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(a-c) Schematic diagrams of the synchrotron and (d) laboratory implementations of the EI system. An x-ray beam aligned with the edge of a pixel (a) is refracted away (b) or toward (c) the pixel after passing through an object. In the laboratory, (d) two masks are employed to replicate the EI condition over the entire field of view.
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Edge illumination (EI) is an x-ray phase-contrast imaging technique, exploiting sensitivity to x-ray refraction to visualize features, which are often not detected by conventional absorption-based radiography. The method does not require a high degree of spatial coherence and is achromatic and, therefore, can be implemented with both synchrotron ra...
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... pixel row or column, such that only part of the beam reaches the pixels. When an object is placed in the beam path, any refraction caused by the object will lead to a change in detected intensity, as it would deflect the beam toward or away from the pixel. In this example, upward refraction will lead to a decrease in measured intensity [see Fig. 1(b)] while refraction downward will increase the detected intensity [see Fig. 1(c)]. Practically, at a synchrotron, the incoming beam is collimated by a vertically narrow and horizontally long slit placed upstream of the object while an absorbing edge is placed in contact with the detector row to create the EI condition. Therefore, in this ...
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... When an object is placed in the beam path, any refraction caused by the object will lead to a change in detected intensity, as it would deflect the beam toward or away from the pixel. In this example, upward refraction will lead to a decrease in measured intensity [see Fig. 1(b)] while refraction downward will increase the detected intensity [see Fig. 1(c)]. Practically, at a synchrotron, the incoming beam is collimated by a vertically narrow and horizontally long slit placed upstream of the object while an absorbing edge is placed in contact with the detector row to create the EI condition. Therefore, in this configuration, to obtain an image of the entire object, the latter must be ...
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... translation to a laboratory environment (using a polychromatic and extended source). 13 To enable area imaging and avoid scan- ning the object (which would lead to impractical scan times when using a commercial source), the slit and edge are replaced with two masks, which replicate the EI condition for all detector rows (or columns), as shown in Fig. 1(d). The first mask (sample mask) is placed upstream of the object and divides the incoming beam into physically separated beamlets. The second mask (detector mask) is placed in contact with the detector and creates insensitive regions between pixels. The detector mask is fabricated with a period matching the detector pixel size while the ...
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Citations
... Among the emerging XPCI techniques, edge illumination (EI) is particularly suitable for use with lab-based X-ray sources that have a large focal spot and a polychromatic spectrum [2,12]. In this technique, the phase information can be retrieved by displacing two strongly absorbing masks relative to each other, with the object positioned in between. ...
Edge illumination (EI) is an X-ray imaging technique that, in addition to conventional absorption contrast, provides refraction and scatter contrast. It relies on an absorption mask in front of the sample that splits the X-ray beam into beamlets, which hits a second absorption mask positioned in front of the detector. The sample mask is then shifted in multiple steps with respect to the detector mask, thereby measuring an illumination curve per detector element. The width, position, and area of this curve estimated with and without the sample in the beam is then compared, which ultimately provides absorption, refraction, and scatter contrast for each detector pixel. From the obtained contrast sinograms, three contrast tomograms can be computed. In summary, conventional EI relies on a two-stage process comprised of a computational and time intensive contrast retrieval process, followed by tomographic reconstruction. In this work, a novel joint reconstruction method is proposed, which utilizes a combined forward model to reconstruct the three contrasts simultaneously, without the need for an intermediate contrast retrieval step. Compared to the state-of-the-art, this approach reduces reconstruction times, as the retrieval step is skipped and allows a much more flexible acquisition scheme, as there is no need to sample a full illumination curve at each projection angle. The proposed method is shown to improve reconstruction quality on subsampled datasets, enabling the reconstruction of three contrasts from single-shot datasets.
... 10,11 Edge illumination (EI) is an emerging XPCI technique, well-suited for use with lab-based X-ray sources with a large focal spot and polychromatic spectrum. 2,12 The phase information can be retrieved by displacing two strongly attenuating masks relative to each other with the object positioned in between. Traditionally, multiple images at a single view angle are taken, one for each mask displacement, after which a Gaussian is fitted to the data in each detector pixel. ...
