Cone-beam System Research Articles

AIRPORT: A Data Consistency Constrained Deep Temporal Extrapolation Method To Improve Temporal Resolution In Contrast Enhanced CT Imaging.

Typical tomographic image reconstruction methods require that the imaged object is static and stationary during the time window to acquire a minimally complete data set. The violation of this requirement leads to temporal-averaging errors in the reconstructed images. For a fixed gantry rotation speed, to reduce the errors, it is desired to reconstruct images using data acquired over a narrower angular range, i.e., with a higher temporal resolution. However, image reconstruction with a narrower angular range violates the data sufficiency condition, resulting in severe data-insufficiency-induced errors. The purpose of this work is to decouple the trade-off between these two types of errors in contrast-enhanced computed tomography (CT) imaging. We demonstrated that using the developed data consistency constrained deep temporal extrapolation method (AIRPORT), the entire time-varying imaged object can be accurately reconstructed with 40 frames-per-second temporal resolution, the time window needed to acquire a single projection view data using a typical C-arm cone-beam CT system. AIRPORT is applicable to general non-sparse imaging tasks using a single short-scan data acquisition.

Direct voxel classification from x-ray projections for 3D pore detection applied to laser sintered parts

X-ray computed tomography (XCT) is a validated and frequently used tool to verify part geometry and to perform a non-destructive inspection of additive manufacturing parts. However, the acquisition of a large number of x-ray projections generates long inspection times. This conflicts with a high throughput of the production process and hinders the integration of XCT as an in-line quality control procedure for low-end parts. In this paper, we propose a method to obtain three-dimensional (3D) information of the internal pores from a limited view or limited angle scan. The method combines a forward projection model of a cone-beam x-ray system and a deep learning neural network to directly classify each individual voxel, based on the x-ray projections in order to avoid the reconstruction and segmentation step. Accompanying reconstruction artifacts for limited view and limited angle XCT scans are thereby reduced, while preserving 3D information of the pores, defects or inclusions inside the material. The method is validated on real x-ray projections of polymer laser sintered industrial parts and shows a significant reduction in the required x-ray projections, hence acquisition time.

Characterization of a polychromatic microfocus X-ray fluorescence imaging setup with metallic contrast agents in a microphysiological tumor model

Introduction: Accurate diagnosis and personalized treatments involving site-targeted cancer localization, drug delivery, therapeutic strategy, and disease pathways identification, rely on a precise understanding of biomarker kinetics, drug pharmacokinetics, and mechanistic behaviour of functionalized tracers through in vitro and in vivo studies. X-ray fluorescence (XRF) computed tomography (XFCT) offers a potential alternative to current 3D imaging techniques for spatiotemporal localization of nanoparticle-tracers with high spatial resolution and sensitivity. In this work, the applicability of a benchtop cone-beam system with a polychromatic X-ray source was examined with regard to physical constraints of engineered tissue models.Methods: A tissue engineering approach based on a decellularized scaffold was used to establish a 3D breast cancer model with MDA-MB-231 cells in co-culture with primary human fibroblasts. The 3D breast cancer system, in combination with small-animal-sized phantoms, was used to demonstrate the novel integrated pre-clinical imaging approach to perform in vitro surrogate investigations and non-destructive analysis on biophantoms. These models are adopted to evaluate the functionality and optimize the setup for high-spatial-resolution, fast, and fully-3D quantitative imaging. Polychromatic X-rays from a microfocus source are used for XRF stimulation from conventional Gadolinium (Gd) and nanoparticle-based Molybdenum (MoNPs) contrast agents.Results and Discussion: The intestinal scaffold allowed the invasion of the breast cancer cells over this barrier and therefore provides a valuable tool to study metastasis formation of tumor cells from epithelial origin. The breast cancer model was well suited for the development and validation of the proposed XRF imaging, with spatial resolution under <2 mm and contrast dose in the order of a few 100 μg/mL (∼0.3 mg/mL for Gd and ∼0.5 mg/mL for MoNPs), radiation dose in the order of a few 100 cGy (280 cGy for Gd and 94 cGy for MoNPs, with a possible reduction of an order of magnitude for Gd and 67% for MoNPs), and imaging time in the order of 10 min for Gd (33 min total) and 100 min (2.8 h total) for MoNPs, approaching in vivo conform conditions for pre-clinical studies. High-resolution XFCT for tissue-engineered cancer models would be of significant interest in biomedical research and diagnostic imaging, e.g., for an increased mechanistic understanding of molecular processes in tumor formation or early cancer detection.

