Computed Tomography Apparatus Research Articles

2DeteCT - A large 2D expandable, trainable, experimental Computed Tomography dataset for machine learning

Recent research in computational imaging largely focuses on developing machine learning (ML) techniques for image reconstruction, which requires large-scale training datasets consisting of measurement data and ground-truth images. However, suitable experimental datasets for X-ray Computed Tomography (CT) are scarce, and methods are often developed and evaluated only on simulated data. We fill this gap by providing the community with a versatile, open 2D fan-beam CT dataset suitable for developing ML techniques for a range of image reconstruction tasks. To acquire it, we designed a sophisticated, semi-automatic scan procedure that utilizes a highly-flexible laboratory X-ray CT setup. A diverse mix of samples with high natural variability in shape and density was scanned slice-by-slice (5,000 slices in total) with high angular and spatial resolution and three different beam characteristics: A high-fidelity, a low-dose and a beam-hardening-inflicted mode. In addition, 750 out-of-distribution slices were scanned with sample and beam variations to accommodate robustness and segmentation tasks. We provide raw projection data, reference reconstructions and segmentations based on an open-source data processing pipeline.

A freely distributable professional computed tomography system using NICOS

Based on the control system of the ANTARES neutron imaging system at FRM II, we have designed a portable, but professional neutron computed tomography system using the same TANGO device servers and the instrument control system NICOS. We have created a minimalistic setup to control a computed tomography setup using a single control computer that directly connects to a camera detector and interfaces a Raspberry Pi computer with motor control board via a local network. The setup has the full capability of a large instrument controller and can control arbitrary hardware (like professional motor controllers) for which hundreds of free drivers are available. Full schematics for the controller as well as print files for 3D printers for the detector housing and disk or virtual machine images are available for free to allow for the quick implementation of a low-cost, but professional neutron CT system even at very low power research reactors.

Spherical acquisition trajectories for x-ray computed tomography with a robotic sample holder

This work presents methods for the seamless execution of arbitrary spherical trajectories with a seven-degree-of-freedom robotic arm as a sample holder. The sample holder is integrated into an existing x-ray computed tomography setup. We optimized the path planning and robot control algorithms for the seamless execution of spherical trajectories. A precision-manufactured sample holder part is attached to the robotic arm for the calibration procedure. Different designs of this part are tested and compared to each other for optimal coverage of trajectories and reconstruction image quality. We present experimental results with the robotic sample holder where a sample measurement on a spherical trajectory achieves improved reconstruction quality compared to a conventional circular trajectory. Our results demonstrate the superiority of the discussed system as it outperforms single-axis systems by reaching nearly 82% of all possible rotations. The proposed system is a step towards higher image reconstruction quality in flexible x-ray CT systems. It will enable reduced scan times and radiation dose exposure with task-specific trajectories in the future, as it can capture information from various sample angles.

Intraoperative computed tomography during fenestrated and branched endovascular aortic repair: a feasibility study.

Endovascular aortic repair with fenestrated or branched endografts is technically challenging, and proper intraoperative assessment of all stent graft components with only angiography and fluoroscopy can be difficult. Intraoperative computed tomography (CT) imaging can be a valuable aid for the operators in the evaluation of stent grafting results prior to completion of surgery. To examine the feasibility of performing intraoperative CT imaging during fenestrated and branched endovascular aortic repair (f-bEVAR) under sterile conditions and with patients under general anesthesia. Intraoperative CT imaging was performed in 10 patients undergoing elective aortic repair with fenestrated or branched endografts. Adverse events, time consumption for CT set-up and image acquisition, and additional radiation dose to the patient were recorded. CT image quality was graded. Immediate corrective maneuvers performed based on the CT findings was registered. There were no adverse events related to intraoperative CT imaging. The median additional operating time by including intraoperative CT was 16 min (interquartile range [IQR] = 12-19), comprising 7% of the median total operating time. The median estimated additional radiation dose to the patient was 4.8 mSv (IQR = 3.8-4.9). All intraoperative CT examinations were considered to be of sufficient quality for stent graft evaluation. No immediate corrective procedures were performed on the basis of CT findings in this study cohort. CT imaging intraoperatively during f-bEVAR is feasible with an acceptable increase in operating time and radiation dose.

