Collimated X-ray Beam Research Articles

Specification of x-ray mirrors in terms of system performance: new twist to an old plot

In the early 1990s, Church and Takacs pointed out that the specification of surface figure and finish of x-ray mirrors must be based on their performance in the beamline optical system. We demonstrate the limitations of specification, characterization, and performance evaluation based on conventional statistical approaches, including root-mean-square roughness and residual slope variation, evaluated over spatial frequency bandwidths that are system specific, and a more refined description of the surface morphology based on the power spectral density distribution. We show that these limitations are fatal, especially in the case of highly collimated coherent x-ray beams, like beams from x-ray free electron lasers (XFELs). The limitations arise due to the deterministic character of the surface profile data for a definite mirror, while the specific correlation properties of the surface are essential for the performance of the entire x-ray optical system. As a possible way to overcome the problem, we treat a method, suggested by Yashchuk and Yashchuk in 2012, based on an autoregressive moving average modeling of the slope measurements with a limited number of parameters. The effectiveness of the approach is demonstrated with an example specific to the x-ray optical systems under design at the European XFEL.

Measurement of bow tie profiles in CT scanners using a real-time dosimeter.

Several areas of computed tomography (CT) research require knowledge about the intensity profile of the x-ray fan beam that is introduced by a bow tie filter. This information is considered proprietary by CT manufacturers, so noninvasive measurement methods are required. One method using real-time dosimeters has been proposed in the literature. A commercially available dosimeter was used to apply that method, and analysis techniques were developed to extract fan beam profiles from measurements. A real-time ion chamber was placed near the periphery of an empty CT gantry and the dose rate versus time waveform was recorded as the x-ray source rotated about the isocenter. In contrast to previously proposed analysis methods that assumed a pointlike detector, the finite-size ion chamber received varying amounts of coverage by the collimated x-ray beam during rotation, precluding a simple relationship between the source intensity as a function of fan beam angle and measured intensity. A two-parameter model for measurement intensity was developed that included both effective collimation width and source-to-detector distance, which then was iteratively solved to minimize the error between duplicate measurements at corresponding fan beam angles, allowing determination of the fan beam profile from measured dose-rate waveforms. Measurements were performed on five different scanner systems while varying parameters such as collimation, kVp, and bow tie filters. On one system, direct measurements of the bow tie profile were collected for comparison with the real-time dosimeter technique. The data analysis method for a finite-size detector was found to produce a fan beam profile estimate with a relative error between duplicate measurement intensities of <5%. It was robust over a wide range of collimation widths (e.g., 1-40 mm), producing fan beam profiles that agreed with a relative error of 1%-5%. Comparison with a direct measurement technique on one system produced agreement with a relative error of 2%-6%. Fan beam profiles were found to differ for different filter types on a given system and between different vendors. A commercially available real-time dosimeter probe was found to be a convenient and accurate instrument for measuring fan beam profiles. An analysis method was developed that could handle a wide range of collimation widths by explicitly considering the finite width of the ion chamber. Relative errors in the profiles were found to be less than 5%. Measurements of five different clinical scanners demonstrate the variation in bow tie designs, indicating that generic bow tie models will not be adequate for CT system research.

New Virtual Frisch-Grid CdZnTe Detector Design With Sub-Millimeter Spatial Resolution

We evaluated the performance of a position-sensitive virtual Frisch-grid (VFG) CdZnTe detector, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$6~\hbox{mm} \times 6~\hbox{mm} \times 15~\hbox{mm}$</tex></formula> , via sensing strips on its side surfaces. Once the signals were collected from the anode, and from four or eight strips attached to the detector’s sides, we assessed the anode’s energy spectra and derived histograms from the side electrodes to evaluate the feasibility of achieving sub-millimeter spatial resolution in the X-Y plane. Using a highly collimated 30-keV X-ray beam at the National Synchrotron Light Source, and applying corrections to the raw data, we determined the photon-interaction points by conventional Anger logic and via a more sophisticated statistics-based positioning (SBP) algorithm. With the VFG detector’s current configuration, we achieved a resolution below 1 mm, even for low-energy X-rays.