Full-field in vivo imaging of nanoparticles using benchtop cone-beam XFCT system with pixelated photon counting detector

Objective. X-ray fluorescence computed tomography (XFCT) is a promising noninvasive technique for in vivo imaging of high-Z elements (e.g. gadolinium (Gd) or gold (Au)). In this study we upgraded our experimental XFCT system using a flat panel photon counting detector with redesigned pinhole collimation in order to achieve 3D XFCT images during one scan. Approach. Aiming at the characteristics of pinhole-collimated cone-beam XFCT imaging, a new scatter correction algorithm was proposed to estimate the normalized spectrum of scatter background based on K–N formula and realize correction by a weighted least squares method. Then, images were quantitatively reconstructed by a maximum likelihood iterative algorithm with the attenuation correction. Main results. The potential on full-field in vivo XFCT imaging of this new system was investigated. An imaging experiment of a PMMA phantom with the diameter of 35 mm was carried out for quantitative evaluation of the system performance. Results show that 2 mg ml−1 Gd solutions can be successfully reconstructed with a 45 min cone-beam XFCT scan. In vivo XFCT imaging experiments of mice with injection of Gd nanoparticles (GdNPs) were also performed and demonstrated in this paper. A mouse was injected through the tail vein with 20 mg ml−1 NaGdF4 solution and then anesthetized with isoflurane during the cone-beam XFCT scan. Significance. The distribution of the GdNPs inside the mouse can be well reconstructed so that the deposition of NPs in vivo can be clearly observed, which indicates the feasibility of the proposed system for full-field XFCT of small animals and further potential in relevant in vivo research.

Industrial Computed Tomography Technique Development for Industrial Volumetric X-Ray CT

It is often stated that no two engineers will set up an industrial X-ray computed tomography (CT) scan with the same parameters. In this article, an orderly set of steps is presented that will lead to an acceptable CT scan result for typical cone beam (volumetric) systems with application to denser and/or larger objects. This approach can be applied when using minifocus, mesofocus, and microfocus X-ray tubes. The strategy covers preparation and general considerations, selection of the proper tube and detector, methods to determine the proper magnification, setting X-ray tube and detector parameters, considerations to achieve good image quality, and common mistakes to avoid.

Cone-Beam Navigation Can Reduce the Radiation Exposure and Save Fusion Length-Dependent Operation Time in Comparison to Conventional Fluoroscopy in Pedicle-Screw-Based Lumbar Interbody Fusion.

This study investigates the advantages and disadvantages of cone-beam-based navigated standardized posterior lumbar interbody fusion surgery (PLIF), regarding the radiation exposure and perioperative time management, compared to the use of fluoroscopy. Patients treated receiving an elective one- to three-level PLIF were retrospectively enrolled in the study. The surgery time, preparation time, operation room time, and effective dose (mSv) were analyzed for comparison of the radiation exposure and time consumption between cone-beam and fluoroscopy; Results: 214 patients were included (108 cone-beam navigated, and 106 traditional fluoroscopies). Using cone-beam navigation, reductions in the effective dose (2.23 ± 1.96 mSv vs. 3.39 ± 2.32 mSv, p = 0.002) and mean surgery time of 30 min (143.62 ± 43.87 min vs. 171.10 ± 48.91 min, p < 0.001) were demonstrated, which leveled out the extended preparation time of 7–8 min (37.25 ± 9.99 min vs. 29.65 ± 7.69 min, p < 0.001). These effects were fusion length dependent and demonstrated additional benefits in multisegmental surgeries. The cone-beam navigation system led to a reduction in the perioperative time requirements and radiation exposure. Furthermore, the controversially discussed longer preparation time when using cone-beam navigation was amortized by a shortened surgery time, especially in multilevel surgery.

