Cylindrical Scan Research Articles

Effect of shape and size of implant scan body on scanning accuracy: an in vitro study.

Objectives: Evaluating the effect of shape and size of implant scan body on the accuracy of optical 3D scanning. Materials and methods: Fifteen PEEK scan bodies were milled, including 1 spherical, 9 cylindrical, and 5 cuboidal. The 3D position and angulation of each scan body were measured using a CMM 3 times and a laboratory scanner 10 times. The linear and angular trueness and precision of the scans were calculated by comparing with the CMM measurements. Results: The linear accuracy of the cylindrical scan bodies (9.5±6.2 µm) was significantly higher than those of the cuboidal (17.7±8.1 µm) and spherical scan bodies (12.5±6.5 µm). The cuboidal (0.050±0.009°) showed significantly better angular accuracy than the cylindrical (0.065±0.040°). In the cylindrical group, the narrow (∅4.8 mm) demonstrated significantly inferior accuracy than the wider (∅5.5 mm and ∅6.5 mm)(p=0.003). The tall (12 mm) showed significantly higher angular trueness than the shorter (8 and 4 mm)(p<0.001). In the cuboidal group, the 24 mm2 exhibited significantly poorer angular trueness compared to the 18 mm2 and 30 mm2 (p<0.001) Conclusions: The shape and size of the implant scan body significantly affect the scanning accuracy. Spherical scan bodies cannot transfer implant angulation. Scan bodies with a size of >∅4.8mm and >8 mm seem accurate for transferring the 3D implant position. Clinical significance: The shape and size of scan bodies directly influence the accuracy of 3D scanning. Well-designed scan bodies offer better transfer results, which is crucial for ensuring passive fit of implant prostheses and improving long-term clinical outcomes.

Complete digital workflow for prosthesis prototype fabrication with double digital scanning: A retrospective study with 45 edentulous jaws.

To assess the accuracy of fit of complete-arch printed prosthesis prototypes generated with a digital workflow protocol for completely edentulous jaws. Forty-five edentulous jaws (35 patients) underwent intraoral complete-arch digital scans with the double digital scanning (DDS) technique and the generated standard tessellation language (STL) files were superimposed and imported into computer-aided design software. After STL merging, each master STL file was used for printing a prosthesis prototype. The primary outcome was the accuracy of fit assessment of the printed prototypes on verified master stone casts. Two experienced clinicians tested the accuracy of fit with radiographs and screw-resistance tests. Secondary outcomes were the effect of the scan body shape and implant number on the accuracy of fit. Out of the 45 DDS-generated prosthesis prototypes, 39 presented with accurate fit on verified master stone casts, yielding an 86.70% accuracy of fit. Cylindrical scan bodies led to 100% accuracy of fit (25/25), whereas polygonal scan bodies presented with 70% accuracy of fit (14/20). Four implant-supported prostheses yielded 100% accuracy of fit (12/12), compared with 25/29 (86.30%) accuracy of fit for the six-implant-supported ones. Fisher's exact test was used to assess the effect of different scan body shapes (p=0.005) and implant number on accuracy of fit. Chi-squared test was used to assess the association between the number of implants per arch and the accuracy of fit (p=0.039). Thirty-nine out of 45 complete-arch prosthesis prototypes generated with a completely digital workflow presented with clinically acceptable fit. The effect of the scan body design and implant number was statistically significant, favoring cylindrical scan bodies and four-implant-supported prostheses.

Detection of space-time clusters using a topological hierarchy for geospatial data on COVID-19 in Japan.

In this paper, we detected space–time clusters using data on coronavirus disease 2019 (COVID-19) collected daily by each prefecture in Japan. COVID-19 has spread globally since the first confirmed case in China, in December 2019. Several people have to date been infected in Japan since the first confirmed case in January 2020. The outbreak of COVID-19 has had a significant impact on many people’s lives. Studies are being conducted to detect regions, called clusters, which pose a significantly higher risk of infection than their surrounding areas, based on a spatial scan statistics of COVID-19 infections. Among these studies, space–time cluster detection has to date been actively performed to gain knowledge regarding infection status. Based on the spatial scan statistic, the cylindrical scan method is a widely used space–time cluster detection method. This method enables concurrent detection of the location and time of a cluster occurrence. However, this method cannot capture spatial changes in a cluster over time. When applying the existing method to a cluster whose shape changes over time, the number of calculations required becomes extremely large, and the analysis may become difficult. In this study, we focused on the hierarchical structure of the data obtained by conducting an echelon analysis and applied the space–time cluster detection method based on this structure to enable the capture of changes in a cluster’s shape. Furthermore, we visualized the location and period of a cluster’s occurrence and considered the cause of the cluster.

