Smaller Voxel Size Research Articles

Comparison of CBCT with different voxel sizes and intraoral scanner for detection of periodontal defects: an in vitro study.

This study aimed to compare the diagnostic accuracy of cone beam CT (CBCT) units with different voxel sizes with the digital intraoral scanning technique in terms of the detection of periodontal defects. The study material comprised of 12 dry skulls with maxilla and mandible. Artificial defects were created on teeth separately using burs randomly on dry skulls. In total 46 dehiscences, 10 fenestrations, 17 furcations, 12 wall defects and 13 without periodontal defect were used in the study. Each tooth with and without defects was imaged at various vertical angles using each of the following modalities: a Veraviewepocs 3D R100 CBCT device and a 3D Shape TRIOSㄾ Color P13 Shade Intraoral Scanner. The κ values for interobserver agreement between observers ranged between 0.29 and 0.86 for the CBCT 10 × 8 cm field of view (FOV) with 0,160 mm3 voxel size; 0.35 and 1 for the CBCT 8 × 8 cm FOV with 0,125 mm3 voxel size; and 0.30 and 1 of intraoral scans. The κ values for detecting defects on anterior teeth were the least, following premolar and molar teeth both CBCT and intraoral scanning. Smaller voxel sizes and smaller CBCT FOV has the highest sensitivity and diagnostic accuracy for detecting various periodontal defects among the scanner modalities examined. Adequate evaluation of the condition of the alveolar bone and periodontal tissues is important for the diagnosis, treatment, and prognosis of periodontal disease. Limited examination methods, such as palpation, inspection, and periodontal probe examination, may provide insufficient information for the diagnosis of periodontal diseases.

Lightscaping

A collaboration of German researchers presents the first instance of two-photon polymerisation induced by a mode-locked diode laser system, with a pulse length of 440 fs. Two-photon polymerisation allows for the production of complex microstructures, usually using an expensive laser system, such as Ti:sapphire. The development presented here works using a much cheaper diode laser, significantly reducing the cost of the process. Around the turn of the millennium, the research area of multiphoton polymerisation became well established; in particular, a technique known as direct laser writing (DLW) was developed to more easily produce photonic crystals with a range of uses, from thin-film optics to colour changing paints to photonic circuits. DLW requires a photoresist (a light sensitive material) to be illuminated by laser light of a frequency below its single-photon polymerisation threshold. When the laser light is tightly focused inside the photoresist, the light intensity may exceed the threshold for initiating multiphoton polymerisation. Authors Gordon Zyla (left) and Nils Surkamp (right) in their lab. SEM overview image of the ‘winding tower’ structure. Two-photon polymerisation manufacturing process.The oil immersion objective focusses the incident laser beam into the photoresist. Three-dimensional structuring can be obtained by moving the focal spot relative to the droplet. The smallest polymerisation is defined by the voxel size, which depends on the structuring speed and intensity of the focal spot. The SEM image in A. shows the fabricated lines structures between two cuboids. The SEM image in B. shows the ‘winding tower’ structure. In the past 10 years this area of research has seen a resurgence in interest, primarily due to the increased capabilities of diode lasers. One of the main drawbacks of multiphoton polymerisation is that it requires a high-frequency laser that can operate in the femtosecond range. Traditionally, appropriate laser systems of this type are expensive, such as Ti:sapphire lasers or fibre lasers. However, we are now starting to see diode lasers that can reliably operate in the femtosecond range for a fraction of the operating costs of conventional systems. Surkamp et al., in their work published in Electronics Letters, propose using a mode-locked diode laser, capable of producing ultrashort laser pulses 440 fs in length. In their design, the laser outputs an impressive 160 mW per pulse. The mode-locked nature of the laser is what allows pulses to reach the 440 fs pulse length. A key characteristic of two-photon polymerisation is that it has a high resolution, in the order of sub-100 nm. The resolution depends on the ‘voxel size’ – voxels being a 3D analogue of pixels. Therefore, with a small voxel size, very fine structures can be produced. The structures are produced layer-by-layer, in a manner similar to conventional 3D printing techniques. The size of the voxel is dependent on the structuring velocity (the speed at which the structure is produced) and the focus intensity. Surkamp et al. produced two structures, the first being two cuboids, 4 micrometres apart, connected by a number of lines. The lines were produced at increasing velocities to test how the technique's resolution would cope at different speeds. The second structure was much more complex, a winding ‘tower’ with additional embellishment in the structure. The tower has a roof, with two angled supports, and a central post containing a winding ‘staircase’ running up it. The two structures were analysed using a scanning electron microscope and look fantastic. The results clearly show the suitability of two-photon polymerisation as a way of producing structure at the micrometer scale. Diode lasers are much cheaper, meaning that the technique is accessible to a broader audience, not just those in well-funded laboratories. In addition, the work highlights the competitiveness of femtosecond optical pulse generation using diode lasers compared to fibre lasers – the current most compact femtosecond laser systems. With some additional tweaking, the technique could be used in the field of nanorobotics, where robots on the micro and sub-micro scale have the potential to be used in vivo. There are also obvious applications for producing ever smaller and more intricate circuitry components. Moreover, photonic integration concepts will further promote this development and promise to deliver ever more compact and cost-effective femtosecond diode laser systems in the coming decade.

