A new iterative algorithm to reconstruct the refractive index

Model-based adaptive filter for a dedicated cardiovascular CT scanner: Assessment of image noise, sharpness and quality

BACKGROUND

Filtered back projection (FBP) and adaptive statistical iterative reconstruction (ASIR) are ubiquitously applied in the reconstruction of coronary CT angiography (CCTA) datasets. However, currently no data is available on the impact of a model-based adaptive filter (MBAF2), recently developed for a dedicated cardiac scanner.

PURPOSE

Our aim was to determine the effect of MBAF2 on subjective and objective image quality parameters of coronary arteries on CCTA.

METHODS

Images of 102 consecutive patients referred for CCTA were evaluated. Four reconstructions of coronary images (FBP, ASIR, MBAF2, ASIR + MBAF2) were co-registered and cross-section were assessed for qualitative (graininess, sharpness, overall image quality) and quantitative [image noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR)] image quality parameters. Image noise and signal were measured in the aortic root and the left main coronary artery, respectively. Graininess, sharpness, and overall image quality was assessed on a 4-point Likert scale.

RESULTS

As compared to FBP, ASIR, and MBAF2, ASIR + MBAF2 resulted in reduced image noise [53.1 ± 12.3, 30.6 ± 8.5, 36.3 ± 4.2, 26.3 ± 4.0 Hounsfield units (HU), respectively; p < 0.001], improved SNR (8.4 ± 2.6, 14.1 ± 3.6, 11.8 ± 2.3, 16.3 ± 3.3 HU, respectively; p < 0.001) and CNR (9.4 ± 2.7, 15.9 ± 4.0, 13.3 ± 2.5, 18.3 ± 3.5 HU, respectively; p < 0.001). No difference in sharpness was observed amongst the reconstructions (p = 0.08). Although ASIR + MBAF2 was non-superior to ASIR regarding overall image quality (p = 0.99), it performed better than FBP (p < 0.001) and MBAF2 (p < 0.001) alone.

CONCLUSION

The combination of ASIR and MBAF2 resulted in reduced image noise and improved SNR and CNR. The implementation of MBAF2 in clinical practice may result in improved noise reduction performance and could potentiate radiation dose reduction.

Image Quality Assessment of Low-Dose CT using Hybrid Iterative Reconstruction

Abstract Background: X-ray computed tomography is the first imaging technology that supports accurate nondestructive interior image reconstruction of an object from sufficient projection data. Low-dose computed tomography (LDCT) has been considered to relieve the harm to patients caused by X-ray radiation. However, LDCT images can be degraded by quantum noise and streak artifacts.Methods: The objective of the authors’ study is to evaluate the optimal level of the hybrid iterative reconstruction (HIR) that generates images with the best diagnostic quality on different dose and noise levels. HIR with optimizations is proposed to reduce image noise and provide better performance at a low dose. The Catphan®504 phantom is employed to assess various image qualities (IQ).Results: For any given scanning protocols, there is linear noise reduction and linear increase of contrast-to-noise ratio (CNR) using optimal HIR. The evidence from various module tests demonstrates that the shape of the noise power spectrum is continuously shifted to low frequency with increasing HIR levels compared with that of filtered-back-projection (FBP). This may describe the difference between the human observer performance and features of the ideal low-contrast objects.Conclusion: Optimal HIR is clearly demonstrated to be a superior method for reducing image noise and improving CNR compared to FBP. Optimal HIR also inhibits texture change or spectrum shift compared with the pure IR method. Even though there are continuous noise reduction and CNR increase with HIR at increasing levels, the human observer performance does not seem to improve simultaneously due to coarser noise (low-frequency noise). HIR level 3 to 5 is optimal for their study. It is possible for the optimal HIR to offer equivalent diagnostic IQ at a lower dose compared with FBP at a routine dose.