... 3.4 d). The first slit is placed before the sample and is used to collimate the beam and a second slit is aligned with the detector so that only a single row of pixels is left uncovered (Zamir et al., 2017). Because of this configuration, to obtain the whole image it is necessary to scan the sample vertically, in the orthogonal direction with respect to the slits and then combining together the single acquisitions. ...
The aim of this PhD thesis is to develop the technic of X-ray phase imaging with Hartmann wavefront sensor for various applications and to compare this new system against well-established phase-contrast techniques. The X-ray phase imaging will be mainly performed in 3D using tomographic setup. The main application includes the study of alteractions in the central nervous system induced by neurodegenerative diseases. The first introductory section describes the basic aspects of X-ray interaction with matter and of yhe coherence theory with specific application to the Hartmann wavefront sensor design. In the second chapter, an introduction to the free-space propagation technique. The third chapter examines the principles of tomography acquisitions and the available reconstruction algorithms. A separate chapter, labeled 4, is dedicated to the theory of Hartmann wavefront sensor. A 3D wave propagation model based on Fresnel propagator was developed to optimize the architecture of the full wavefront sensor including the Hartmann plate, the distances between the different elements of the set-up as well as the X-ray source. The model can manage any degree of spatial coherence, enabling the accurate simulation of a wide range of X-ray sources. Several simulations of standard experimental situations are described to valid the program. Then, the main wavefront reconstruction algorithms have been analyzed. In chapter 5, we will present experimental results obtained with the X-ray Hartmann wavefront sensor using both a parallel beam geometry (synchrotron measurements) and a cone beam geometry (laboratory measurements). Different Hartmann plates were used with the laboratory set-up to visualize a series of test and biological samples. also, using synchrotron, we tested the Hartmann sensor to retrieve the chemical composition of objects composed of known materials. The chemical composition could be inferred starting from direct and independent measurements of the real part (proportional to the phase) and the imaginary part (proportional to the absorption) of the sample refractive index. In chapter 6, the experimental results obtained with free space propagation X-ray phase contrast tomography will be discussed. We exploited the capability of X-ray phase contrast imaging to investigate the effects of neurodegenerative diseases on the central nervous system.
... This is due to the developments and availability in micro-and nano-focus X-ray sources and X-ray optical elements such as diffraction gratings. The main techniques used for laboratory X-ray phase-contrast imaging (PCI) include grating-based PCI [10,12,13], propagation-based PCI [1,2,14], speckle-based PCI [15] and edge illumination [16]. ...
Phase-contrast, and in general, multi-modal, X-ray micro-tomography is proven to be very useful for low-density, low-attention samples enabling much better contrast than its attenuation-based pendant. Therefore, it is increasingly applied in bio- and life sciences primarily dealing with such samples. Although there is a plethora of literature regarding phase-retrieval algorithms, access to implementations of those algorithms is relatively limited and very few packages combining phase-retrieval methods with the full tomographic reconstruction pipeline are available. This is especially the case for laboratory-based phase-contrast imaging typically featuring cone-beam geometry. We present here an in-house cone-beam tomographic reconstruction package for laboratory X-ray phase-contrast imaging. It covers different phase-contrast techniques and phase retrieval methods. The paper explains their implementation and integration in the filtered back projection chain. Their functionality and efficiency will be demonstrated through applications on a few dedicated samples.
... The presence of the mask has another advantage: sensitivity to phase contrast can be achieved by adding an array of beam stops in front of the detector, in such a way that their edges partly intercept each beamlet. This transforms the scanner into an 'edge illumination' x-ray phase contrast imaging system 14,36 , where refraction of the beamlets changes the fraction of x-rays detected by each pixel. X-ray phase contrast imaging is known to provide an improved contrast-to-noise ratio (CNR) for samples that exhibit weak intrinsic x-ray attenuation, such as soft biological tissue, light plastics, or other low atomic number materials 37 . ...