Cone-beam breast CT using an offset detector: effect of detector offset and image reconstruction algorithm

Objective. A dedicated cone-beam breast computed tomography (BCT) using a high-resolution, low-noise detector operating in offset-detector geometry has been developed. This study investigates the effects of varying detector offsets and image reconstruction algorithms to determine the appropriate combination of detector offset and reconstruction algorithm. Approach. Projection datasets (300 projections in 360°) of 30 breasts containing calcified lesions that were acquired using a prototype cone-beam BCT system comprising a 40 × 30 cm flat-panel detector with 1024 × 768 detector pixels were reconstructed using Feldkamp–Davis–Kress (FDK) algorithm and served as the reference. The projection datasets were retrospectively truncated to emulate cone-beam datasets with sinograms of 768 768 and 640 768 detector pixels, corresponding to 5 cm and 7.5 cm lateral offsets, respectively. These datasets were reconstructed using the FDK algorithm with appropriate weights and an ASD-POCS-based Fast, total variation-Regularized, Iterative, Statistical reconstruction Technique (FRIST), resulting in a total of 4 offset-detector reconstructions (2 detector offsets × 2 reconstruction methods). Signal difference-to-noise ratio (SDNR), variance, and full-width at half-maximum (FWHM) of calcifications in two orthogonal directions were determined from all reconstructions. All quantitative measurements were performed on images in units of linear attenuation coefficient (1/cm). Results. The FWHM of calcifications did not differ (P > 0.262) among reconstruction algorithms and detector formats, implying comparable spatial resolution. For a chosen detector offset, the FRIST algorithm outperformed FDK in terms of variance and SDNR (P < 0.0001). For a given reconstruction method, the 5 cm offset provided better results. Significance. This study indicates the feasibility of using the compressed sensing-based, FRIST algorithm to reconstruct sinograms from offset-detectors. Among the reconstruction methods and detector offsets studied, FRIST reconstructions corresponding to a 30 cm × 30 cm with 5 cm lateral offset, achieved the best performance. A clinical prototype using such an offset geometry has been developed and installed for clinical trials.

Super-resolution acquisition and reconstruction for cone-beam SPECT with low-resolution detector

Background and objectiveSingle-photon emission computed tomography (SPECT) imaging, which provides information that reflects the human body's metabolic processes, has unique application value in disease diagnosis and efficacy evaluation. The imaging resolution of SPECT can be improved by exploiting high-performance detector hardware, but this exploitation generates high research and development costs. In addition, the inherent hardware structure of SPECT requires the use of a collimator, which limits the resolution in SPECT. The objective of this study is to propose a novel super-resolution (SR) reconstruction algorithm with two acquisition methods for cone-beam SPECT with low-resolution (LR) detector. MethodsA SR algorithm with two acquisition methods is proposed for cone-beam SPECT imaging in the projection domain. At each sampling angle, multi LR projections can be obtained by regularly moving the LR detector. For the two proposed acquisition methods, we develop a new SR reconstruction algorithm. Using our SR algorithm, a SR projection with the corresponding sampling angle can be obtained from multi LR projections via multi-iterations, and then, the SR SPECT image can be reconstructed. The peak signal-to-noise ratio (PSNR), structural similarity index measure (SSIM), signal-to-noise ratio (SNR) and contrast recovery coefficient (CRC) are used to evaluate the final reconstruction quality. ResultsThe simulation results obtained under clean and noisy conditions verify the effectiveness of our SR algorithm. Three different phantoms are verified separately. 16 LR projections are obtained at each sampling angle, each with 32 × 32 bins. The high-resolution (HR) projection has 128 × 128 bins. The reconstruction result of the SR algorithm obtains an evaluation value that is almost the same as that of the HR reconstruction result. Our results indicate that the resolution of the resulting SPECT image is almost four times higher. ConclusionsThe authors develop a SR reconstruction algorithm with two acquisition methods for the cone-beam SPECT system. The simulation results obtained in clean and noisy environments prove that the SR algorithm has potential value, but it needs to be further tested on real equipment.

