose ratio (70G-30A) are custom made with one phantom embedded with gelatin blocks and the other phantom embedded with carbon fiber disks to simulate various tumor sizes. The phase contrast images are acquired with optimized operating parameters. With the preliminary study of 50G-50A phantom, the results indicate that the conventional technique is not able to detect the tumor-like object while the ultrasound and the in-line phase contrast prototype are able to detect the object in the phantom, under the specific experimental condition. For both the 70G-30A phantoms, conventional technique did not xii detect any objects, ultrasound detected all the objects while the phase contrast imaging detected more than 60% of the embedded tumor-like objects. The results of the research in this thesis demonstrate that the high-energy in-line phase contrast imaging has the potential to be a standalone modality in screening of breast cancer.