Stored luminescence computed tomography.

Phosphor nanoparticles made of doped semiconductors and pre-excited by x-ray radiation were recently reported for their luminescence emission in the range of 650-770nm upon near-infrared (NIR) light stimulation. These nanophosphors can be functionalized as optical probes for molecular imaging. In this paper, we present stored luminescence computed tomography to reconstruct a nanophosphor distribution in an object. The propagation of x rays in a biological object allows significantly better localization and deeper penetration. Moreover, the nanophosphors, which are pre-excited with collimated x-ray beams or focused x-ray waves, can be successively stimulated for stored luminescence emissions by variable NIR stimulation patterns. The sequentially detected luminescence signals provide more information of a nanophosphor spatial distribution for more accurate image reconstruction and higher image resolution. A realistic numerical study is performed to demonstrate the feasibility and merits of the proposed approach.

A 3D CZT High Resolution Detector for X-and gamma-ray applications.

A high resolution three dimensional (3D) position sensitive CdZnTe-based detector was developed to detect high energy photons (10 keV-1MeV). The design of the 3D CZT detector, developed at DTU Space, is based on the CZT Drift Strip detector principle. The prototype detector contains 12 drift cells, each comprising one collecting anode strip with 3 drift strips, biased such that the electrons are focused and collected by the anode strips. The anode pitch is 1.6mm. The position determination perpendicular to the anodes, the X-direction, is performed using a novel interpolating technique. The position determination along the detector depth direction, Y-direction, is made using the depth sensing technique. The position determination along the anode strips, Z-direction is made with the help of 10 cathode strips orthogonal to the anode strips. REDLEN CZT crystals (20 mm x 20 mm x 5 mm) were used for the proto type detectors. IMEM-CNR fabricated the proto type detectors using a special surface treatment method and electrode attachment process. A novel method was applied to reduce the surface leakage current between the strips. The proto type detector was investigated at the European Synchrotron Radiation Facility, Grenoble which provided a fine 50 x 50 μm2 collimated X-ray beam covering an energy band up to 600 keV. At 400 keV we measured position resolutions of 0.2 mm FWHM in the X- and Y-direction and 0.6 mm FWHM in the Z-direction. The measured energy resolution of the detector was ~5.5 keV FWHM at 400 keV. The electronic noise contribution of the detector setup was 3.7 keV FWHM . The detector provides 3D position with very good spatial resolution as well as high resolution energy information and is therefore a well suited candidate e.g. as a Compton telescope detector, or for any application fields (medicine, security, science) where imaging and spectroscopy of high energy photons in the 10keV-1MeV range are required.

Does the size of a crystal matter in an X-ray crystal structure analysis of a small molecule?

The crystal structures of C7H8FN3, C20H25Br, [Cu(H2O)2(C6H12N4)(C7H3N2O6)2]·2H2O, [SnCl(H2O)(C6H5)3(C10H8N2)]2 and [Pb(NO3)2(C3H9N3S)] refined on numerically absorption-corrected reflections to low R values although the dimensions of the crystals exceeded the diameter of the X-ray beam collimator. The R values for the organic and copper compounds were not significantly different when smaller specimens cut from the large crystals were used. For the tin complex, a large peak persisted in the difference map for all sizes, and for the lead complex, the difference Fourier map was more diffuse the smaller the specimen.

Numerical simulation of x-ray luminescence optical tomography for small-animal imaging

X-ray luminescence optical tomography (XLOT) is an emerging hybrid imaging modality in which x-ray excitable particles (phosphor particles) emit optical photons when stimulated with a collimated x-ray beam. XLOT can potentially combine the high sensitivity of optical imaging with the high spatial resolution of x-ray imaging. For reconstruction of XLOT data, we compared two reconstruction algorithms, conventional filtered backprojection (FBP) and a new algorithm, x-ray luminescence optical tomography with excitation priors (XLOT-EP), in which photon propagation is modeled with the diffusion equation and the x-ray beam positions are used as reconstruction priors. Numerical simulations based on dose calculations were used to validate the proposed XLOT imaging system and the reconstruction algorithms. Simulation results showed nanoparticle concentrations reconstructed with XLOT-EP are much less dependent on scan depth than those obtained with FBP. Measurements at just two orthogonal projections are sufficient for XLOT-EP to reconstruct an XLOT image for simple source distributions. The heterogeneity of x-ray energy deposition is included in the XLOT-EP reconstruction and improves the reconstruction accuracy, suggesting that there is a need to calculate the x-ray energy distribution for experimental XLOT imaging.