In x-ray computed tomography (CT), the achievable image resolution is typically limited by several pre-fixed characteristics of the x-ray source and detector. Structuring the x-ray beam using a mask with alternating opaque and transmitting septa can overcome this limit. However, the use of a mask imposes an undersampling problem: to obtain complete datasets, significant lateral sample stepping is needed in addition to the sample rotation, resulting in high x-ray doses and long acquisition times. Cycloidal CT, an alternative scanning scheme by which the sample is rotated and translated simultaneously, can provide high aperture-driven resolution without sample stepping, resulting in a lower radiation dose and faster scans. However, cycloidal sinograms are incomplete and must be restored before tomographic images can be computed. In this work, we demonstrate that high-quality images can be reconstructed by applying the recently proposed Mixed Scale Dense (MS-D) convolutional neural network (CNN) to this task. We also propose a novel training approach by which training data are acquired as part of each scan, thus removing the need for large sets of pre-existing reference data, the acquisition of which is often not practicable or possible. We present results for both simulated datasets and real-world data, showing that the combination of cycloidal CT and machine learning-based data recovery can lead to accurate high-resolution images at a limited dose.
... As shown in Figure 5, the noise reduction ratio caused by our adaptive distributions decreases as the visibility increases, and the proposed fluence distribution is better than the original one It is obvious that there are two main parameters (the standard deviation and the mean value ) in the Gaussian model which may influence the noise performance. According to the literature, 9,26,27 the collimated beam in EI usually causes symmetrical and narrow Gaussian-shape PSCs, which means the standard deviation is small and the mean value is close to zero. ...
Purpose: X‐ray phase‐contrast imaging (XPCI) can provide multiple contrasts with great potentials for clinical and industrial applications, including conventional attenuation, phase contrast, and dark field. Grating‐based imaging (GBI) and edge‐illumination (EI) are two promising types of XPCI as the conventional x‐ray sources can be directly utilized. For the GBI and EI systems, the phase‐stepping acquisition with multiple exposures at a constant fluence is usually adopted in the literature.This work, however, attempts to challenge such a constant fluence concept during the phase‐stepping process and proposes a fluence adaptation mechanism for dose reduction.
Method: Given the importance of patient radiation dose for clinical applications, numerous studies have tried to reduce patient dose in XPCI by altering imaging system designs, data acquisition, and information retrieval. Recently, analytic multiorder moment analysis has been proposed to improve the computing efficiency. In these algorithms, multiple contrasts can be calculated by summing together the weighted phase‐stepping curves (PSCs) with some kernel functions, which suggests us that the raw data at different steps have different contributions for the noise in retrieved contrasts. Therefore, it is possible to improve the noise performance by adjusting the fluence distribution during the phase‐stepping process directly. Based on analytic retrieval formulas and the Gaussian noise model for detected signals, we derived an optimal adaptive fluence distribution, which is proportional to the absolute weighting kernel functions and the root of original sample PSCs acquired under the constant fluence. Considering that the original sample PSC might be unavailable, we proposed two practical forms for the GBI and EI systems, which are also able to reduce the contrast noise when comparing with the constant fluence distribution. Since the kernel functions are target contrast‐dependent, our proposed fluence adaptation mechanism provides a way of realizing a contrast‐based dose optimization while keeping the same noise level.
Results: To validate our analyses, simulations and experiments are conducted for the GBI and EI systems. Simulated results demonstrate that the dose reduction ratio between our proposed fluence distributions and the typical constant one can be about 20% for the phase contrast, which is consistent with our theoretical predictions. Although the experimental noise reduction ratios are a little smaller than the theoretical ones, low‐dose experiments observe better noise performance by our proposed method. Our simulated results also give out the effective ranges of the parameters of the PSCs, such as the visibility in the GBI, the standard deviation, and the mean value in the EI, providing a guidance for the use of our proposed approach in practice.
Conclusions: In this paper, we propose a fluence adaptation mechanism for contrast‐based dose optimization in XPCI, which can be applied to the GBI and EI systems. Our proposed method explores a new direction for dose reduction, and may also be further extended to other types of XPCI systems and information retrieval algorithms.
... The position of the X-ray beam on the detector shifts owing to refraction from the sample, causing an intensity change in the detector. If the beam penetrates the sample, an image showing a mixture of absorption and refraction contrasts is obtained [133][134][135][136][137]. ...