Trueness of ten intraoral scanners in determining the positions of simulated implant scan bodies

Few investigations have evaluated the 3-dimensional (3D) accuracy of digital implant scans. The aim of this study was to evaluate the performance of 10 intraoral scanners (IOSs) (CEREC Omnicam, CEREC Primescan, CS 3600, DWIO, i500, iTero Element, PlanScan, Trios 2, Trios 3, and True Definition) in obtaining the accurate positions of 6 cylinders simulating implant scan bodies. Digital scans of each IOS were compared with the reference dataset obtained by means of a coordinate measuring machine. Deviation from the actual positions of the 6 cylinders along the XYZ axes and the overall 3D deviation of the digital scan were calculated. The type of IOSs and position of simulated cylindrical scan bodies affected the magnitude and direction of deviations on trueness. The lowest amount of deviation was found at the cylinder next to the reference origin, while the highest deviation was evident at the contralateral side for all IOSs (p < 0.001). Among the tested IOSs, the CEREC Primescan and Trios 3 had the highest trueness followed by i500, Trios 2, and iTero Element, albeit not statistically significant (p > 0.05), and the DWIO and PlasScan had the lowest trueness in partially edentulous mandible digital implant scans (p < 0.001).

Evaluation of Reconstruction Methodology for Helical Scan Guided Photoacoustic Endoscopy.

Photoacoustic endoscopy (PAE), combining both advantages of optical contrast and acoustic resolution, can visualize the chemical-specific optical information of tissues inside human-body. Recently, its corresponding reconstruction methods have been extensively researched. However, most of them are limited on cylindrical scan trajectories, rather than a helical scan which is more clinically practical. On this note, this article proposes a methodology of imaging reconstruction and evaluation for helical scan guided PAE. Different from traditional reconstruction method, synthetic aperture focusing technique (SAFT), our method reconstructs image using wavefield extrapolation which significantly improves computational efficiency and even takes only 0.25 seconds for 3-D reconstructions. In addition, the proposed evaluation methodology can estimate the resolutions and deviations of reconstructed images in advance, and then can be used to optimize the PAE scan parameters. Groups of simulations as well as ex-vivo experiments with different scan parameters are provided to fully demonstrate the performance of the proposed techniques. The quantitatively measured angular resolutions and deviations agree well with our theoretical derivation results D√{rs2 +h2} / [1.25(rs rd +h2)] (rad) and -h l / (rs rd +h2) (rad), respectively D,rd, rs,h and l represent transducer diameter, radius of scan trajectory, radius of source position, unit helical pitch and the distance from targets to helical scan plane, respectively). This theoretical result also suits for circular and cylindrical scan in case of h = 0 .

Three-Dimensional Imaging of Spinning Space Debris Based on the Broadband Radar

The rising population of space debris poses an enormous threat to all space vehicles, including space shuttles and other spacecraft with operators aboard; and their detection, tracking, and identification are of great importance. Using the spinning motion and the translational motion component that is parallel to its major axis, we have established a 3-D spiral synthetic aperture radar (SAR) imaging geometry and its corresponding signal model for space debris in this letter. Spatial offsets and coupling in the along-track and altitude directions, caused by the spiral motion of the radar, are compensated in the frequency domain. With these compensation procedures, the spiral SAR is simplified as a cylindrical scan mode. Then, a 3-D wavenumber domain algorithm is proposed to realize coherent imaging. The real data processing results are presented to demonstrate the effectiveness of the proposed algorithm for imaging space debris.

Spherical Wave Based Macromodels for Efficient System-Level EMC Analysis in Circuit Simulators Part II: Optimized Calculation of DUT–DUT Interactions

In this second part of two papers, the framework presented in Part I is extended with optimized routines that enable one to evaluate interactions between several devices under test (DUTs) through free space inside a circuit simulator environment, aimed at efficient system-level electromagnetic compatibility (EMC) analysis. Using a generalized scattering matrix formulation and an extensive understanding of the underlying theory of spherical wave expansions (SWEs), it is shown that the presented routines only add negligible computational cost to traditional scattering parameter simulations. The latter is obtained on the one hand by optimally truncating SWE based macromodels as described in Part I and on the other hand by observing that both near- and far-field interactions are only determined by a subset of parameters in the models. Therefore, this paper derives guidelines on the number of parameters needed to assure accurate simulations and validates them using two applications: 1) computing the radiated coupling between two DUTs; and 2) extending the first example in order to simulate efficiently a cylindrical scan of a DUT by an arbitrary measurement antenna.