ASME B89.4.23 Performance Evaluation Tests and Geometry Errors in X-Ray Computed Tomography Systems.

A documentary standard produced by the American Society of Mechanical Engineers (ASME) for performance evaluation of industrial X-ray computed tomography (XCT) systems for dimensional measurements was released in early 2021. This standard, ASME B89.4.23-2020, specifies test procedures that may be performed to determine whether a system meets the manufacturer's accuracy specifications for acceptance before or after purchase, or for periodic reverification. While there are some core testing requirements in the standard, there is also some flexibility, allowing for a variety of testing configurations that meet the requirements of the standard. It is important that the chosen testing configuration be sensitive to the different systematic sources of error in XCT systems to provide confidence that the system will meet the manufacturer's accuracy specifications for measurements performed by the user subsequent to testing. In this paper, we provide guidance on how to optimally apply the ASME 89.4.23 standard in industry to achieve high sensitivity to geometry errors in cone-beam XCT systems. Through simulation studies, we present some examples of testing configurations that meet the requirements of the ASME B89.4.23 standard and discuss their sensitivity to geometry errors of the detector and the rotation stage. We show that there are some testing configurations that achieve maximal sensitivity to these errors, while other configurations do not capture these error sources with adequate sensitivity.

A geometric calibration approach for an industrial cone-beam CT system based on a low-rank phantom

Precise alignment of the system scan geometry is crucial to ensure the reconstructed image quality in a cone-beam computed tomography (CT) system. A calibration method that depends on the local features of a multi-sphere phantom is probably affected by local image variations. In addition, multiple projections with circular scanning are usually required by this type of method to derive misaligned parameters. In contrast to previous works, this paper proposes a method that depends on the global symmetric low-rank feature of a novel phantom, which can accurately represent the system geometrical misalignment. All the misaligned parameters of the cone-beam CT system can be estimated from a single perspective direction without circular scanning. Meanwhile, since the global low-rank feature of the phantom is utilized, the proposed method is robust to noise. We study the performance of the proposed method through simulations and real experiments. The experimental results demonstrate that the proposed method can estimate the system geometric parameters accurately, leading to superior image quality, with the modulation transfer function of our method (0.22) higher than that of the competing method (0.13) at the spatial resolution of 10 lp mm−1.

Bias-voltage dependent operational characteristics of a fully spectroscopic pixelated cadmium telluride detector system within an experimental benchtop x-ray fluorescence imaging setup

Commercially available fully spectroscopic pixelated cadmium telluride (CdTe) detector systems have been adopted lately for benchtop x-ray fluorescence (XRF) imaging/computed tomography (XFCT) of objects containing metal nanoprobes such as gold nanoparticles (GNPs). To date, however, some important characteristics of such detector systems under typical operating conditions of benchtop XRF/XFCT imaging systems are not well known. One important but poorly studied characteristic is the effect of detector bias-voltage on photon counting efficiency, energy resolution, and the resulting material detection limit. In this work, therefore, we investigated these characteristics for a commercial pixelated detector system adopting a 1-mm-thick CdTe sensor (0.25-mm pixel-pitch), known as HEXITEC, incorporated into an experimental benchtop cone-beam XFCT system with parallel-hole detector collimation. The detector system, operated at different bias-voltages, was used to acquire the gold XRF/Compton spectra from 1.0 wt% GNP-loaded phantom irradiated with 125 kVp x-rays filtered by 1.8-mm Tin. At each bias-voltage, the gold XRF signal, and the full-width-at-half-maximum at gold Kα 2 XRF peak (∼67 keV) provided photon counting efficiency and energy resolution, respectively. Under the current experimental conditions, the detector photon counting efficiency and energy resolution improved with increasing bias-voltage by ∼41 and ∼29% at −300V; ∼54 and ∼35% at −500V, respectively, when compared to those at −100V. Consequently, the GNP detection limit improved by ∼26% at −300V and ∼30% at −500V. Furthermore, the homogeneity of per-pixel energy resolution within the collimated detector area improved by ∼34% at −300V and ∼54% at −500V. These results suggested the gradual improvements in the detector performance with increasing bias-voltage up to −500V. However, at and beyond −550V, there were no discernible improvements in photon counting efficiency and energy resolution. Thus, the bias-voltage range of −500 to −550V was found optimal under the current experimental conditions that are considered typical of benchtop XRF/XFCT imaging tasks.