Automatic projection image registration for nanoscale X-ray tomographic reconstruction

Novel developments in X-ray sources, optics and detectors have significantly advanced the capability of X-ray microscopy at the nanoscale. Depending on the imaging modality and the photon energy, state-of-the-art X-ray microscopes are routinely operated at a spatial resolution of tens of nanometres for hard X-rays or ∼10 nm for soft X-rays. The improvement in spatial resolution, however, has led to challenges in the tomographic reconstruction due to the fact that the imperfections of the mechanical system become clearly detectable in the projection images. Without proper registration of the projection images, a severe point spread function will be introduced into the tomographic reconstructions, causing the reduction of the three-dimensional (3D) spatial resolution as well as the enhancement of image artifacts. Here the development of a method that iteratively performs registration of the experimentally measured projection images to those that are numerically calculated by reprojecting the 3D matrix in the corresponding viewing angles is shown. Multiple algorithms are implemented to conduct the registration, which corrects the translational and/or the rotational errors. A sequence that offers a superior performance is presented and discussed. Going beyond the visual assessment of the reconstruction results, the morphological quantification of a battery electrode particle that has gone through substantial cycling is investigated. The results show that the presented method has led to a better quality tomographic reconstruction, which, subsequently, promotes the fidelity in the quantification of the sample morphology.

Performance of Half-dose Chest Computed Tomography in Lung Malignancy Using an Iterative Reconstruction Technique

Objectives The purpose of this study was to evaluate the performance of half-dose chest CT using an iterative reconstruction technique in patients with lung malignancies. Methods The Dual-source CT scans were obtained and half-dose datasets were reconstructed with 5 different strengths in 38 adults with lung malignancies. Two radiologists graded subjective image quality; noise, contrast and sharpness at the central/peripheral lung, mediastinum and chest wall of the reconstructed half-dose images, compared with those of standard-dose images, using a three-point scale. A lesion assessment; lesion conspicuity and diagnostic confidence, was also performed. The quantitative image noises; contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were measured and compared with those of standard-dose images. Results The subjective image noise in the half-dose images was less than that of the standard-dose images. The contrast in strengths 2 to 5 was superior, the sharpness of the lung parenchyma in strengths 3 to 5 was inferior, and the CNR/SNR in all strengths were higher than those of standard-dose images ( P &lt; 0.05). The improvement of subjective image noise and contrast, the decrease in sharpness, were correlated with strength level ( P &lt; 0.05). The lesion conspicuity in half-dose images of strengths 4 and 5 was decreased. The diagnostic confidence of the half-dose images of all strengths was comparable to that of the standard-dose images ( P &lt; 0.05). Conclusions Half-dose chest CT images using an iterative reconstruction technique show decreased image noise, increased contrast, and diagnostic confidence comparable to standard-dose images. Images reconstructed with strength 2 and 3 appear to be the optimal choice in clinical practice.

A modified discrete algebraic reconstruction technique for multiple grey image reconstruction for limited angle range tomography

The `missing wedge', which is due to a restricted rotation range, is a major challenge for quantitative analysis of an object using tomography. With prior knowledge of the grey levels, the discrete algebraic reconstruction technique (DART) is able to reconstruct objects accurately with projections in a limited angle range. However, the quality of the reconstructions declines as the number of grey levels increases. In this paper, a modified DART (MDART) was proposed, in which each independent region of homogeneous material was chosen as a research object, instead of the grey values. The grey values of each discrete region were estimated according to the solution of the linear projection equations. The iterative process of boundary pixels updating and correcting the grey values of each region was executed alternately. Simulation experiments of binary phantoms as well as multiple grey phantoms show that MDART is capable of achieving high-quality reconstructions with projections in a limited angle range. The interesting advancement of MDART is that neither prior knowledge of the grey values nor the number of grey levels is necessary.

Preliminary study of dose reduction and image quality of adult pelvic low-dose CT scan with adaptive statistical iterative reconstruction

BACKGROUND

Because pelvic computed tomography (CT) is widely used in clinical practice, there are increasing concerns regarding the associated risks of radiation-induced cancer. Therefore, the capability to reduce the CT radiation dose without compromising image quality is desirable.

PURPOSE

To assess the radiation dose and image quality of adult pelvic CT using both a routine dose and low radiation dose with filtered back projection (FBP) and adaptive statistical iterative reconstruction (ASIR).

MATERIAL AND METHODS

Forty-five patients underwent both routine-dose CT with FBP reconstruction and low-dose CT with FBP and 50% ASIR blending ratio (ASIR50) reconstruction, respectively. Three different groups of image data were compared for subjective and objective image quality. CT dose index volume (CTDIvol), dose-length product (DLP), and effective dose (ED) were recorded.

