Imaging the Brain In Situ with Phase Contrast CT

Phase contrast X-ray imaging (PCXI) is an emerging modality that exploits the differing refractive indices of materials to create additional image contrast. When used in conjunction with computed tomography (CT), PCXI can produce images with greatly increased contrast resolution with respect to standard attenuation CT. This means that soft tissue boundaries that are typically not well resolved, such as those between the grey and white matter in the brain, can be visualized clearly. The brain poses unique problems for PCXI-CT, since it is fully encased in the highly-attenuating skull. Damage or defects in the imaging system and other physical effects result in inaccurate estimates of the attenuation gradient across high-contrast boundaries, causing distinct streak artifacts that can overwhelm the parts of the image that contain underlying tissues. In addition, ring artifacts caused by variations in X-ray beam intensity and detector response are more difficult to remove due to the roughly circular symmetry of the skull. Many common ring removal methods exploit the circular symmetry seen in ring artifacts and cannot distinguish between the skull and these artifacts.