Use of TALP with laboratory powder diffraction data from 2D detectors

The viability of the direct-space strategy TALP (Vallcorbaet al., 2012b) to solve crystal structures of molecular compounds from laboratory powder diffraction data is shown. The procedure exploits the accurate metric refined from a ‘Bragg-Brentano’ powder pattern to extract later the intensity data from a second ‘texture-free’ powder pattern with the DAJUST software (Vallcorbaet al., 2012a). The experimental setup for collecting this second pattern consists of a circularly collimated X-ray beam and a 2D detector. The sample is placed between two thin Mylar®foils, which reduces or even eliminates preferred orientation. With the combination of the DAJUST and TALP software a preliminary but rigorous structural study of organic compounds can be carried out at the laboratory level. In addition, the time-consuming filling of capillaries with diameters thinner than 0.3mm is avoided.

Electronic collimation and radiation protection in paediatric digital radiography: revival of the silver lining

In digital radiography we are now able to electronically collimate images after acquisition. This may seem convenient in paediatric imaging, but we have to be aware that electronic collimation has two major downsides. Electronic collimation implicates that the original field size should have been smaller and the child has been exposed to unnecessary radiation. Also, by use of electronic collimation, potentially important information may be lost. The “silver lining”, denoting the X-ray beam collimation, can serve as a useful radiation protection instrument to check for proper field size and detect unnecessary exposure. Furthermore, the silver lining confirms all exposed anatomy is shown in the final image, and thus may also serve as a quality assurance instrument as the patient has the right to all acquired information. Teaching Points • The ability to electronically collimate an image after acquisition may serve to enhance contrast in the region of interest.• The ability to electronically collimate an image after acquisition carries the risk of overexposure.• The ability to electronically collimate an image after acquisition carries the risk of losing important information.• The silver lining can serve as a quality control instrument for proper collimation.• The patient has the right to all information obtained during an X-ray examination.

X-ray luminescence optical tomography imaging: experimental studies

We present a hybrid imaging modality, x-ray luminescence optical tomography (XLOT), in which collimated x-ray beams are used to excite phosphor-based contrast agents. Images are reconstructed from the optical signals, using the known x-ray beam location and spatial extent as priors. We demonstrate XLOT using phantom experiments with deep targets and show that the reconstructed signal varies by <12% when the depth changes from 4.2 to 7.7mm. For simple source distributions, we find as few as two orthogonal projection measurements are sufficient for XLOT reconstruction.

Development of an on-axis-visualization stage to observe and align sample with an x-ray beam

An on-axis-visualization stage for accurate sample alignment respect to X-ray beam has been designed and implemented at the diffraction and absorption/fluorescence stations of the BM25-SpLine synchrotron beamline at the ESRF. It is mostly intended for studies involving heterogeneous samples where the analysis is restricted to a particular area of the sample. The OAV system provides a parallax-free image of the sample. This is accomplished by a front-surface mirror at an angle of 45° degrees to reflect the visible sample image 90° up to a zoom optics and digital colour CCD camera. A pinhole (PH) on the mirror in combination with a second PH 100 mm backward provides an on-axis collimated X-ray beam at image centre. The collimator is aligned to the beam axis by two angular and two translational high-precision motorized motions. The OAV stage is synchronized with the sample positioning stage, by a computer software so that the desired sample region is aligned on the X-ray beam by selecting it on the image produced by the video camera. In this work, a complete description of the on-axis-visualization system will be presented including the experimental determination of the alignment accuracy.