Calibration of 3D scan trajectories for an industrial computed tomography setup with 6-DOF object manipulator system using a single sphere

In industrial x-ray computed tomography (CT), the application of more complex scan paths in comparison to the typical circular trajectory ( rotation of the measurement object) can extend the potential of CT. One way to enable such 3D scan trajectories is to use a 6-degrees-of-freedom (DOF) object manipulator system. In our case, a hexapod is mounted on top of the rotary table of a commercial CT scanner. This allows for adaptive tilting of the measurement object during the scan. For high accuracy, the geometry calibration of such setups is typically done using the x-ray projections of a calibrated multi-sphere object. Contrary to this, here, we demonstrate a procedure that is based on only a single sphere and can therefore experimentally be implemented with low effort. Using the intrinsic geometry parameters of the CT device as prior information, the hexapod coordinate system with respect to the CT machine coordinate system is determined by means of a one-step optimization approach. The resulting parameters are used to calculate projection matrices that enable the volume reconstruction for 3D scan trajectories. The method is validated using simulated x-ray images and experimental investigations including dimensional measurements. For the used setup, geometric measurement results for 3D scan trajectories that are calibrated with the presented method show in sum increased errors compared to the circular scans. A limited pose accuracy of the manipulator system is discussed as a potential cause. The results nevertheless indicate that the presented method is generally feasible for dimensional CT measurements provided that the pose accuracy is sufficient. The calibration procedure can therefore be a low-cost and easier to implement alternative compared to trajectory calibration methods based on multi-sphere objects, but with a tendency towards lower measurement accuracy. The methodology can in principle be transferred to different setups with 6-DOF manipulator systems, e.g. C-arm CT devices with a robot arm.

X-ray computed tomography with seven degree of freedom robotic sample holder

We present an x-ray Computed Tomography setup that integrates a seven degrees of freedom robotic arm as a sample holder within an existing laboratory x-ray computed tomography setup. We aim to provide a flexible sample holder that is able to execute non-standard and task-specific trajectories for complex samples. The robotic arm is integrated with a unified software package that allows for path planning, collision detection, geometric calibration and reconstruction of the sample. The calibration is necessary to identify the accurate pose of the sample which deviates from the expected pose due to inaccurate placement of the robotic arm. With our software the user is able to command the robotic arm to execute arbitrary trajectories for a given sample in a safe manner and output its reconstruction to the user. We present experimental results with a circular trajectory where the robotic sample holder achieves identical visual quality compared to a conventional sample holder.

Analytical setup margin for spinal stereotactic body radiotherapy based on measured errors

BackgroundNo consensus currently exists about the correct margin size to use for spinal SBRT. Margins have been proposed to account for various errors individually, but not with all errors combined to result in a single margin value. The purpose of this work was to determine a setup margin for five-fraction spinal SBRT based on known errors during radiotherapy to achieve at least 90% coverage of the clinical target volume with the prescription dose for at least 90% of patients and not exceed a 30 Gy point dose or 23 Gy to 10% of the spinal cord subvolume.MethodsThe random and systematic error components of intrafraction motion, residual setup error, and end-to-end system accuracy were measured. The patient’s surface displacement was measured to quantify intrafraction motion, the residual setup error was quantified by re-registering accepted daily cone beam computed tomography setup images, and the displacement between measured and planned dose profiles in a phantom quantified the end-to-end system accuracy. These errors and parameters were used to identify the minimum acceptable margin size. The margin recommendation was validated by assessing dose delivery across 140 simulated patient plans suffering from various random shifts representative of the measured errors.ResultsThe errors were quantified in three dimensions and the analytical margin generated was 2.4 mm. With this margin applied in the superior/inferior direction only, at least 90% of the CTV was covered with the prescription dose for 96% of the 140 patients simulated with minimal negative effect on the spinal cord dose levels.ConclusionsThe findings of this work support that a 2.4 mm margin applied in the superior/inferior direction can achieve at least 90% coverage of the CTV for at least 90% of dual-arc volumetric modulated arc therapy spinal SBRT patients in the presence of errors when immobilized with vacuum bags.

Feasibility Studies of X-Ray Computed Tomography for Forensic Examination of Single Fibers.

Non-destructive observations of cross-sectional shapes of acrylic single fibers using X-ray computed tomography (CT) were performed. A commercial X-ray CT apparatus (Rigaku nano3DX) was employed because of its micrometer-scale spatial resolution and remarkable image contrast for soft matter. We assessed two types of sample support, a paraffin strip and a nylon string, for single fiber samples in terms of easy handling and sample recovery. Fixed individual single fibers were loaded into a narrow polyimide tube in both cases, and the tube ensured that the sample remained in the field of view during the CT measurements. In both cases, the cross-sectional shapes of individual single fibers could be distinguished, with a circular shape for one sample and a triangular shape for the other. However, the support using a nylon string was found to be more suitable for further analysis. The cross-sectional profile of the obtained tomographic image showed a clear difference between polyimide and nylon. The intensity ratio or the image contrast corresponded to that of the local densities. It was also found that the effect of the artifact appeared at around the boundaries of the objects, but the local density could still be utilized for examining individual single fibers.