THE COMBINATION OF SHAPE SENSING ROBOTIC BRONCHOSCOPY WITH MOBILE 3D IMAGING TO VERIFY TOOL-IN-LESION AND ASSESS DIVERGENCE

TOPIC: Procedures TYPE: Late Breaking PURPOSE: With recent advances in robotic bronchoscopy for peripheral pulmonary nodule sampling, there has been notable improvements in reach, stability, and precision. However, barriers such as CT to body divergence and sampling error remain. Traditional cone beam systems have been shown to overcome these hurdles, however, this imaging modality is expensive and can have limited availability. The combination of shape-sensing robotic bronchoscopy (SSRAB) and mobile C-arm with CT capabilities could not only enhance the confidence of the pathology results with confirmation of tool-in-lesion for peripheral pulmonary nodules but may also overcome diaphragmatic motion through real-time 3D image feedback to make precise micro-adjustments and optimize outcomes in a transportable fashion. METHODS: A single-center prospective study was conducted to evaluate the combined use of SSRAB with portable cone beam computed tomography to visualize tool-in-lesion as a correlate to diagnostic yield (NCT# 04740047). Fluoroscopy and radiation data were captured. Additionally, data regarding nodule motion during navigation and breath holds were captured to quantify nodule motion and divergence. RESULTS: Twenty-two lesions were captured in 12 males (54.5%) and 10 females (45.5%). The median lesion size was 15 mm (range 10 – 27 mm) with the median airway generation being 7 (range 5-11) and median distance from pleura of 13 mm (range 1 - 45.8 mm). Most lesions were in the left upper lobe (8, 34.8%). Tool-in-lesion was visualized at the time of the procedure in 21 lesions (95.5%). Based on immediate histopathologic review, 14 (63.63%) nodules were malignant and 6 (27.3%) were benign. Two specimens were suggestive of inflammation and are awaiting follow up imaging. Mean number of spins was 2.6 (± 1.8 spins) with a mean fluoroscopy time of 9.1 minutes (± 6.6 minutes) and a mean Dose Area Product of 51.1 Gy*cm2 (± 33.9 Gy*cm2). There were no episodes of bleeding or pneumothorax. Observed CT-body divergence was overcome using the combination of both technologies as evidenced by the tool-in-lesion rate and will be quantified when the entire dataset is available. CONCLUSIONS: The combination of SSRAB and mobile 3D imaging allows for adequate visualization of tool in lesion without the need for a fixed cone beam CT and may improve diagnostic yield. CLINICAL IMPLICATIONS: Shape-sensing robotic technology combined with mobile CT imaging allows for accurate placement of the biopsy tool in the lesion. This combination may enhance diagnostic ability for sampling of peripheral pulmonary nodules and translate well in the applications of therapeutics in the future. Mobile 3D imaging allows for flexibility and maneuverability without the need for an expensive fixed cone beam CT room with adequate image quality. DISCLOSURES: No relevant relationships by Jennifer Duke, source=Web Response No relevant relationships by Eric Edell, source=Web Response No relevant relationships by Sebastian Fernandez-Bussy, source=Web Response No relevant relationships by Ryan Kern, source=Web Response Research grant relationship with Intuitive Surgical Please note: $5001 - $20000 by Janani Reisenauer, source=Web Response, value=Grant/Research Support

Tetrahedron beam imaging with a multi-pixel thermionic emission X-ray source and a photon-counting detector: A benchtop experimental study.

