Technical Design Considerations of a Human-Scale Talbot-Lau Interferometer for Dark-Field CT

Abstract

Computed tomography (CT) as an important clinical diagnostics method can profit from extension with dark-field imaging, as it is currently restricted to X-rays' attenuation contrast only. Dark-field imaging allows access to more tissue properties, such as micro-structural texture or porosity. The up-scaling process to clinical scale is complex because several design constraints must be considered. The two most important ones are that the finest grating is limited by current manufacturing technology to a 4.8 µm period and that the interferometer should fit into the CT gantry with minimal modifications only. In this work we discuss why an inverse interferometer and a triangular G 1 profile are advantageous and make a compact and sensitive interferometer implementation feasible. Our evaluation of the triangular grating profile reveals a deviation in the interference pattern compared to standard grating profiles, which must be considered in the subsequent data processing. An analysis of the grating orientation demonstrates that currently only a vertical layout can be combined with cylindrical bending of the gratings. We also provide an indepth discussion, including a new simulation approach, of the impact of the extended X-ray source spot which can lead to large performance loss and present supporting experimental results. This analysis reveals a vastly increased sensitivity to geometry and grating period deviations, which must be considered early in the system design process.

Dark-field chest X-ray imaging for the assessment of COVID-19-pneumonia

“…Depending on setup-specific parameters, such as the length of the interferometer and X-ray spectrum, the grating parameters, such as duty cycle and lamella height, need to be adapted for maximum visibility. Therefore, a propagation and simulation framework for X-ray grating interferometers was created to optimise these grating parameters 27 . An exemplary simulated visibility map for optimising G1 height and duty cycle can be found in Fig.…”

Initial Characterization of Dark-Field CT on a Clinical Gantry

“…It is in an inverse geometry where two X-ray compatible optical gratings, referred to as G 0 and G 1 , are positioned close to the X-ray source in front of the patient and the third grating (G 2 ) is placed on the other side of the bore in front of the detector [22]. As discussed in [19], this geometry is advantageous for implementation into a clinical CT gantry because only relatively small gratings G 0 and G 1 are required and the available space close to the source is efficiently used.…”

“…Cylindrical dark-field CT design with an inverse Talbot-Lau interferometer consisting of bent gratings. The design has been introduced in [19] and makes the best use of the available space in a clinical CT gantry, maintaining the original bore diameter of 70 cm. The field of view is the highlighted area with a diameter of 45 cm, which is only 10% smaller than the original field of view shown in green.…”

“…In [19], we discussed the fundamental design criteria of our prototype, including details on the geometric and grating parameters. The first results from the implementation and initial description have been published in [11].…”

“…In this paper, we present a detailed analysis and characterization of the dark-field CT prototype, which has been designed in [19] and was initially presented in [11]. Our focus lies particularly on the experienced vibrations, the interferometer performance, the radiation dose, and the 3D-imaging performance.…”