Evaluation of a compact multicontrast and multiresolution X‐ray phase contrast edge illumination system for small animal imaging

Abstract

Purpose In this work the performance of a compact multiresolution and multicontrast x‐ray phase system based on edge illumination is investigated. It has been designed for small animal imaging and with a limited footprint for ease of deployment in laboratories. Methods The presented edge illumination system is based on a compact microfocus tungsten x‐ray source combined with a flat panel detector. The source has a maximum output of 10 W when the minimum spot size of about 15 μm is used. The system has an overall length of 70 cm. A new double sample mask design, obtained by arranging both skipped and nonskipped configurations on the same structure, provides dual resolution capability. To test the system, we carried out computed tomography (CT) scans of a plastic phantom with different source settings using both single‐image and multi‐image acquisition schemes at different spatial resolutions. In addition, CT scans of an ex‐vivo mouse specimen were acquired at the best identified working conditions to demonstrate the application of the presented system to small animal imaging. Results We found this system delivers good image quality, allowing for an efficient material separation and improving detail visibility in small animals thanks to the higher signal‐to‐noise ratio (SNR) of phase contrast with respect to conventional attenuation contrast. The system offers high versatility in terms of spatial resolution thanks to the double sample mask design integrated into a single scanner. The availability of both multi‐ and single‐image acquisition schemes coupled with their dedicated retrieval algorithms, allows different working modes which can be selected based on user preference. Multi‐image acquisition provides quantitative separation of the real and imaginary part of the refractive index, however, it requires a long scanning time. On the other hand, the single image approach delivers the best material separation and image quality at all the investigated source settings with a shorter scanning time but at the cost of quantitativeness. Finally, we also observed that the single image approach combined with a high‐power x‐ray source may result in a fast acquisition protocol compatible with in‐vivo imaging.

Volumetric High-Resolution X-Ray Phase-Contrast Virtual Histology of Breast Specimens With a Compact Laboratory System

“…The use of two different sets of masks required user intervention to switch between low-and high-resolution modes, with consequent need for system realignment. However, we have recently shown that skipped and non-skipped designs can be simultaneously arranged on the same mask [28]. This allows for the design of a multi-purpose CT scan: such a machine could be used for both low-resolution intra-operative applications and for high-resolution virtual histology, simply by laterally displacement of a mask featuring both designs.…”

“…While the first assumption is verified by a large number of specimens, the latter is strictly true only for single material specimens. However, even in cases where this condition is not strictly verified, single image retrieval still provides high image quality with low noise, at the expense of quantitative significance [28], [41]. Under the above assumptions, a retrieved image can be obtained as: µ(x, y, z)dz = −log F −1 F {I(x, y)/I 0 } 1 − 2πiz od IC(s i )/IC (s i )γf x…”

Replacing the detector mask with a structured scintillator in edge-illumination x-ray phase contrast imaging

“…Two different EI setups have been used, a conventional one featuring two masks and a flat panel detector as used in previous work, and a single (sample) mask one using the CCD camera with the structured scintillator 18 . Both are "compact" setups which follow the design recently implemented for intra-operative specimen imaging 19,20 , resulting from the previous demonstration that reducing the system length at constant magnification does not negatively affect the (phase) signal-to-noise ratio if the exposure time is kept constant 21 .…”

Edge-illumination x-ray phase-contrast imaging

“…To tackle this, we developed an adaptation to EI [ 98 ] of Beltram et al ’s approach [ 99 ], which deals with this problem by reconstructing interfaces one at a time by using a different δ to β ratio for each, then splicing together the results. Preliminary studies on small animal imaging have been conducted with promising results [ 100 , 101 ], which led to additional research currently underway.…”