A tetrahedron beam (TB) X-ray system with a linear X-ray source array and a linear detector array positioned orthogonal to each other may overcome the X-ray scattering problem of traditional cone-beam X-ray systems. We developed a TB imaging benchtop system using a linear array X-ray source to demonstrate the principle and benefits of TB imaging. A multi-pixel thermionic emission X-ray (MPTEX) source with 48 focal spots in 4-mm spacing was developed in-house. The X-ray beams are collimated to a stack of fan beams that are converged to a 6-mm wide multi-row photon-counting detector (PCD). The data collected with a sequential scan of the sources at a fixed view angle were synthesized to a 2D radiography image by a shift-and-add algorithm. The data collected with a full rotation of the system were reconstructed into 3D TB CT (TBCT) images using an Feldkamp, Davis, and Kress (FDK)-based computed tomography (CT) algorithm modified for the TB geometry. With an 18.8-cm long source array and a 35-cm long detector array, the TB benchtop system provides a 25-cm cross-sectional and 8-cm axial field of view (FOV). The scatter-to-primary ratio (SPR) was approximately 17% for TB, as compared with 120% for cone beam geometry. The TBCT system enables reconstructions in two-dimensional radiography and three-dimensional volumetric CT. The TBCT images were free of "cupping" artifacts and have similar image quality as diagnostic helical CT. A TB imaging benchtop imaging system was successfully developed with MPTEX source and PCD. Phantom and animal cadaver imaging demonstrated that the TB system can produce satisfactory radiographic X-ray images and 3D CT images with image quality comparable to diagnostic helical CTs.

Lumbar hemivertebra resection in congenital scoliosis utilizing cone-beam navigation: less radiation, more accuracy\u2014proof of concept

PurposeTo present the first known pediatric utilization of cone-beam navigation system (CBNS) for hemivertebra resection and spondylodesisCase presentationA 14-year-old female with congenital scoliosis, diagnosed at 8 years of age, presenting with progressive symptoms, a Cobb angle (L3-5) of 38° at time of surgery, treated historically with conservative measures. Presence of spinal intramedullary disease was excluded prior to operation via whole spine MRI.ResultsPatient successfully underwent surgical correction utilizing the CBNS (O-arm™, Medtronic®). Post-operative Cobb angle (L3-5) was restored to 8°. Following four different pediatric patient’s radiation exposures (two receiving correction via the O-arm platform and two via the traditional method employing fluoroscopy), we show a reduction in radiation exposure using the CBNS system.ConclusionWe present the first known pediatric case of the utilization of the CBNS system for hemivertebra correction. We demonstrate that utilizing the CBNS platform can not only increase surgical accuracy but also decrease pediatric patient’s radiation exposure as a preoperative CT scan is not needed. Future studies should continue to explore additional benefits of implementing the system into surgical practice.

Characterization of a Pixelated Cadmium Telluride Detector System Using a Polychromatic X-Ray Source and Gold Nanoparticle-Loaded Phantoms for Benchtop X-Ray Fluorescence Imaging.

Pixelated semi-conductor detectors providing high energy resolution enable parallel acquisition of x-ray fluorescence (XRF) signals, potentially leading to performance enhancement of benchtop XRF imaging or computed tomography (XFCT) systems utilizing ordinary polychromatic x-ray sources. However, little is currently known about the characteristics of such detectors under typical operating conditions of benchtop XRF imaging/XFCT. In this work, a commercially available pixelated cadmium telluride (CdTe) detector system, HEXITEC (High Energy X-ray Imaging Technology), was characterized to address this issue. Specifically, HEXITEC was deployed into our benchtop cone-beam XFCT system, and used to detect gold Kα XRF photons from gold nanoparticle (GNP)-loaded phantoms. To facilitate the detection of XRF photons, various parallel-hole stainless steel collimators were fabricated and coupled with HEXITEC. A pixel-by-pixel spectrum merging algorithm was introduced to obtain well-defined XRF + scatter spectra with parallel-hole collimators. The effect of charge sharing addition (CSA) and discrimination (CSD) algorithms was also investigated for pixel-level CS correction. Finally, the detector energy resolution, in terms of the full-width at half-maximum (FWHM) values at two gold Kα XRF peaks (~68 keV), was also determined. Under the current experimental conditions, CSD provided the best energy resolution of HEXITEC (~1.05 keV FWHM), compared with CSA and no CS correction. This FWHM value was larger (by up to ~0.35 keV) than those reported previously for HEXITEC (at ~60 keV Am-241 peak) and single-crystal CdTe detectors (at two gold Kα XRF peaks). This investigation highlighted characteristics of HEXITEC as well as the necessity for application-specific detector characterization.