A high pressure XRD setup at ADXRD beamline (BL-12) on Indus-2

A high pressure XRD measurement setup in the angle dispersive geometry has been setup in the Angle Dispersive X-ray diffraction beamline (BL-12) in Indus-2 synchrotron facility. The X-Ray beam is collimated inside the diamond anvil cell (DAC) using a pair of cross-slit collimators and 100 micron orifice in a 400 micron thick Ta sheet. With the use of an adaptive optics to ensure a converging beam at the sample position, the need of an x-ray beam collimator is eliminated making the alignment of the DAC quite easy. The alignment of the DAC with respect to the incident x-ray beam is made by placing it on a computer controlled sample mounting and alignment stage developed specifically for this setup. Interactive software has been developed to make the alignment of the X-ray through the DAC very easy and accurate. NIST standard LaB6 powder was used for test runs, and a few fine pieces of gold served as pressure calibrator. The data was recorded on a MAR345 Image plate detector.

Nationwise Survey of the X-ray Beam Collimator Utilization in General Diagnostic Radiograph

†‡ § Due to the introduction of CR and DR, it has been neglected the use of the X-ray beam collimator and field size. This study examines nationwide survey of the proper use of collimator and field size by area in a specific field of plain radiography and the current status. Authors emphasized the need for the field size criteria, and propose a standard reference field size in each specific radiologic examination. Total 333 medical institutions (included in Seoul, Gyeonggi-do, Jeolla, Chungcheong, Gangwon-do, Busan area), were investigated in relation to the status of the X-ray beam collimation field size, type specific inspection areas, medical facilities, and image analyses by type to figure out whether they use the adjustment of image field to the specific examination. To assess the awareness and the impact of radiation exposure to th e collimation adjustable, 168 radiographers who was working in 10 general hospitals, 10 hospitals, and 10 clini cs, were surveyed how they haver adjusted the actual field size. We examine that 61.3% of medical institution s used the “Proper collimation” and only 49.9% of them employed proper one in lumbar spine densely crowded by major organs. 69% among general hospitals, and 65% among hospitals using DR system were using proper colli mation. Radiographers recognized that proper adjustment of collimation could reduce the harmful radiation do se on patients. In the survey, 97.6% of respondents were aware of this fact, but only 83.3% of respondents did the adjustment of the size of the collimation field. The using of proper collimation field was low in the nationwide survey, so the effort to reduce the radiation dose on the patients is urgently needed. A unified standard for the field accompanied by thorough education should be needed.

Multi-Layer Organic Squaraine-Based Photodiode for Indirect X-Ray Detection

The paper presents an organic-based photodiode coupled to a CsI(Tl) scintillator to realize an X-ray detector. A suitable blend of an indolic squaraine derivative and of fullerene derivative has been used for the photodiode, thus allowing external quantum efficiency in excess of 10% at a wavelength of 570 nm, well matching the scintillator output spectrum. Thanks to the additional deposition of a 15 nm thin layer of a suitable low electron affinity polymer, carriers injection from the metal into the organic semiconductor has been suppressed, and dark current density as low as has been obtained, which is comparable to standard Si-based photodiodes. By using a collimated X-ray beam impinging onto the scintillator mounted over the photodiode we have been able to measure current variations in the order of 150 pA on a dark current floor of less than 50 pA when operating the X-ray tube in switching mode, thus proving the feasibility of indirect X-ray detection by means of organic semiconductors.

Strict X-ray beam collimation for facial bones examination can increase lens exposure.

It is well accepted that collimation is a cost-effective dose-reducing tool for X-ray examinations. This phantom-based study investigated the impact of X-ray beam collimation on radiation dose to the lenses of the eyes and thyroid along with the effect on image quality in facial bone radiography. A three-view series (occipitomental, occipitomental 30 and lateral) was investigated, and radiation doses to the lenses and thyroid were measured using an Unfors dosemeter. Images were assessed by six experienced observers using a visual grading analysis and a total of 5400 observations were made. Strict collimation significantly (p<0.0001) reduced the radiation dose to the lenses of the eyes and thyroid when using a fixed projection-specific exposure. With a variable exposure technique (fixed exit dose, to simulate the behaviour of an automatic exposure control), while strict collimation was again shown to reduce thyroid dose, higher lens doses were demonstrated when compared with larger fields of exposure. Image quality was found to significantly improve using strict collimation, with observer preference being demonstrated using visual grading characteristic curves. The complexities of optimising radiographic techniques have been shown and the data presented emphasise the importance of examining dose-reducing strategies in a comprehensive way.