Synthetic aperture imaging for multilayer cylindrical object using an exterior rotating transducer.

The synthetic aperture focusing technique (SAFT) with significant improvements in lateral resolution has been adapted for ultrasound imaging of multilayer objects. To apply SAFT to imaging of cylindrical objects such as solid axles or pipes with small diameter, exterior cylindrical scan is much preferred. In this paper, a frequency-domain algorithm is proposed for such cylindrical scan performed with an exterior rotating transducer. The algorithm is derived from Fourier-domain solutions to the waveequation in cylindrical coordinates, and then extended to the multilayer case. A simulation model for multilayer structure is established, and the algorithm is demonstrated for both simulated and experimental data. Compared with the raw images, the reconstructed images with proposed algorithm attain better lateral resolution for multilayer objects. It is shown that the attainable angular resolution for each layer is approximately consistent with that achieved in the single-layer case, as long as the transmission factors are approximately uniform within the divergence angle of the transducer. The performance of proposed algorithm is verified with experimental C-scan image and demonstrates that it is capable of improving the lateral resolution in both scanning directions.

Accuracy of two digital implant impression systems based on confocal microscopy with variations in customized software and clinical parameters.

To evaluate the accuracy of two digital impression systems based on the same technology but different postprocessing correction modes of customized software, with consideration of several clinical parameters. A maxillary master model with six implants located in the second molar, second premolar, and lateral incisor positions was fitted with six cylindrical scan bodies. Scan bodies were placed at different angulations or depths apical to the gingiva. Two experienced and two inexperienced operators performed scans with either 3D Progress (MHT) or ZFX Intrascan (Zimmer Dental). Five different distances between implants (scan bodies) were measured, yielding five data points per impression and 100 per impression system. Measurements made with a high-accuracy three-dimensional coordinate measuring machine (CMM) of the master model acted as the true values. The values obtained from the digital impressions were subtracted from the CMM values to identify the deviations. The differences between experienced and inexperienced operators and implant angulation and depth were compared statistically. Experience of the operator, implant angulation, and implant depth were not associated with significant differences in deviation from the true values with both 3D Progress and ZFX Intrascan. Accuracy in the first scanned quadrant was significantly better with 3D Progress, but ZFX Intrascan presented better accuracy in the full arch. Neither of the two systems tested would be suitable for digital impression of multiple-implant prostheses. Because of the errors, further development of both systems is required.

A Clinical Protocol for Intraoral Digital Impression of Screw-Retained CAD/CAM Framework on Multiple Implants Based on Wavefront Sampling Technology

To obtain an accurate CAD/CAM metal framework over 6 implants using a Chairside Intraoral Scanner based on the principle of active (optical) wavefront sampling. Six prototype cylindrical scan bodies screwed in the implants were used to obtain an intraoral digital impression. A conventional resin tooth try-in was fabricated and digitized with an extraoral scanner, and this dataset was merged to the digital data obtained from the intraoral impression to calculate the best framework design with advanced CAD software. The framework was fabricated with a 5-axis computer numerical control milling unit. Three clinical tests (saliva intrusion, Sheffield test, and screw resistance test) were performed to assess the fit of the framework. Under 3 clinical tests, an accurate fit was observed. The case presented in this report proposes a new clinical protocol for obtaining accurate digital impressions of multiple implants.

Real-time reconstruction of three-dimensional cylindrical near-field radar images using a single instruction multiple data interpolation approach

During the last decade, radar imaging has been used in near-field scenarios where a cylindrical scan geometry is required to properly illuminate the scan region, such as breast microwave radar imaging and microwave wood inspection. Nevertheless, current cylindrical near-field radar image formation algorithms are not fast enough to provide the throughput required by these novel applications. A real-time wavefront reconstruction approach for the formation of three-dimensional cylindrical near-field radar images is proposed in this study. This technique parallelises the mapping procedures during the reconstruction process in order to increase its computational efficiency. To further reduce the execution time of the proposed approach, it was implemented in a general purpose graphic processing unit in order to take advantage of the computing capabilities of this platform. The proposed method yielded accurate results when applied to simulated and experimental data sets and yielded speed improvements of two orders of magnitude compared to conventional cylindrical near-field radar reconstruction approaches.

