Application of X-ray grating interferometry for the imaging of joint structures

Grating-based x-ray phase-contrast imaging is a fast developing new modality not only for medical imaging, but as well for other fields such as material sciences. While these many possible applications arise, the knowledge of the noise behavior is essential. In this work, the authors used a least squares fitting algorithm to calculate the noise behavior of the three quantities absorption, differential phase, and dark-field image. Further, the calculated error formula of the differential phase image was verified by measurements. Therefore, a Talbot interferometer was setup, using a microfocus x-ray tube as source and a Timepix detector for photon counting. Additionally, simulations regarding this topic were performed. It turned out that the variance of the reconstructed phase is only dependent of the total number of photons used to generate the phase image and the visibility of the experimental setup. These results could be evaluated in measurements as well as in simulations. Furthermore, the correlation between absorption and dark-field image was calculated. These results provide the understanding of the noise characteristics of grating-based phase-contrast imaging and will help to improve image quality.

Extraction of phase and amplitude information in differential interference contrast (DIC) microscopy is a challenging but stimulating task. In this paper, a simple straightforward non‐iterative method to extract the absorption and phase difference images for DIC is presented. According to the method proposed in [1], phase information can be acquired straightforwardly. The feasibility of our method is confirmed by experimental results of imaging liquid paraffin drops using a commercial DIC microscope. Compared with the available methods and previous research [1–4], our approach simplifies the procedures to extract the absorption and phase difference images without weak absorption limit.

Interferometric temperature measurement around an isolated boiling bubble was conducted for studying heat transfer from liquid phase to the bubble. Finite fringe interferogram was captured with Mach-Zehnder type interferometer and a high-speed camera. Brightness distribution in the interferogram was converted to series wrapped phase image and axisymmetric differential temperature image through wrapped phase image, differential phase image, unwrapped phase image, and differential refractive index image by the Hilbert transform and Abel inversion. The resulted differential temperature image shows that the superheated liquid layer on the heating surface is lifted up and stretched by the growing bubble, and that hot liquid flow is accompanied by departed bubble.

Taking advantage of the fact that an X-ray Talbot interferometer functions with X-rays of a broad energy bandwidth, high-speed X-ray phase tomography has been demonstrated by using white synchrotron light. Time resolution in addition to three-dimensional spatial resolution has been attained, and we report this achievement as the first four-dimensional (4D) X-ray phase tomography. Moire image movies of samples rotating at a speed of 1 or 2 rps generated by a Talbot interferometer were recorded at a frame rate of up to 1 kf/s, and differential phase image movies of the same frame rate were created by the Fourier-transform method. Consequently, a sub-second time resolution was achieved in the 4D phase tomography, while the spatial resolution was below 0.1 mm and 0.05 mm in axial and in-plane directions, respectively. An X-ray Talbot interferometer generates visibility images in addition to differential phase images, showing the distribution of microstructures, which cause ultra-small angle scattering but cannot be resolved individually with system spatial resolution. Tomographic image reconstruction from the visibility images was also demonstrated.

X-ray phase contrast imaging (PCI) provides excellent image contrast by utilizing the phase shift. The introduction of microbubbles into tissues can cause a phase shift to make microbubbles visibly identified on PCI. In this study, we assessed the feasibility of targeted microbubble-based PCI for the detection of thrombosis. The absorption and phase contrast images of P-selectin-targeted microbubbles (MBP) were obtained and compared in vitro. MBP, control IgG-targeted microbubbles (MBC), and unbound microbubbles (MBU) were tested for binding specificity on thrombi expressing P-selectin. MBP were used as molecular PCI probes to evaluate P-selectin expression in a mouse model of arteriovenous shunt thrombosis that was created using PE tubes in the bypass outside of the mouse body. PCI clearly showed the microbubbles not viewable via absorption contrast imaging (ACI). In vitro attachment of MBP (91.60 ± 11.63) to thrombi was significantly higher than attachment of MBC (17.80 ± 4.02, P < 0.001) or MBU (9.80 ± 2.59, P < 0.001). In the mouse model of arteriovenous shunt thrombosis, the binding affinity of MBP (15.50 ± 6.25) was significantly greater than that of MBC (0.50 ± 0.84, P < 0.001) or MBU (0.33 ± 0.52, P < 0.001). Our results indicate that molecular PCI may be considered as a novel and promising imaging modality for the investigation of thrombosis. • Small thrombi are rarely detected by conventional radiography. • Phase contrast imaging (PCI) provides higher contrast and spatial resolution than conventional radiography. • P-selectin targeted microbubbles detected by PCI may suggest early thrombosis.