RESULTS

The resulting CTDIvol, DLP, and ED following low-dose pelvic CT were 10.80 ± 6.0 mGy, 265.0 ± 55.0 mGy.Cm, and 3.97 ± 0.82 mSv, respectively. When compared with the values obtained following routine-dose pelvic CT, the low-dose pelvic CT values decreased by 62%, 55%, and 56%, respectively (P < 0.001). The results following evaluation of subjective and objective image quality revealed that there was no significant difference (P > 0.05) between routine-dose CT with FBP, and low-dose CT with ASIR50. However, significant differences were detected between low-dose CT with FBP, routine-dose CT with FBP, and low-dose CT with ASIR50 (P < 0.01).

CONCLUSION

The application of low-dose pelvic CT with ASIR50 could dramatically reduce the radiation dose and substantially improve image quality.

Explicit Filtering Based Low-Dose Differential Phase Reconstruction Algorithm with the Grating Interferometry

X-ray grating interferometry offers a novel framework for the study of weakly absorbing samples. Three kinds of information, that is, the attenuation, differential phase contrast (DPC), and dark-field images, can be obtained after a single scanning, providing additional and complementary information to the conventional attenuation image. Phase shifts of X-rays are measured by the DPC method; hence, DPC-CT reconstructs refraction indexes rather than attenuation coefficients. In this work, we propose an explicit filtering based low-dose differential phase reconstruction algorithm, which enables reconstruction from reduced scanning without artifacts. The algorithm adopts a differential algebraic reconstruction technique (DART) with the explicit filtering based sparse regularization rather than the commonly used total variation (TV) method. Both the numerical simulation and the biological sample experiment demonstrate the feasibility of the proposed algorithm.

Life and death of a single catalytic cracking particle

Fluid catalytic cracking (FCC) particles account for 40 to 45% of worldwide gasoline production. The hierarchical complex particle pore structure allows access of long-chain feedstock molecules into active catalyst domains where they are cracked into smaller, more valuable hydrocarbon products (for example, gasoline). In this process, metal deposition and intrusion is a major cause for irreversible catalyst deactivation and shifts in product distribution. We used x-ray nanotomography of industrial FCC particles at differing degrees of deactivation to quantify changes in single-particle macroporosity and pore connectivity, correlated to iron and nickel deposition. Our study reveals that these metals are incorporated almost exclusively in near-surface regions, severely limiting macropore accessibility as metal concentrations increase. Because macropore channels are "highways" of the pore network, blocking them prevents feedstock molecules from reaching the catalytically active domains. Consequently, metal deposition reduces conversion with time on stream because the internal pore volume, although itself unobstructed, becomes largely inaccessible.

Low concentration contrast medium for dual-source computed tomography coronary angiography by a combination of iterative reconstruction and low-tube-voltage technique: feasibility study

OBJECTIVES

To assess the impact of low-concentration contrast medium on vascular enhancement, image quality and radiation dose of coronary CT angiography (cCTA) by using a combination of iterative reconstruction (IR) and low-tube-voltage technique.

MATERIALS AND METHODS

One hundred patients were prospectively randomized to two types of contrast medium and underwent prospective electrocardiogram-triggering cCTA (Definition Flash, Siemens Healthcare; collimation: 128 mm × 0.6mm; tube current: 300 mAs). Fifty patients received Iopromide 370 were scanned using the conventional tube setting (100 kVp or 120 kVp if BMI ≥ 25 kg/m(2)) and reconstructed with filtered back projection (FBP). Fifty patients received Iodixanol 270 were scanned using the low-tube-voltage (80 kVp or 100 kVp if BMI ≥ 25 kg/m(2)) technique and reconstructed with IR. CT attenuation was measured in coronary artery and other anatomical regions. Noise, image quality and radiation dose were compared.

RESULTS

Compared with two Iopromide 370 subgroups, Iomeprol 270 subgroups showed no significant difference in CT attenuation (576.63 ± 95.50 vs. 569.51 ± 118.93 for BMI< 25 kg/m(2), p=0.647 and 394.19 ± 68.09 vs. 383.72 ± 63.11 for BMI ≥ 25 kg/m(2), p=0.212), noise (in various anatomical regions of interest) and image quality (3.5 vs. 4.0, p=0.13), but significantly (0.41 ± 0.17 vs. 0.94 ± 0.45 for BMI< 25 kg/m(2), p<0.001 and 1.14 ± 0.24 vs. 2.37 ± 0.69 for BMI ≥ 25 kg/m(2), p<0.001) lower radiation dose, which reflects dose saving of 56.4% and 51.9%, respectively.

CONCLUSIONS

Combined IR with low-tube-voltage technique, a low-concentration contrast medium of 270 mg I/ml can still maintain the contrast enhancement without impairing image quality, as well as significantly lower the radiation dose.