Optimizing iterative reconstruction for quantification of calcium hydroxyapatite with photon counting flat-detector computed tomography: a cardiac phantom study.

.Purpose: Coronary artery calcium (CAC) scoring with computed tomography (CT) has been proposed as a screening tool for coronary artery disease, but concerns remain regarding the radiation dose of CT CAC scoring. Photon counting detectors and iterative reconstruction (IR) are promising approaches for patient dose reduction, yet the preservation of CAC scores with IR has been questioned. The purpose of this study was to investigate the applicability of IR for quantification of CAC using a photon counting flat-detector.Approach: We imaged a cardiac rod phantom with calcium hydroxyapatite (CaHA) inserts with different noise levels using an experimental photon counting flat-detector CT setup to simulate the clinical CAC scoring protocol. We applied filtered back projection (FBP) and two IR algorithms with different regularization strengths. We compared the air kerma values, image quality parameters [noise magnitude, noise power spectrum, modulation transfer function (MTF), and contrast-to-noise ratio], and CaHA quantification accuracy between FBP and IR.Results: IR regularization strength influenced CAC scores significantly (). The CAC volumes and scores between FBP and IRs were the most similar when the IR regularization strength was chosen to match the MTF of the FBP reconstruction.Conclusion: When the regularization strength is selected to produce comparable spatial resolution with FBP, IR can yield comparable CAC scores and volumes with FBP. Nonetheless, at the lowest radiation dose setting, FBP produced more accurate CAC volumes and scores compared to IR, and no improved CAC scoring accuracy at low dose was demonstrated with the utilized IR methods.

X-ray tomographic data of planktonic foraminifera species Globigerina bulloides from the Eastern Tropical Atlantic across Termination II.

Increased planktonic foraminifera shell weights were recorded during the course of Termination II at a tropical site off the shore of the Mauritanian coast. In order to investigate these increased shell mass values, a series of physicochemical analyses were performed, including X-ray computed tomography (CT). The data are given here. Furthermore, the relevant CT setup, scanning, reconstruction, and visualization methods are explained and the acquired datasets are given, together with 3D volumes and models of the scanned specimens.

A technique for in situ X-ray computed tomography of deformation-induced cavitation in thermoplastics

Deformation-induced cavitation influences the mechanical response of polymeric materials, but acquiring in situ measurements of the spatial evolution of cavities has typically necessitated the use of synchrotron radiation sources. The objective of this study is to develop and demonstrate a method allowing for in situ measurements of deformation-induced cavitation in axisymmetric polymer specimens, using a home-laboratory X-ray computed tomography setup. The method is demonstrated by assessing deformation-induced cavitation of mineral-filled PVC in a repeated loading-unloading experiment. A temporal resolution of about 3 s is obtained by exploiting the axisymmetry of notched round tensile specimens. The evolution of relative density was captured throughout the experiment, revealing an interplay between void nucleation and void growth. Combined with surface deformation measurements obtained by digital image correlation, the present technique yields data suitable for calibration and validation of material models.

In situ observation of austenite coarsening induced by massive-like transformation during solidification in Fe–C alloys

A massive-like transformation, in which δ-ferrite massively transforms to γ-austenite in the solid state, was examined by time-resolved X-ray imaging and X-ray diffractometry on a four-dimensional–computed tomography setup. In the unidirectional solidification of a hyperperitectic steel (0.3 mass% C) at 50 μm/s, δ dendrites, fine γ grains that are produced through the massive-like transformation, and coarse γ grains grow together in the steady state. The massive-like transformation occurred commonly in Fe-based alloys with a peritectic reaction in equilibrium. Time-resolved X-ray diffraction measurements for a peritectic steel (0.18 mass% C) showed that the massive-like transformation induced strains in the γ grains. The fine γ grains coarsened and/or vanished and new γ grains formed. The induced strains were released during coarsening. The results obtained by the observations contribute to building of a physical model for γ grain coarsening.

Reactivity of Gypsum-Based Materials Subjected to Thermal Load: Investigation of Reaction Mechanisms.