Optical coherence tomography angiography (OCTA) suffers from more motion artifacts compared to optical coherence tomography, which are the primary source of image quality degradation in in vivo imaging. We propose an OCTA algorithm in this Letter that differs from motion compensation methods widely employed to reduce motion artifacts and effectively mitigates these artifacts. The algorithm integrates differential phase and intensity images based on the standard deviation of the flow signals. The performance of this algorithm is evaluated on mouse retina in vivo imaging. Compared to three conventional OCTA algorithms, the OCTA images obtained by the proposed algorithm exhibit fewer motion artifacts and less noise in tissue regions, with maximum improvements of 1.38 dB and 0.82 in signal-to-noise ratio and contrast-to-noise ratio (CNR), respectively, in the maximum projection of en face images.

We show that a distribution of micrometer-sized calcifications in the human breast which are not visible in clinical x-ray mammography at diagnostic dose levels can produce a significant dark-field signal in a grating-based x-ray phase-contrast imaging setup with a tungsten anode x-ray tube operated at 40 kVp. A breast specimen with invasive ductal carcinoma was investigated immediately after surgery by Talbot–Lau x-ray interferometry with a design energy of 25 keV. The sample contained two tumors which were visible in ultrasound and contrast-agent enhanced MRI but invisible in clinical x-ray mammography, in specimen radiography and in the attenuation images obtained with the Talbot–Lau interferometer. One of the tumors produced significant dark-field contrast with an exposure of 0.85 mGy air-kerma. Staining of histological slices revealed sparsely distributed grains of calcium phosphate with sizes varying between 1 and 40 μm in the region of this tumor. By combining the histological investigations with an x-ray wave-field simulation we demonstrate that a corresponding distribution of grains of calcium phosphate in the form of hydroxylapatite has the ability to produce a dark-field signal which would—to a substantial degree—explain the measured dark-field image. Thus we have found the appearance of new information (compared to attenuation and differential phase images) in the dark-field image. The second tumor in the same sample did not contain a significant fraction of these very fine calcification grains and was invisible in the dark-field image. We conclude that some tumors which are invisible in x-ray absorption mammography might be detected in the x-ray dark-field image at tolerable dose levels.

A novel information retrieval algorithm for X-ray grating-based phase-contrast imaging based on the deconvolution of the object and the reference phase stepping curve (PSC) as proposed by Modregger et al. was investigated in this paper. We applied the method for the first time on data obtained with a polychromatic spectrum and compared the results to those, received by applying the commonly used method, based on a Fourier analysis. We confirmed the expectation, that both methods deliver the same results for the absorption and the differential phase image. For the darkfield image, a mean contrast-to-noise ratio (CNR) increase by a factor of 1.17 using the new method was found. Furthermore, the dose saving potential was estimated for the deconvolution method experimentally. It is found, that for the conventional method a dose which is higher by a factor of 1.66 is needed to obtain a similar CNR value compared to the novel method. A further analysis of the data revealed, that the improvement in CNR and dose efficiency is due to the superior background noise properties of the deconvolution method, but at the cost of comparability between measurements at different applied dose values, as the mean value becomes dependent on the photon statistics used.

Electron differential microscopy using an electron trapezoidal prism

Introduction: In today's orthopaedic practice, meniscus and anterior cruciate ligament (ACL) injuries are prevalent. It is more common in sports injuries and automobile accidents. In patients with ACL tears, meniscus problems are also common. Several studies have linked meniscus injuries to the development of osteoarthritis in early stages. Early onset of osteoarthritis has been observed in ACL-repaired patients with meniscus tears. As a result, meniscus tears should be detected and corrected as soon as possible to avoid degenerative changes in the knee joint. The goal of the study was to see if there was a link between meniscus injuries and ACL injuries in our rural community.Methods: This retrospective study was conducted on 48 patients at the R.L. Jalappa Hospital & Research Centre from January 2012 to December 2019. Patients between the ages of 18-65 diagnosed with ACL tear with/without meniscus damage in their knees were included in the study. Patients with posterior cruciate ligament (PCL) tear, medial collateral ligament (MCL) or lateral collateral ligament (LCL) injury, previously operated index knees, and patients with more than grade 3 knee osteoarthritis (Kellgren and Lawrence classification) were excluded. Clinical assessment of patients with knee injuries, MRI and diagnostic arthroscopy of the knee joint details were collected. After obtaining the data, we estimated the incidence of meniscus injuries associated with chronic ACL injuries. We also calculated the percentage of side/laterality injury (medial meniscus or lateral meniscus) and part of meniscus injury (anterior horn, body, and posterior horn) in chronic ACL-deficient knees. Patient characteristics such as age and gender were correlated with functional knee assessment using a modified Lysholm score. P-value and chi-square tests were used to assess the data. P-value of less than 0.5 was considered significant.Results: Average age of the participants was 32.31 years. There were 42 men and six women in the group. Isolated medial meniscus, lateral meniscus, and combined medial and lateral meniscus had average ages of 31.83, 31.16, and 40.28 years, respectively. ACL injuries on the right side were seen in 23 patients the left side was seen in 25 patients. In comparison to the right side, the isolated medial meniscus injury on the left side was more severe. In case of a combination of medial and lateral meniscus tears, the right side suffered more damage than the left. Eleven patients had an isolated ACL tear without a meniscus injury, while the other 37 had a meniscus injury and an ACL tear. Excellent scores were observed in 11 cases, satisfactory scores in 26, and unsatisfactory in 11 cases. Age group was categorized into three groups, less than 30, 30-45, and more than 45 years. Excellent, satisfactory, and unsatisfactory scores were observed in seven, eleven, and seven patients on the left side and excellent, satisfactory, and unsatisfactory scores in four, fifteen, and four patients on the right side, respectively. P-value was not statistically significant when comparing outcomes by age, gender, or side.Conclusion: Meniscus injuries occurred 77% of the time when there was a persistent ACL injury. In comparison to a lateral meniscus injury, the incidence of medial meniscus injury associated with chronic ACL tear was higher. In comparison to the anterior horn and body of the medial meniscus, the majority of medial meniscus tears were found in the posterior horn.