Hard X-ray spectroscopic nano-imaging of hierarchical functional materials at work

Heterogeneous catalysts often consist of an active metal (oxide) in close contact with a support material and various promoter elements. Although macroscopic properties, such as activity, selectivity and stability, can be assessed with catalyst performance testing, the development of relevant, preferably quantitative structure-performance relationships require the use of advanced characterisation methods. Spectroscopic imaging in the hard X-ray region with nanometer-scale resolution has very recently emerged as a powerful approach to elucidate the hierarchical structure and related chemistry of catalytic solids in action under realistic reaction conditions. This X-ray-based chemical imaging method benefits from the combination of high resolution (∼30 nm) with large X-ray penetration and depth of focus, and the possibility for probing large areas with mosaic imaging. These capabilities make it possible to obtain spatial and temporal information on chemical changes in catalytic solids as well as a wide variety of other functional materials, such as fuel cells and batteries, in their full complexity and integrity. In this concept article we provide details on the method and setup of full-field hard X-ray spectroscopic imaging, illustrate its potential for spatiotemporal chemical imaging by making use of recent showcases, outline the pros and cons of this experimental approach and discuss some future directions for hierarchical functional materials research.

Nondestructive volumetric 3-D chemical mapping of nickel-sulfur compounds at the nanoscale

Nano-structures of nickel (Ni) and nickel subsulfide (Ni(3)S(2)) materials were studied and mapped in 3D with high-resolution x-ray nanotomography combined with full field XANES spectroscopy. This method for characterizing these phases in complex microstructures is an important new analytical imaging technique, applicable to a wide range of nanoscale and mesoscale electrochemical systems.

TXM-Wizard: a program for advanced data collection and evaluation in full-field transmission X-ray microscopy

Transmission X-ray microscopy (TXM) has been well recognized as a powerful tool for non-destructive investigation of the three-dimensional inner structure of a sample with spatial resolution down to a few tens of nanometers, especially when combined with synchrotron radiation sources. Recent developments of this technique have presented a need for new tools for both system control and data analysis. Here a software package developed in MATLAB for script command generation and analysis of TXM data is presented. The first toolkit, the script generator, allows automating complex experimental tasks which involve up to several thousand motor movements. The second package was designed to accomplish computationally intense tasks such as data processing of mosaic and mosaic tomography datasets; dual-energy contrast imaging, where data are recorded above and below a specific X-ray absorption edge; and TXM X-ray absorption near-edge structure imaging datasets. Furthermore, analytical and iterative tomography reconstruction algorithms were implemented. The compiled software package is freely available.

The effect of adaptive iterative dose reduction on image quality in 320-detector row CT coronary angiography

OBJECTIVE

To evaluate the effect of adaptive iterative dose reduction (AIDR) on image noise and image quality as compared with standard filtered back projection (FBP) in 320-detector row CT coronary angiography (CTCA).

METHODS

50 patients (14 females, mean age 68 ± 9 years) who underwent CTCA (100 kV or 120 kV, 400-580 mA) within a single heartbeat were enrolled. Studies were reconstructed with FBP and subsequently AIDR. Image noise, vessel contrast and contrast-to-noise ratio (CNR) in the coronary arteries were evaluated. Overall image quality for coronary arteries was assessed using a five-point scale (1, non-diagnostic; 5, excellent).

RESULTS

All the examinations were performed in a single heartbeat. Image noise in the aorta was significantly lower in data sets reconstructed with AIDR than in those reconstructed with FBP (21.4 ± 3.1 HU vs 36.9 ± 4.5 HU; p<0.001). No significant differences were observed between FBP and AIDR for the mean vessel contrast (HU) in the proximal coronary arteries. Consequently, CNRs in the proximal coronary arteries were higher in the AIDR group than in the FBP group (p<0.001). The mean image quality score was improved by AIDR (3.75 ± 0.38 vs 4.24 ± 0.38; p<0.001).

CONCLUSION

The use of AIDR reduces image noise and improves image quality in 320-detector row CTCA.