Deviation of dental implants placed using a novel 3D-printed surgical guide: An in vitro study.

There is very little literature available on the reliability of the rapid prototyping technology in the production of three-dimension (3D)-printed surgical guides for accurate implant placement. The aim of the study was to evaluate the deviation of implant placement performed with a surgical guide fabricated by means of the rapid prototyping technique (the PolyJet™ technology). Twenty sheep mandibles were used in the study. Pre-surgical cone-beam computed tomography (CBCT) scans were acquired for the mandibles by using the Kodak 9000 3D cone-beam system. Two implants with dimensions of 4 mm in diameter and 10 mm in length were virtually planned on the 3D models of each mandible by using the Mimics software, v. 16.0. Twenty surgical guides were designed and printed using the PolyJet technology. A total of 40 implants were placed using the surgical guides, 1 on each side of the mandible (2 implants per mandible). The post-surgical CBCT scans of the mandibles were performed and superimposed on the pre-surgical CBCT scans. The amount of deviation between the virtually planned placement and the actual implant placement was measured, and a descriptive analysis was done. The results showed that the mean deviation at the implant coronal position was 1.82 ±0.74 mm, the mean deviation at the implant apex was 1.54 ±0.88 mm, the mean depth deviation was 0.44 ±0.32 mm, and the mean angular deviation was 3.01 ±1.98°. The deviation of dental implant placement performed with a 3D-printed surgical guide (the PolyJet technology) is within the acceptable 2-millimeter limit reported in the literature.

Sparse-view, short-scan, dedicated cone-beam breast computed tomography: image quality assessment

The purpose of this study is to quantify the impact of sparse-view acquisition in short-scan trajectories, compared to 360-degrees full-scan acquisition, on image quality measures in dedicated cone-beam breast computed tomography (BCT). Projection data from 30 full-scan (360-degrees; 300 views) BCT exams with calcified lesions were selected from an existing clinical research database. Feldkamp-Davis-Kress (FDK) reconstruction of the full-scan data served as the reference. Projection data corresponding to two short-scan trajectories, 204 and 270-degrees, which correspond to the minimum and maximum angular range achievable in a cone-beam BCT system were selected. Projection data were retrospectively sampled to provide 225, 180, and 168 views for 270-degrees short-scan, and 170 views for 204-degrees short-scan. Short-scans with 180 and 168 views in 270-degrees used non-uniform angular sampling. A fast, iterative, total variation-regularized, statistical reconstruction technique (FIRST) was used for short-scan image reconstruction. Image quality was quantified by variance, signal-difference to noise ratio (SDNR) between adipose and fibroglandular tissues, full-width at half-maximum (FWHM) of calcifications in two orthogonal directions, as well as, bias and root-mean-squared-error (RMSE) computed with respect to the reference full-scan FDK reconstruction. The median values of bias (8.6 × 10−4–10.3 × 10−4 cm−1) and RMSE (6.8 × 10−6–9.8 × 10−6 cm−1) in the short-scan reconstructions, computed with the full-scan FDK as the reference were close to, but not zero (P < 0.0001, one-sample median test). The FWHM of the calcifications in the short-scan reconstructions did not differ significantly from the reference FDK reconstruction (P > 0.118), except along the superior-inferior direction for the short-scan reconstruction with 168 views in 270-degrees (P = 0.046). The variance and SDNR from short-scan reconstructions were significantly improved compared to the full-scan FDK reconstruction (P < 0.0001). This study demonstrates the feasibility of the short-scan, sparse-view, compressed sensing-based iterative reconstruction. This study indicates that shorter scan times and reduced radiation dose without sacrificing image quality are potentially feasible.