Phase retrieval for X-ray differential phase contrast radiography with knowledge transfer learning from virtual differential absorption model

We are attempting to expand the technology of X-ray grating phase imaging/tomography to enable dynamic observation. X-ray phase imaging has been performed mainly for static cases, and this challenge is significant since properties of materials (and hopefully their functions) would be understood by observing their dynamics in addition to their structure, which is an inherent advantage of X-ray imaging. Our recent activities in combination with white synchrotron radiation for this purpose are described. Taking advantage of the fact that an X-ray grating interferometer functions with X-rays of a broad energy bandwidth (and therefore high flux), movies of differential phase images and visibility images are obtained with a time resolution of a millisecond. The time resolution of X-ray phase tomography can therefore be a second. This study is performed as a part of a project to explore X-ray grating interferometry, and our other current activities are also briefly outlined.

We demonstrate volumetric phase contrast imaging by using optical coherence tomography (OCT). In general, the randomness of the scatterers’ distribution prohibits the volumetric measurement of a meaningful phase in a scattering mode. Our method uses complex numerical manipulation of an en-face complex OCT and gives a transversally differential phase image similar to a differential interference contrast microscope (DIC). Not like the DIC, our method can arbitrarily select the amount and direction of the shear after the OCT acquisition. In addition it provides DIC-like images at arbitrary depths. This method is validated by using a 840-nm spectral domain OCT system. A zebrafish sample is measured over a 1-mm × 1-mm transversal scanning range.

Scanning hard X-ray nanoprobe imaging provides a unique tool for probing specimens with high sensitivity and large penetration depth. Moreover, the combination of complementary techniques such as X-ray fluorescence, absorption, phase contrast and dark field imaging gives complete quantitative information on the sample structure, composition and chemistry. The multi-technique “FLYSCAN” data acquisition scheme developed at Synchrotron SOLEIL permits to perform fast continuous scanning imaging and as such makes scanning tomography techniques feasible in a time-frame well-adapted to typical user experiments. Here we present the recent results of simultaneous fast scanning multi-technique tomography performed at Soleil. This fast scanning scheme will be implemented at the Nanoscopium beamline for large field of view 2D and 3D multimodal imaging.

In propagation-based X-ray phase-contrast (PB XPC) imaging, the measured image contains a mixture of absorption- and phase-contrast. To obtain separate images of the projected absorption and phase (i.e., refractive) properties of a sample, phase retrieval methods can be employed. It has been suggested that phase-retrieval can always improve image quality in PB XPC imaging. However, when objective (task-based) measures of image quality are employed, this is not necessarily true and phase retrieval can be detrimental. In this work, signal detection theory is utilized to quantify the performance of a Hotelling observer (HO) for detecting a known signal in a known background. Two cases are considered. In the first case, the HO acts directly on the measured intensity data. In the second case, the HO acts on either the retrieved phase or absorption image. We demonstrate that the performance of the HO is superior when acting on the measured intensity data. The loss of task-specific information induced by phase-retrieval is quantified by computing the efficiency of the HO as the ratio of the test statistic signal-to-noise ratio (SNR) for the two cases. The effect of the system geometry on this efficiency is systematically investigated. Our findings confirm that phase-retrieval can impair signal detection performance in XPC imaging.