Three-dimensional imaging of chemical phase transformations at the nanoscale with full-field transmission X-ray microscopy

The ability to probe morphology and phase distribution in complex systems at multiple length scales unravels the interplay of nano- and micrometer-scale factors at the origin of macroscopic behavior. While different electron- and X-ray-based imaging techniques can be combined with spectroscopy at high resolutions, owing to experimental time limitations the resulting fields of view are too small to be representative of a composite sample. Here a new X-ray imaging set-up is proposed, combining full-field transmission X-ray microscopy (TXM) with X-ray absorption near-edge structure (XANES) spectroscopy to follow two-dimensional and three-dimensional morphological and chemical changes in large volumes at high resolution (tens of nanometers). TXM XANES imaging offers chemical speciation at the nanoscale in thick samples (>20 µm) with minimal preparation requirements. Further, its high throughput allows the analysis of large areas (up to millimeters) in minutes to a few hours. Proof of concept is provided using battery electrodes, although its versatility will lead to impact in a number of diverse research fields.

Phase retrieval using polychromatic illumination for transmission X-ray microscopy

An alternative method for quantitative phase retrieval in a transmission X-ray microscope system at sub-50-nm resolution is presented. As an alternative to moving the sample in the beam direction in order to analyze the propagation-introduced phase effect, we have illuminated the TXM using X-rays of different energy without any motor movement in the TXM system. Both theoretical analysis and experimental studies have confirmed the feasibility and the advantage of our method, because energy tuning can be performed with very high energy resolution using a double crystal monochromator at a synchrotron beam line, and there is zero motor error in TXM system in our approach. High-spatial-resolution phase retrieval is accomplished using the proposed method.

Phase retrieval using polychromatic illumination for transmission X-ray microscopy

An alternative method for quantitative phase retrieval in a transmission X-ray microscope system at sub-50-nm resolution is presented. As an alternative to moving the sample in the beam direction in order to analyze the propagation-introduced phase effect, we have illuminated the TXM using X-rays of different energy without any motor movement in the TXM system. Both theoretical analysis and experimental studies have confirmed the feasibility and the advantage of our method, because energy tuning can be performed with very high energy resolution using a double crystal monochromator at a synchrotron beam line, and there is zero motor error in TXM system in our approach. High-spatial-resolution phase retrieval is accomplished using the proposed method.

A prospective evaluation of dose reduction and image quality in chest CT using adaptive statistical iterative reconstruction

OBJECTIVE

The purpose of this study was to compare the subjective image quality, image noise, and radiation dose of chest CT images reconstructed with a 30% blend of iterative reconstruction and 70% conventional filtered back projection (FBP) with those of images generated with 100% FBP.

SUBJECTS AND METHODS

Clinically indicated chest CT examinations of 292 consecutively registered patients were prospectively alternately assigned to two scanners on which different reconstruction techniques were used: adaptive statistical iterative reconstruction (ASIR) blended with FBP and 100% FBP. Both acquisitions were performed with dose modulation (noise index, 25 for ASIR and 21 for FBP). Patient demographics and habitus were recorded. Two radiologists blinded to the reconstruction algorithm independently scored subjective image quality on a 3-point Likert scale and measured image noise and radiation dose.

RESULTS

Compared with FBP images, ASIR images had significantly lower subjective image quality (p = 0.01), less image noise (p = 0.02), and less radiation dose (p < 0.0001). The CT dose index of the ASIR cohort (11.3 ± 51) was significantly lower than that of the 100% FBP cohort (15.4 ± 6.3) (p < 0.0001). Interobserver agreement on subjective image quality was excellent for both ASIR and FBP (Cronbach α, 0.92, p < 0.0001; Cronbach α, 0.85, p < 0.0001).

CONCLUSION

In clinically indicated chest CT examinations, ASIR images had better image quality and less image noise at a lower radiation dose than images acquired with a conventional FBP reconstruction algorithm.

Estimated radiation dose reduction using adaptive statistical iterative reconstruction in coronary CT angiography: the ERASIR study

OBJECTIVE

The objective of our study was to assess the impact of Adaptive Statistical Iterative Reconstruction (ASIR) on radiation dose and study quality for coronary CT angiography (CTA).

SUBJECTS AND METHODS

We prospectively evaluated 574 consecutive patients undergoing coronary CTA at three centers. Comparisons were performed between consecutive groups initially using filtered back projection (FBP) (n = 331) and subsequently ASIR (n = 243) with regard to patient and scan characteristics, radiation dose, and diagnostic study quality.