The thermal stability of gypsum-based materials, and in this context, especially their long-term behavior, is the background of our current research activities. A comprehensive investigation program was compiled in which detailed examinations of various model materials exposed to thermal loads were carried out. The understanding of the partly not entirely consistent state of knowledge shall be sharpened especially by in situ observations of the thermally induced conversion reaction of gypsum into hemihydrate. The temporal course of the reaction was investigated non-destructively by in situ investigations in a high-resolution X-ray computed tomography setup, and the experiment was accompanied by detailed characterizations of the microstructure and composition. In this contribution, selected results of experiments with a high-purity natural gypsum rock as the model substance are presented. Studying the influence of temperature on the reaction showed that, even under supposedly dry conditions, the reaction could take place at much lower temperatures than usually reported in the literature. It was demonstrated that the transformation of gypsum into hemihydrate could take place at a temperature of already 50 °C. The results indicated that even under “classical” heating conditions in a conventional oven, the dissolution and crystallization processes in water films on the mineral surfaces could be suggested to be a driving force for the reaction. A corresponding reaction model, which took these aspects into account, was proposed in this work.

Virtual Experimental Analyzes of the Normal and Arthrotic Hip

The hip joint is spheroidal type which allows three movement axes, with a special importance in statics and locomotion. The study of the hip joint by computerized tomography of a male, 52-year-old male patient at the Craiova County Emergency Clinical Hospital was started using Siemens equipment comprised of a magnetic resonance device and a computed tomography apparatus. Were analyzed: hip joint with the two main components of the femur and pelvic bones. To obtain the virtual components of the hip joint, 143 tomographic images from different planes were analyzed. CT images were used to define the normal hip joint. Also, the arthrotic hip virtual model was generated. These two virtual models were subjected to normal walking load and were simulated by the finite element method. The results were analyzed and compared, and important conclusions were finally drawn.

Investigation of the independence of the best assembly orientations with respect to X-ray source parameters in industrial computed tomography

Industrial computed tomography (CT) is a proper tool for extracting both internal and external geometry in one measuring procedure without destroying or rebuilding an assembly. The diversity of assemblies and unique measurement requirements demand an expert user to be able to determine appropriate CT setup parameters. Recent publications have concentrated on the automatic choice of the CT setup parameters or on the determination of features to qualify the chosen setup parameters. Setup parameters consist of X-ray source parameters (i.e., voltage, current, and exposure time), a number of projections, a source-to-object distance (SOD), and an assembly orientation. For multi-material assemblies, it is advantageous to combine two different energies from one or two X-ray sources. Benefits of this combination are a reduction of artifacts, caused by a high absorbing material, and a increased resolution of the CT acquisition (i.e., the combination of high-voltage and low voltage-micro targets). On the basis of previous works, the assembly orientation depends on other CT parameters and requires a correction between measurements with different energies. However, to avoid additional uncertainties due to the fusion of CT volumes, the assembly orientation in the CT system should remain constant for both of the measurements. This study considers the independence of the best assembly orientation tendency and X-ray source parameters. To test the concept, the authors produced CT acquisitions of a multi-material assembly (a polyoxymethylene (POM) cube with two aluminum cylinders) in four different assembly orientations. The choice of assembly orientations was based on the sorted list of minimal required energy. The two sets of X-ray setup parameters that were chosen for the experiment were maximally distant from each other. The concept was validated by statistical analysis of the standard deviations on 48 features of the assembly. The results demonstrated that the group with the best assembly orientations is independent of the X-ray source parameter sets.

Homemade computed tomography setup with FDK reconstruction software

X-ray source, detector and rotation stage as the sample holder were used to built the hardware part of the homemade CBCT scanner. The full scale numerical simulation of the CBCT experiment was modified to complete the scanner. This C/C++ software package is capable to process an arbitrary CT experimental or synthesized data for 3D reconstruction using the FDK method. The high degree of the package’s flexibility allows different CBCT recording and reconstruction geometries with different source and detector positions and their spatial trajectory. The classical computed tomography arrangement, when the gantry, rotating around the sample, is loaded with the opposed sources and detectors, was replaced by the rotating sample and fixed source and detector. Mismatches between these two schemes in reconstruction procedure such as misplacement of the rotation axis from the expected location and other misalignments are compensated by introducing the corresponding variables in the reconstruction software.