&lt;i&gt;In Situ&lt;/i&gt; Gas Supply System on the Powder Diffraction Beamline I11 at Diamond Light Source

Beamline I11 at Diamond began accepting users for high resolution powder diffraction experiments in Oct 2008. We present the design, key specifications, performance and the hardware of this new beamline which receives an intense and highly collimated x-ray beam generated by an in-vacuum undulator. With the simple optics (a double-crystal monochromator, harmonic rejection mirrors and slits), a high purity beam of low energy-bandpass X-rays optimised at 15 keV is delivered at the sample. The heavy duty diffraction instrument is designed to have the flexibility to house a variety of sample environments and holds two detection systems to collect high quality diffraction data, i.e. multi-analysing crystals (MAC) for high angular resolution experiments and a fast position sensitive detector (PSD) for time-resolved studies. A recent addition to the beamline capabilities is the installation of a specifically designed gas control system. This allows the in-situ dosing of a powder sample with gases such as hydrogen and carbon dioxide, at low (~10 mbar) and high pressures (&lt;100 bar). In addition a low pressure capillary sample cell is described which is now available to users of the beamline.

Analysis of X-ray phase contrast imaging in atomizing sprays

Recent studies of spray-related flow fields using synchrotron-based X-ray phase contrast imaging have produced results that are sometimes straightforward to interpret in terms of the fluid structure, but in other cases the images do not reflect generally accepted physics of fluid motion. It has been unclear why some images have the appearance of a normal fluid stream while others depart significantly from expectation. The detailed numerical modeling presented here is meant to explain the images and resolve common questions about the technique. The simulations show that collimated X-ray beams will always contain signatures from every possible encounter, from the input plane to the exit plane, and these signatures generate overlapping phase contrast patterns that can prove at times impossible to interpret. Clouds of moderate- to large-size drops produce a complex, mottled X-ray phase contrast image indicating the presence of the cloud; but it is an image that cannot be interpreted further. Small drops generate something akin to one gray pixel image each, and their size is close to the resolution limit of the instrument, so the diffraction pattern is broadened by the instrument response into something more like a small diffuse blob. Dense clouds of small drops produce a composite image that is a fairly uniform gray mass indicating the presence of a drop cloud that cannot be interpreted further. Moreover, it is not possible to image intact liquid structures behind clouds of drops. Whenever a significant number of drops are present, therefore, X-ray phase contrast images are dominated by unavoidable artifacts of the technique. Sprays, by definition, consist of droplet clouds and this means that internal features in the spray formation region cannot be investigated using X-ray phase contrast imaging.

SU-E-I-156: CT Dose in Pediatric PET/CT Examinations

Purpose: To optimize CT protocols for pediatric whole-body PET/CT examination and to evaluate radiation dose. Methods: We developed pediatric whole-body CT acquisition protocols used for attenuation correction and localization of the PET data. Patients were categorized in 6 groups according to their weight and age, similar to the Broselow—Luten color-coded scale. X-ray tube current modulation was employed in all protocols with maximum mAs ranging from 25 to 55. The acquisition parameters were as follows: 100 kVp; 16×1.25 mm X-ray beam collimation; 27.1 Noise Index; 1.35:1 pitch; 0.5 s rotation time; and 3.75 mm reconstructed slice thickness. For the senior group of 12 – 17 years of age (50 – 70 kg) we used 120 kVp and 50 max mAs. All data were acquired on a GE Discovery STE 16 PET/CT scanner, and patients were injected with 5.55 MBq (0.15 mCi) of 18F-FDG per kg of weight. We surveyed pediatric studies performed in our institution during the period of 2009 – 2010. There were 27 patients from 18 months to 17 years of age, and 12 of them had had multiple exams (up to 6). Overall, 54 pediatric studies were performed over the two-year period. Effective CT dose was calculated using the dose length product (DLP) values from the patientsˈ dose reports and conversion factors (normalized effective dose per DLP), dependant on the patient age. Results: Effective CT doses were in the range from 0.91 mSv to 3.6 mSv for all patient categories. Comparison with published data based on 11 patient weight categories demonstrated lower dose in each patient group achieved with the acquisition protocols developed in our institution. Conclusions: Pediatric CT protocols for 6 patient weight/age-based categories were developed for the whole-body PET/CT. Patientsˈ dose survey demonstrated lower effective CT dose than reported in the literature for each weight category.