RESULTS

There was no difference between groups in the use of prospective gating, tube voltage, or scan length. The examinations performed using ASIR had a lower median tube current than those obtained using FBP (median [interquartile range], 450 mA [350-600] vs 650 mA [531-750], respectively; p < 0.001). There was a 44% reduction in the median radiation dose between the FBP and ASIR cohorts (4.1 mSv [2.3-5.2] vs 2.3 mSv [1.9-3.5]; p < 0.001). After adjustment for scan settings, ASIR was associated with a 27% reduction in radiation dose compared with FBP (95% CI, 21-32%; p < 0.001). Despite the reduced current, ASIR was not associated with a difference in adjusted signal, noise, or signal-to-noise ratio (p = not significant). No differences existed between FBP and ASIR for interpretability per coronary artery (98.5% vs 99.3%, respectively; p = 0.12) or per patient (96.1% vs 97.1%, p = 0.65). CONCLUSION. ASIR enabled reduced tube current and lower radiation dose in comparison with FBP, with preserved signal, noise, and study interpretability, in a large multicenter cohort. ASIR represents a new technique to reduce radiation dose in coronary CTA studies.

Adaptive statistical iterative reconstruction: assessment of image noise and image quality in coronary CT angiography

OBJECTIVE

The purpose of our study was to determine the effect of Adaptive Statistical Iterative Reconstruction (ASIR) on cardiac CT angiography (CTA) signal, noise, and image quality.

MATERIALS AND METHODS

We evaluated 62 consecutive patients at three sites who underwent clinically indicated cardiac CTA using an ASIR-capable 64-MDCT scanner and a low-dose cardiac CTA technique. Studies were reconstructed using filtered back projection (FBP), ASIR-FBP composites using 20-80% ASIR, and 100% ASIR. The signal and noise were measured in the aortic root and each of the four coronary arteries. Two blinded readers graded image quality on a 5-point Likert scale and determined the proportion of interpretable segments. All segments were included for analysis regardless of size.

RESULTS

In comparison with FBP (0% ASIR), the use of 20%, 40%, 60%, 80%, and 100% ASIR resulted in reduced image noise between groups (-7%, -17%, -26%, -35%, and -43%, respectively; p < 0.001) without difference in signal (p = 0.60). There were significant differences between groups (0%, 20%, 40%, 60%, 80%, and 100% ASIR) in the Likert scores (1.5, 2.1, 3.7, 3.8, 2.0, and 1.1, respectively; p < 0.001) and proportion of interpretable segments (88.7%, 89.3%, 90.5%, 90.4%, 88.0%, and 87.3%, respectively; p < 0.001). Reconstruction using 40% and 60% ASIR had the highest Likert scores and largest proportion of interpretable segments. In comparison with FBP, each was associated with higher Likert scores and increased interpretable segments (p < 0.001 for all).

CONCLUSION

ASIR resulted in noise reduction and significantly impacted image quality. When using a low tube current technique, cardiac CTA reconstruction using 40% or 60% ASIR significantly improved image quality and the proportion of interpretable segments compared with FBP reconstruction.

Transmission X-ray microscopy for full-field nano imaging of biomaterials

Imaging of cellular structure and extended tissue in biological materials requires nanometer resolution and good sample penetration, which can be provided by current full-field transmission X-ray microscopic techniques in the soft and hard X-ray regions. The various capabilities of full-field transmission X-ray microscopy (TXM) include 3D tomography, Zernike phase contrast, quantification of absorption, and chemical identification via X-ray fluorescence and X-ray absorption near edge structure imaging. These techniques are discussed and compared in light of results from the imaging of biological materials including microorganisms, bone and mineralized tissue, and plants, with a focus on hard X-ray TXM at ≤ 40-nm resolution.

Low-dose, simple, and fast grating-based X-ray phase-contrast imaging

Phase sensitive X-ray imaging methods can provide substantially increased contrast over conventional absorption-based imaging and therefore new and otherwise inaccessible information. The use of gratings as optical elements in hard X-ray phase imaging overcomes some of the problems that have impaired the wider use of phase contrast in X-ray radiography and tomography. So far, to separate the phase information from other contributions detected with a grating interferometer, a phase-stepping approach has been considered, which implies the acquisition of multiple radiographic projections. Here we present an innovative, highly sensitive X-ray tomographic phase-contrast imaging approach based on grating interferometry, which extracts the phase-contrast signal without the need of phase stepping. Compared to the existing phase-stepping approach, the main advantages of this new method dubbed "reverse projection" are not only the significantly reduced delivered dose, without the degradation of the image quality, but also the much higher efficiency. The new technique sets the prerequisites for future fast and low-dose phase-contrast imaging methods, fundamental for imaging biological specimens and in vivo studies.