Technical Note: Practical implementation strategies of cycloidal computed tomography

Abstract

Purpose: Cycloidal computed tomography is a novel imaging concept which combines a highly structured x-ray beam, offset lateral under-sampling, and mathematical data recovery to obtain highresolution images efficiently and flexibly, even with relatively large source focal spots and detector pixels. The method reduces scanning time and, potentially, delivered dose compared to other sampling schemes. This study aims to present and discuss several implementation strategies for cycloidal computed tomography (CT) in order to increase its ease of use and facilitate uptake within the imaging community. Methods: The different implementation strategies presented are step-and-shoot, continuous unidirectional, continuous back-and-forth, and continuous pixel-wise scanning. In step-and-shoot scans the sample remains stationary while frames are acquired, whereas in all other cases the sample moves through the scanner continuously. The difference between the continuous approaches is the trajectory by which the sample moves within the field of view. Results: All four implementation strategies are compatible with a standard table-top x-ray setup. With the experimental setup applied here, step-and-shoot acquisitions yield the best spatial resolution (around 30 µm), but are the most time-consuming (1.4 h). Continuous unidirectional and back-andforth images have resolution between 30 and 40 µm, and are faster (35 min). Continuous pixel-wise images are equally time-efficient, although technical challenges caused a small loss in image quality with a resolution of about 50 µm. Conclusion:The authors show that cycloidal CT can be implemented in a variety of ways with high quality results. They believe this posits cycloidal CT as a powerful imaging alternative to more timeconsuming and less flexible methods in the field.

Exploring the potential of cycloidal computed tomography for advancing intraoperative specimen imaging

“…In step-and-shoot scans, the repeated stop-starting of the rotation and translation motors can lead to significant overheads. On the contrary, cycloidal acquisitions can be realized as flyscans 27 , where the sample is simultaneously rotated and translated without interruption. Provided that the detector integration time is negligible, overheads are removed and scan time is equal to exposure time.…”

“…Previous work has shown that an even coverage of the sinogram, as can be seen in panel (c), provides a favourable configuration for recovering the missing data using mathematical methods 6 . Simulations and experimental results suggest that cycloidal CT can yield a resolution comparable to dithering without having to apply time-consuming step-scanning of the sample at each rotational position 27 .…”

“…Cycloidal computed tomography 6,27 refers to an imaging concept by which the abovementioned under-sampling problem is alleviated in a different manner. Rather than step-scanning the sample for each rotational position, as is done in dithering, the sample is translated as it rotates.…”

“…Data recovery can be performed with a variety of methods. Initially we used bicubic splines to interpolate under-sampled cycloidal sinograms, due to their availability as in-built functions in standard image processing software 6,27 . More recently, we have integrated a convolutional neural network (CNN) layer into the processing, which utilises learned relationships between interpolated and dithered data to improve image quality 28 .…”

Modulation transfer function (MTF) evaluation for x-ray phase imaging system employing attenuation masks

“…effectively sampled at a frequency higher than the pixel pitch) MTF 31,32 . The A c c e p t e d M a n u s c r i p t 6 relevance of this work goes beyond EI XPCI and is more generally applicable to methods using pre-sample masks, either to gain access to some degree of phase-based image contrast or specifically to increase the resolution [33][34][35][36] .…”