Predicting the noise in hybrid (phase and attenuation) x-ray images acquired with the edge illumination technique.

PURPOSE: To analyze the noise performance of the edge illumination phase-based x-ray imaging technique when applying "single-shot" phase retrieval. The latter consists in applying a sample-specific low-pass filter to the raw data, leading to "hybrid" images in which phase and attenuation contrast are merged with each other. The second objective is to compare the hybrid images with attenuation-only images based on their respective signal-to-noise ratio (SNR). METHODS: Noise is propagated from the raw images into the retrieved hybrid images, yielding analytic expressions for the variances and noise power spectra of the latter. An expression for the relative SNR between hybrid and attenuation images is derived. A comparison with simulated data is performed. Experimental data are also shown and discussed in the context of the theory. RESULTS: The noise transfer into the retrieved hybrid images is strongly related to the setup and acquisition parameters, as well as the imaged sample itself. Consequently, the relative merit between hybrid and attenuation images also depends on these criteria. Generally, the hybrid approach tends to perform worse for highly attenuating samples, as the availability of phase contrast is outweighed by the loss of photons that is necessarily encountered in hybrid acquisitions. On the contrary, the hybrid approach can lead to a much better SNR for weakly attenuating samples, as here phase effects lead to much stronger contrast, outweighing the reduction in photon numbers. CONCLUSIONS: The analytic expressions inform the design of edge illumination setups that lead to minimum noise transfer into the retrieved hybrid images. We also anticipate our theory to guide the decision as to which imaging mode (hybrid or attenuation) to use in order to maximize SNR for a specific sample.

Subspace-based resolution-enhancing image reconstruction method for few-view differential phase-contrast tomography.

It is well known that properly designed image reconstruction methods can facilitate reductions in imaging doses and data-acquisition times in tomographic imaging. The ability to do so is particularly important for emerging modalities, such as differential x-ray phase-contrast tomography (D-XPCT), which are currently limited by these factors. An important application of D-XPCT is high-resolution imaging of biomedical samples. However, reconstructing high-resolution images from few-view tomographic measurements remains a challenging task due to the high-frequency information loss caused by data incompleteness. In this work, a subspace-based reconstruction strategy is proposed and investigated for use in few-view D-XPCT image reconstruction. By adopting a two-step approach, the proposed method can simultaneously recover high-frequency details within a certain region of interest while suppressing noise and/or artifacts globally. The proposed method is investigated by the use of few-view experimental data acquired by an edge-illumination D-XPCT scanner.

Long-term cryopreservation of decellularised oesophagi for tissue engineering clinical application.

Oesophageal tissue engineering is a therapeutic alternative when oesophageal replacement is required. Decellularised scaffolds are ideal as they are derived from tissue-specific extracellular matrix and are non-immunogenic. However, appropriate preservation may significantly affect scaffold behaviour. Here we aim to prove that an effective method for short- and long-term preservation can be applied to tissue engineered products allowing their translation to clinical application. Rabbit oesophagi were decellularised using the detergent-enzymatic treatment (DET), a combination of deionised water, sodium deoxycholate and DNase-I. Samples were stored in phosphate-buffered saline solution at 4°C (4°C) or slow cooled in medium with 10% Me2SO at -1°C/min followed by storage in liquid nitrogen (SCM). Structural and functional analyses were performed prior to and after 2 and 4 weeks and 3 and 6 months of storage under each condition. Efficient decellularisation was achieved after 2 cycles of DET as determined with histology and DNA quantification, with preservation of the ECM. Only the SCM method, commonly used for cell storage, maintained the architecture and biomechanical properties of the scaffold up to 6 months. On the contrary, 4°C method was effective for short-term storage but led to a progressive distortion and degradation of the tissue architecture at the following time points. Efficient storage allows a timely use of decellularised oesophagi, essential for clinical translation. Here we describe that slow cooling with cryoprotectant solution in liquid nitrogen vapour leads to reliable long-term storage of decellularised oesophageal scaffolds for tissue engineering purposes.

On the relative performance of edge illumination x-ray phase-contrast CT and conventional, attenuation-based CT.

PURPOSE: This article is aimed at comparing edge illumination (EI) x-ray phase contrast computed tomography (PCT) and conventional (attenuation-based) computed tomography (CT), based on their respective contrast and noise transfer. METHODS: The noise in raw projections obtained with EI PCT is propagated through every step of the data processing, including phase retrieval and tomographic reconstruction, leading to a description of the noise in the reconstructed phase tomograms. This is compared to the noise in corresponding attenuation tomograms obtained with CT. Specifically, a formula is derived that allows evaluating the relative performance of both modalities on the basis of their contrast-to-noise ratio (CNR), for a variety of experimental parameters. RESULTS: The noise power spectra of phase tomograms are shifted towards lower spatial frequencies, leading to a fundamentally different noise texture. The relative performance of EI PCT and CT, in terms of their CNR, is linked to spatial resolution: the CNR in phase tomograms is generally superior to that in attenuation tomograms for higher spatial resolutions (tens to hundreds of µm), but inferior for lower spatial resolutions (hundreds of µm to mm). CONCLUSION: These results imply that EI PCT could outperform CT in applications for which high spatial resolutions are key, e.g., small animal or specimen imaging.