SU-E-J-01: Analysis of Acquisition Parameters That Caused Artifacts in Four-Dimensional (4D) CT Images of Targets Undergoing Regular Motion.

The aim of this study was to clarify the impacts of acquisition parameters on artifacts in four-dimensional computed tomography (4D CT) images, such as the partial volume effect (PVE), partial projection effect (PPE), and mis-matching of initial motion phases between adjacent beds (MMimph) in cine mode scanning. A thoracic phantom and two cylindrical phantoms (2 cm diameter and heights of 0.5 cm for No. 1 and 10 cm for No.2) were scanned using 4D CT. For the thoracic phantom, acquisition was started automatically in the first scan with 5 sec and 8 sec of gantry rotation, thereby allowing a different phase at the initial projection of each bed. In the second scan, the initial projection at each bed was manually synchronized with the inhalation phase to minimize the MMimph. The third scan was intentionally un-synchronized with the inhalation phase. In the cylindrical phantom scan, one bed (2 cm) and three beds (6 cm) were used for 2 and 6 sec motion periods. Measured target volume to true volume ratios (MsTrueV) were computed. The relationships among MMimph, MsTrueV, and velocity were investigated. In the thoracic phantom, shorter gantry rotation provided more precise volume and was highly correlated with velocity when MMimph was minimal. MMimph reduced the correlation. For moving cylinder No. 1, MsTrueV was correlated with velocity, but the larger MMimph for 2 sec of motion removed the correlation. The volume of No. 2 was similar to the static volume due to the small PVE, PPE, and MMimph. Smaller target velocity and faster gantry rotation resulted in a more accurate volume description. The MMimph was the main parameter weakening the correlation between MsTrueV and velocity. Without reducing the MMimph, controlling target velocity and gantry rotation will not guarantee accurate image presentation given current 4D CT technology.

EVALUATION OF THE FAR FIELD RADIATED BY LONG ANTENNAS DIRECTLY FROM DATA ACQUIRED THROUGH A FAST HELICOIDAL SCANNING

A direct near-fleld-far-fleld transformation with helicoidal scanning for electrically long antennas is proposed in this paper. Such a transformation, which allows the evaluation of the antenna far fleld in any cut plane directly from the acquired near-fleld data without interpolating them, relies on the nonredundant sampling representation of electromagnetic flelds and makes use of a prolate ellipsoidal modelling of the antenna under test for determining the number of helix turns, whereas the number of samples on each of them is flxed by the minimum cylinder rule, as in the classical cylindrical scan. Numerical and experimental tests assessing the efiectiveness of the approach are shown.

Experimental validation of the NF–FF transformation with cylindrical scan from nonuniformly distributed data

AbstractThe article concerns the experimental validation of two techniques for compensating the probe positioning errors in a near‐field–far‐field transformation with cylindrical scan using a nonredundant number of measurements.The former uses the singular value decomposition method and can be applied when the irregularly acquired samples lie on nonuniform rings, thus allowing to reduce the starting two‐dimensional problem into two independent one‐dimensional ones. The latter, based on an iterative technique, can be employed also when the previous hypothesis does not hold but requires the existence of a one‐to‐one correspondence, associating at each uniform sampling point the nearest irregular one. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:915–920, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25847

Experimental Results Validating the Near-Field to Far-Field Transformation Technique with Helicoidal Scan

This paper concerns the experimental validation of the near-field - far-field transformation technique with heli- coidal scanning. Such a technique, based on the theoretical results concerning the nonredundant sampling representations of the electromagnetic fields, makes use of a two-dimensional optimal sampling interpolation formula to reconstruct the near-field data needed to perform the classical near-field - far-field transformation with cylindrical scan. The comparison of the far-field patterns reconstructed from the acquired helicoidal measurements with those obtained from the data di- rectly measured on the classical cylindrical grid assesses the effectiveness of the near-field - far-field transformation us- ing this innovative scanning technique. Its validity is further confirmed by the very good agreement with the direct far- field measurements.

