KEYWORDS: Signal to noise ratio, Imaging systems, X-ray imaging, X-rays, Diamond, Signal detection, Phase contrast, Signal attenuation, Deblurring, X-ray optics
Small angle x-ray scatter from microstructure too small to resolve in conventional imaging can provide an additional “dark field” signal that is complementary to attenuation and phase. Unfortunately, the low spatial coherence of clinical sources reduces dark field contrast. Focusing polycapillary optics are employed to allow for the use of high-power primary sources by increasing the phase signal after the focus. The method for this system is to structure the beam with a low-cost wire mesh that further relaxes the coherence requirement on the source. However, the coarseness of the mesh reduces the strength of the dark field signal compared with grating-based techniques, so optimization of the signal is important.
X-ray phase and dark field imaging offer two additional channels of information to enhance image contrast as well as providing information on material micro-texture that is unavailable to conventional x-ray imaging. These signals are commonly acquired by using multiple precisely aligned, fine-pitched gratings to both pattern the beam and to detect subtle shifts and blurring in this pattern. We instead use a single, low-cost, easily-aligned, coarse-pitched mesh to produce a pattern that is imaged directly to produce phase and dark field computed tomography (CT) images. We demonstrate phase and CT reconstructions using our system for a variety of phantoms.
X-ray phase imaging has found limited clinical use due to requirements on x-ray coherence that may not be easily translated to clinical practice. Instead, this work employs a conventional source to create structured illumination with a simple wire mesh. The system has been employed to produce high contrast absorption images with simultaneous differential phase contrast images. In previous work we have demonstrated accurate quantitative phase extraction. In this work, we have incorporated the dark field information to successfully reveal additional structure in low contrast objects.
X-ray images of low-density materials, such as soft tissue, provide inherently low contrast due to their subtle attenuation differences. However, differences in phase imparted to x rays can be substantial, giving significantly improved contrast. The barrier to widespread implementation of x-ray phase imaging is that most phase techniques require high spatial coherence of the x-ray beam. We have previously demonstrated that employing structured illumination produced by a stainless steel wire mesh can significantly loosen this coherence requirement. We present a computational model utilizing ray tracing that allows us to explore its design space and to optimize our phase reconstruction algorithms.
X-ray phase imaging has found limited clinical use due to requirements on x-ray coherence that may not be easily translated to clinical practice. Instead, this work employs a conventional source to create structured illumination with a simple wire mesh. A mesh-shifting algorithm that incorporates deconvolution of the source spot width is used to enhance resolution. Polycapillary optics are employed to enhance coherence. The effects of incorporating optics with two different focal lengths are compared. Measurements of fat embedded artificial tumors have been performed.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.