Numerous advances have been made in X-ray technology in recent years. X-ray imaging plays an important role in the nondestructive exploration of the internal structures of objects. However, the contrast of X-ray absorption images remains low, especially for materials with low atomic numbers, such as biological samples. X-ray phase-contrast images have an intrinsically higher contrast than absorption images. In this review, the principles, milestones, and recent progress of X-ray phase-contrast imaging methods are demonstrated. In addition, prospective applications are presented.
... An additional difference is that cycloidal computed tomography offers a simple solution for switching from attenuation into phase-contrast mode, allowing us to increase feature detectability when necessary, e.g., for samples that are composed of similar or low-atomic-number materials, such as soft biological tissue [17]. For example, by adding an array of beam stops in front of the detector [ Fig. 1(a)], the setup is transformed into an edgeillumination x-ray phase-contrast imaging device [18]. In such a system, the beamlets are initially aligned with the edges of the beam stops, causing a certain (reference) intensity to fall onto the pixels. ...
A general concept is presented for increasing the in-slice spatial resolution in computed tomography in a flexible manner and with relatively large source focal spots and detector pixels. The flexibility is a result of probing the sample with an array of thin beamlets shaped by a mask. Provided that the mask apertures are smaller than the combined blur of the x-ray source and detector and that no significant overlap between beamlets occurs, this introduces higher spatial frequencies into the image-formation process. The application of a cycloidal acquisition scheme, by which the sample is simultaneously rotated and translated, facilitates an efficient exploitation of these frequencies and their reconstruction into high-resolution tomographic images. Additionally, a preliminary study of the signal-to-noise ratio versus the delivered dose reveals significant dose-saving potential.
... Conventional analytic two-step reconstruction methods for EIXPCT (Zamir et al 2017) are suboptimal for use with acquired images whose spatial resolution varies with view angle, such as produced with the partial-dithering strategy. To circumvent this, a modified version of the JR method is employed to reconstruct image estimates from measured intensity data that are dithered at only a subset of view angles. ...
Edge-illumination X-ray phase-contrast tomography (EIXPCT) is a promising imaging technology where partially opaque masks are utilized with laboratory-based X-ray sources to estimate the distribution of the complex-valued refractive index. EIXPCT resolution is mainly determined by the period of a sample mask, but can be significantly improved by a dithering technique. Here, dithering means that multiple images per tomographic view angle are acquired as the object is moved over sub-pixel distances. Drawbacks of dithering include increased data-acquisition times and radiation doses. Motivated by the flexibility in data-acquisition designs enabled by a recently developed joint reconstruction (JR) method, a novel partial-dithering strategy for EIXPCT data-acquisition is proposed. In this strategy, dithering is implemented at only a subset of the tomographic view angles. The strategy can result in spatial resolution comparable to that of the conventional full-dithering strategy, where dithering is performed at every view angle, but the acquisition time is substantially decreased. Here, the effect of dithering parameters on image resolution are explored.
... Compared with conventional computed tomography (CT) techniques, XPCT holds promise to provide better differentiation of soft tissues and generally low Z materials. In recent years, various types of XPCT methods have been developed, including grating-based X-ray phase-contrast tomography (GB-XPCT) [1][2][3], propagation-based X-ray phase-contrast tomography (PB-XPCT) [4][5][6] and edge illumination X-ray phase-contrast tomography (EIXPCT) [7][8][9]. XPCT can be implemented with microfocal sources, but it comes with the expense of greatly increased exposure times [4,10]. For example, a conventional X-ray source can be employed for XPCT imaging in GB-XPCT when a source grating [1] is employed to produce beamlets possessing the necessary spatial coherence. ...
Edge-illumination X-ray phase-contrast tomography (EIXPCT) is an emerging technique that enables practical phase-contrast imaging with laboratory-based X-ray sources. A joint reconstruction method was proposed for reconstructing EIXPCT images, enabling novel flexible data-acquisition designs. However, only limited efforts have been devoted to optimizing data-acquisition designs for use with the joint reconstruction method. In this study, several promising designs are introduced, such as the constant aperture position (CAP) strategy and the alternating aperture position (AAP) strategy covering different angular ranges. In computer-simulation studies, these designs are analyzed and compared. Experimental data are employed to test the designs in real-world applications. All candidate designs are also compared for their implementation complexity. The tradeoff between data-acquisition time and image quality is discussed.