Limited-angle x-ray luminescence tomography: methodology and feasibility study

X-ray luminescence tomography (XLT) has recently been proposed as a new imaging modality for biological imaging applications. This modality utilizes phosphor nanoparticles which luminesce near-infrared light when excited by x-ray photons. The advantages of this modality are that it uniquely combines the high sensitivity of radioluminescent nanoparticles and the high spatial localization of collimated x-ray beams. Currently, XLT has been demonstrated using x-ray spatial encoding to resolve the imaging volume. However, there are applications where the x-ray excitation may be limited by geometry, where increased temporal resolution is desired, or where a lower dose is mandatory. This paper extends the utility of XLT to meet these requirements by incorporating a photon propagation model into the reconstruction algorithm in an x-ray limited-angle (LA) geometry. This enables such applications as image-guided surgery, where the ability to resolve lesions at depths of several centimeters can be the key to successful resection. The hybrid x-ray/diffuse optical model is first formulated and then demonstrated in a breast-sized phantom, simulating a breast lumpectomy geometry. Both numerical and experimental phantoms are tested, with lesion-simulating objects of various sizes and depths. Results show localization accuracy with median error of 2.2 mm, or 4% of object depth, for small 2–14 mm diameter lesions positioned from 1 to 4.5 cm in depth. This compares favorably with fluorescence optical imaging, which is not able to resolve such small objects at this depth. The recovered lesion size has lower size bias in the x-ray excitation direction than the optical direction, which is expected due to the increased optical scatter. However, the technique is shown to be quite invariant in recovered size with respect to depth, as the standard deviation is less than 2.5 mm. Sensitivity is a function of dose; radiological doses are found to provide sufficient recovery for µg ml−1 concentrations, while therapy dosages provide recovery for ng ml−1 concentrations. Experimental phantom results agree closely with the numerical results, with positional errors recovered within 8.6% of the effective depth for a 5 mm object, and within 5.2% of the depth for a 10 mm object. Object-size median error is within 2.3% and 2% for the 5 and 10 mm objects, respectively. For shallow-to-medium depth applications where optical and radio-emission imaging modalities are not ideal, such as in intra-operative procedures, LAXLT may be a useful tool to detect molecular signatures of disease.

Architecture of a Full-length Retroviral Integrase Monomer and Dimer, Revealed by Small Angle X-ray Scattering and Chemical Cross-linking

We determined the size and shape of full-length avian sarcoma virus (ASV) integrase (IN) monomers and dimers in solution using small angle x-ray scattering. The low resolution data obtained establish constraints for the relative arrangements of the three component domains in both forms. Domain organization within the small angle x-ray envelopes was determined by combining available atomic resolution data for individual domains with results from cross-linking coupled with mass spectrometry. The full-length dimer architecture so revealed is unequivocally different from that proposed from x-ray crystallographic analyses of two-domain fragments, in which interactions between the catalytic core domains play a prominent role. Core-core interactions are detected only in cross-linked IN tetramers and are required for concerted integration. The solution dimer is stabilized by C-terminal domain (CTD-CTD) interactions and by interactions of the N-terminal domain in one subunit with the core and CTD in the second subunit. These results suggest a pathway for formation of functional IN-DNA complexes that has not previously been considered and possible strategies for preventing such assembly.