Investigations on the buckling and dynamics of diving-inspired systems when entering water

This work provides comparative modeling approaches to determine the velocities and natural frequencies of plunge-diving bird and bioinspired drone systems when entering water. These systems are chosen to further explain the survival of diving birds as they impact water and to provide insight into the design geometry and material choice of bioinspired diving drones. A nonlinear reduced-order model is developed and utilized to analyze the dive at impact considering both Timoshenko and Euler–Bernoulli beam theories. Using Hamilton’s principle, the equations of motion are first derived. Then, static and dynamic buckling analyses are conducted. For this study, a geometrically simplified cone-beam system is considered, where the cone represents the head and the beam represents both the neck and body of the plunge-diving systems. The first study is to analyze the effects different diving drone materials and cone dimensions play on the sensitivity of the system. The second study applies geometric parameters to the cone-beam system representative of a plunge-diving bird (Northern gannet) and a surface-diving bird (Double-crested cormorant). The results show that choosing a material with a higher Young’s modulus and a cone with a smaller half angle increase the velocity at which buckling occurs. The buckling velocities of the predicted Northern gannet model appear to be much greater than the average recorded diving speeds, suggesting that the bird is capable of plunge-diving at more extreme conditions. The natural frequencies are found for the aforementioned plunge-diving systems to predict failure if any external frequencies are known to act on the system while on a mission, such as conditions dependent on the climate or environment. It is shown in all buckling studies that the Euler-Bernoulli beam theory consistently overestimates the responses when compared with the Timoshenko beam theory. In the dynamic responses, Euler–Bernoulli beam theory overestimates for the pre-buckling region, then underestimates at the start of the post-buckling region until a point where the two theories cross paths. The amount of error with Euler–Bernoulli beam theory depends heavily on the slenderness ratio of the beam due to the theory being a simplification of the Timoshenko beam theory. It is noted that as the development of a more realistic bird model improves, the thickness will become significant and the use of Euler–Bernoulli beam theory at the point of impact will no longer be a valid assumption.

Image metrics for geometric calibration of a cone-beam tomographic X-ray system based on a single plastic brick

The exact knowledge of the geometric acquisition parameters directly influences the quality of a tomographic reconstruction. Most calibration procedures use calibration phantoms that consist of metal beads arranged in a specific order. If the exact positions of the metal beads are to be sufficiently known, the production of such calibration phantoms can become very expensive. To avoid this problem, we propose a method that uses single plastic bricks (e.g. LEGO bricks) as calibration phantom. Based on a CAD model, projections with given acquisition parameters are simulated and then compared to the real projection using a metric. The objective of our research is to evaluate which metrics are best suited for the comparison of such projections. The results of applying two metrics on simulated and real data are presented.

Spatial resolution of a laboratory based X-Ray cone-beam laminography scanning system for various trajectories

Computed laminography (CL), a long established NDT method, is ideal for the non-destructive evaluation of plate-like structures, for which conventional computed tomography (CT) is less well suited. This paper demonstrates the feasibility of implementing raster CL on a Nikon Metrology custom build X-ray CT scanner without the need for specialised equipment. To provide a more principled way to demonstrate the widespread adoption of CL for defect characterization in plate-like structures, a test specimen was designed and manufactured from Polyoxymethylene (Delrin) that allows well defined features of different size and orientation to be characterized. The study highlights the relation between direction-dependent spatial resolution, feature geometry and scan trajectory. It demonstrates that high-resolution and high-speed in situ volume-imaging of plate-like structures with large aspect ratios is viable at levels that would be challenging via CT or alternative three-dimensional NDT methods.