Application of Diffraction Enhanced Imaging to Bone

Abstract

Diffraction enhanced imaging (DEI) is a new x-ray-based medical imaging modality that is in its early stages of development and testing. In images generated using DEI, contrast is from absorption and refraction of x-rays and from ultra-small angle x-ray scattering (USAXS). Though accepted values for x-ray absorption in biological tissues have been established, only recently have investigators began probing for characteristic refraction and USAXS from biological tissues. For this work, a series of four experiments were performed at the National Synchrotron Light Source (Upton, NY, USA) beamline X15A to help characterize DEI of bone. In the first experiment, the USAXS profile was measured for pre- and post-fatigue loaded cortical bone. Though no clear pattern of change in the USAXS profile was found, the bone samples were shown to have a measurable USAXS signal and it was found that large refracting structures within bone (>100 microns) could be visualized. In the next two experiments, the contrast of DEI?s refraction and apparent absorption images was compared to the contrast in synchrotron radiation (SR) radiographs for planar imaging of gap regions in bone and for imaging of trabecular structure in tomography mode. DEI was shown to have significant contrast-to-noise ratio gains over SR radiographs in both experiments. The planar refraction and apparent absorption signals in the gap imaging experiment were shown to be consistent with their theoretically predicted values. DEI in tomography mode (DECT) was found to have significant resolution gains over comparably obtained SRCT images. In the final experiment, a computer model was developed to predict USAXS from cortical bone and the computer model results were compared to USAXS data obtained using DEI. The scattering widths, as predicted by the computer model, suggest that osteocyte lacunae cause the experimentally measured angular spreading of the x-ray beam. The findings of these experiments provide the impetus for further studies of bone with DEI emphasizing clinical applications.