Tracking of the Growth Interface during PVT-Growth of SiC Boules Using a X-Ray Computed Tomography Setup

A crystal comprising various polytype switches was analyzed in detail. A very flat temperature profile together with an on axis seed are used to increase the probability for the nucleation of foreign polytypes during growth. Formation of foreign polytype occurred from thin lamella propagating from the edge of the main facet to the crystal rim as well as from 2D nucleation. The evolution of the crystal surface during the growth time is visualized using in-situ X-Ray computed tomography. Two concurrent growth centers are identified in the beginning of the growth process. Nucleation and lateral growth of foreign polytypes in the main facet area can be traced during the growth process.

Investigating the influence of workpiece placement on the uncertainty of measurements in industrial computed tomography

Industrial X-ray computed tomography (CT) is a powerful technique for producing a three-dimensional model of an object and for performing dimensional measurements of an object’s inner and outer features. The diversity of the measuring objects causes a variety of CT setup parameters. The chosen CT setup parameters influence the uncertainty of dimensional measurements. A CT user determines the workpiece orientation and the distance between the workpiece and the X-ray source before a CT scan is commenced, and all other CT setup parameters are based on the workpiece placement inside the CT system. Hence, the workpiece placement is the trend-setting parameter of a CT scan. This paper presents a method for optimising a workpiece placement for dimensional measurements of multi-material workpieces. The method works with the stereolithography (STL) model of the workpiece and analytically tests the whole placement range to find the placement that minimises the attenuation power of a workpiece. The method is validated by analysing the standard deviation of CT measurements on a multi-material workpiece. An analysis of variance on the uncertainty contributions demonstrated that the predicted workpiece placement was optimal.

Development of an attenuation correction method for direct x-ray fluorescence (XRF) imaging utilizing gold L-shell XRF photons.

This work proposes a semiempirical correction method for attenuation of x-ray fluorescence (XRF) photons and/or an excitation beam during direct XRF imaging (i.e., mapping) of gold nanoparticle (GNP) distribution utilizing gold L-shell XRF photons. The current method was first devised by finding the two following relationships: (a) ratio of gold XRF peak intensity (Lα at ~9.7keV and Lβ at ~11.4keV) vs pathlength of XRF photons; (b) XRF photon counts produced (Nxrf ) vs scattered photon counts produced (Nscat ). Monte Carlo simulations were performed using the Geant4 tool kit to characterize the aforementioned relationships for different tissue-like media. The applicability of the method was tested experimentally by acquiring 2D L-shell XRF images of custom-made phantoms using an experimental benchtop x-ray fluorescence computed tomography setup. The results show that the ratio of gold L-shell XRF peak intensities allowed an estimation of the pathlength of XRF photons, thus can be utilized to correct for attenuation of XRF photons after emission. The results also demonstrate that Nscat , through a proportionality where the exponent T depends on the energy of scattered photons, could be used to correct for attenuation of an excitation beam prior to producing XRF photons. The corrected XRF signal was found independent of the densities of tissue-like media present along the passage of an excitation beam or emitted XRF photons. The current results suggest that the developed attenuation correction method plays an essential role for the detection of GNPs on the order of parts-per-million, and also for the determination of GNP concentration/location within the imaging object made of tissue-like media, without any prior knowledge of the imaging object shape, under the conditions deemed relevant to biomedicalapplications of gold L-shell XRF-based imaging.

Determination of the optimal imaging parameters in industrial computed tomography for dimensional measurements on monomaterial workpieces

Industrial computed tomography (CT) plays a key role in 3D coordinate metrology as an alternative to conventional coordinate measuring machines. CT measurement uncertainty depends on the setup parameters with which CT scans are performed. Currently, there is no established model that can describe the relationship between CT setup parameters and measurement uncertainty, and thus determine the optimal settings for a given measurement task. In practice, CT users choose setup parameters intuitively causing high variability in the measurement results. In this study, we enhance and validate an analytical method for optimizing imaging parameters. The proposed method is based on the assumption that minimizing the contribution of imaging parameters to measurement uncertainty corresponds to (1) maximizing image contrast and signal, (2) minimizing geometric blurring, and (3) minimizing image noise and CT artifacts. It also requires information about the workpiece nominal geometry and material composition. The proposed method calculates the optimal photon energy for precise surface determination, given the workpiece position and orientation. Tube voltage and prefilter are determined so that the resulting x-ray spectrum has an effective energy equal to the optimal energy and beam hardening artifacts are minimized. Tube current is chosen to maximize image signal, while avoiding blurring and excessive generated tube power. Exposure time is chosen as the shortest time that fully exploits the detector dynamics. The proposed method was validated by analyzing the standard deviations of CT measurements on a test phantom. An analysis of variance on the uncertainty components showed that the predicted parameters were globally optimal.