LABORATORY TESTS ASSESSING THE EFFECTIVENESS OF THE NF-FF TRANSFORMATION WITH HELICOIDAL SCANNING FOR ELECTRICALLY LONG ANTENNAS

This paper deals with the experimental validation of an efiective near-fleld-far-fleld transformation technique with helicoidal scanning particularly suitable for electrically long antennas, whose validity has been numerically assessed in a previous authors' paper. Such a technique relies on the results relevant to the nonredundant sampling representations of the electromagnetic flelds and makes use of an optimal sampling interpolation algorithm, which allows the reconstruction of the near-fleld data needed by the near-fleld-far-fleld transformation with cylindrical scan. The use of a prolate ellipsoid instead of a sphere to model an elongated antenna allows one to consider measurement cylinders with a diameter smaller than the antenna height, thus reducing the error related to the truncation of the scanning zone. Moreover, a signiflcant reduction of the needed near- fleld data is also obtained. The comparison of the far-fleld patterns reconstructed from the acquired helicoidal measurements with those obtained from the data directly measured on the classical cylindrical grid assesses the efiectiveness of the near-fleld-far-fleld transformation using this innovative scanning technique. At last, its validity is further conflrmed by the very good agreement with the direct far-fleld measurements.

A Wavefront Reconstruction Method for 3-D Cylindrical Subsurface Radar Imaging

In recent years, the use of radar technology has been proposed in a wide range of subsurface imaging applications. Traditionally, linear scan trajectories are used to acquire data in most subsurface radar applications. However, novel applications, such as breast microwave imaging and wood inspection, require the use of nonlinear scan trajectories in order to adjust to the geometry of the scanned area. This paper proposes a novel reconstruction algorithm for subsurface radar data acquired along cylindrical scan trajectories. The spectrum of the collected data is processed in order to locate the spatial origin of the target reflections and remove the spreading of the target reflections which results from the different signal travel times along the scan trajectory. The proposed algorithm was successfully tested using experimental data collected from phantoms that mimic high contrast subsurface radar scenarios, yielding promising results. Practical considerations such as spatial resolution and sampling constraints are discussed and illustrated as well.

A flexibly shaped space-time scan statistic for disease outbreak detection and monitoring

BackgroundEarly detection of disease outbreaks enables public health officials to implement disease control and prevention measures at the earliest possible time. A time periodic geographical disease surveillance system based on a cylindrical space-time scan statistic has been used extensively for disease surveillance along with the SaTScan software. In the purely spatial setting, many different methods have been proposed to detect spatial disease clusters. In particular, some spatial scan statistics are aimed at detecting irregularly shaped clusters which may not be detected by the circular spatial scan statistic.ResultsBased on the flexible purely spatial scan statistic, we propose a flexibly shaped space-time scan statistic for early detection of disease outbreaks. The performance of the proposed space-time scan statistic is compared with that of the cylindrical scan statistic using benchmark data. In order to compare their performances, we have developed a space-time power distribution by extending the purely spatial bivariate power distribution. Daily syndromic surveillance data in Massachusetts, USA, are used to illustrate the proposed test statistic.ConclusionThe flexible space-time scan statistic is well suited for detecting and monitoring disease outbreaks in irregularly shaped areas.

Bistatic RCS Calculations From Cylindrical Near-Field Measurements—Part I: Theory

A theory is presented for computing scattered far fields of targets from cylindrical near-field measurements. The targets are illuminated by plane waves and measured in a radio anechoic chamber on a cylindrical scan surface. The scattered field on the scan cylinder is obtained by background subtraction. The near-field data is truncated at the top, bottom, and angular edges of the scan cylinder. These truncation edges can cause inaccuracies in the computed far fields. Correction techniques are developed for the top and bottom truncation edges. The cylindrical wave expansions automatically apply angular tapers to the near-field data that reduce the effect of the angular truncation edges. The taper functions depend on the angular sample spacing and are related to the currents induced on perfectly electrically conducting PEC cylinders in related scattering problems. The method of stationary phase is employed with asymptotic expressions for the taper functions to determine the area on the scan cylinder that is most important for computing the far field in a given direction. The theory is validated through numerical examples involving electrically large scatterers. The edge-correction techniques significantly increase the accuracy of the computed far field. A companion paper presents experimental results

A structured light-based system for human heads

The 3-D modeling of heads by using optical triangulation techniques is of great interest in the context of virtual reality, telecommunication and computer animation. This paper presents a structured light-based system mainly for human heads. It is named “3-D Laser Color Scanner” (3DLCS). A 3-D model is obtained with a cylindrical scan. The laser beam is switched on and off using a “light valve” and two successive CCD frames are captured, one with the laser line showing and one without. We can simplify the laser line extracting by subtracting these two images. In this system, two CCD cameras are used to avoid occlusion problems. Color information is read from the CCD when the laser light is absent. Since traditional laser scanner will miss the range data in the low-reflectance areas such as the hair area of human head, a shape from silhouette algorithm is presented to overcome this problem. Finally, we give some results using our system. The resulting model is suitable for many applications.