Factors Affecting Detection Power of Blood Oxygen-Level Dependent Signal in Resting-State Functional Magnetic Resonance Imaging Using High-Resolution Echo-Planar Imaging.

Latest developments in magnetic resonance imaging (MRI) hardware and software have significantly improved image acquisition for functional MRI (fMRI) techniques, including resting-state fMRI (rsfMRI). Specifically, with improvements in gradient and radiofrequency coils and advances in pulse sequence designs, functional images with higher spatiotemporal resolution can be achieved. However, while smaller voxel size has the benefit of resolving finer brain structures, it also decreases voxel-wise signal-to-noise ratio (SNR) and, subsequently, temporal SNR (tSNR), which is critical for the sensitivity of fMRI. Although the improved temporal resolution allows more image frames to be collected per unit time, the ability to detect brain activity by using the high spatiotemporal fMRI has not been fully characterized. Here, we aimed to evaluate the effects of spatial smoothing, scan length, sample size, seed size, and location on resting-state functional connectivity (rsFC) and tSNR by using data from the human connectome project. Results from this analysis show an important effect of smoothing on the rsFC strength (correlation values between the seed and the target) as well as on the tSNR. In contrast, while rsFC strength is not affected by sample size, the standard error decreases with the increasing number of participants, therefore improving the detection power for larger samples. Scan length and seed size seem to have a moderate effect on rsFC strength. Finally, seed location has an important impact on rsFC maps, as rsFC strength from cortical seeds seems higher than from sub-cortical seeds. In summary, our findings show that the choice of parameters can be critical for an rsfMRI study.

Cortical grey matter sodium accumulation is associated with disability and secondary progressive disease course in relapse-onset multiple sclerosis

ObjectiveSodium (23Na)-MRI is an emerging imaging technique to investigate in vivo changes in tissue viability, reflecting neuroaxonal integrity and metabolism. Using an optimised 23Na-MRI protocol with smaller voxel sizes and...

Halve the dose while maintaining image quality in paediatric Cone Beam CT

Cone beam CT (CBCT) for dentomaxillofacial paediatric assessment has been widely used despite the uncertainties of the risks of the low-dose radiation exposures. The aim of this work was to investigate the clinical performance of different CBCT acquisition protocols towards the optimization of paediatric exposures. Custom-made anthropomorphic phantoms were scanned using a CBCT unit in six protocols. CT slices were blinded, randomized and presented to three observers, who scored the image quality using a 4-point scale along with their level of confidence. Sharpness level was also measured using a test object containing an air/PMMA e,dge. The effective dose was calculated by means of a customized Monte Carlo (MC) framework using previously validated paediatric voxels models. The results have shown that the protocols set with smaller voxel size (180 µm), even when decreasing exposure parameters (kVp and mAs), showed high image quality scores and increased sharpness. The MC analysis showed a gradual decrease in effective dose when exposures parameters were reduced, with an emphasis on an average reduction of 45% for the protocol that combined 70 kVp, 16 mAs and 180 µm voxel size. In contrast, both “ultra-low dose” protocols that combined a larger voxel size (400 µm) with lower mAs (7.4 mAs) demonstrated the lowest scores with high levels of confidence unsuitable for an anatomical approach. In conclusion, a significant decrease in the effective dose can be achieved while maintaining the image quality required for paediatric CBCT.

Intracortical smoothing of small-voxel fMRI data can provide increased detection power without spatial resolution losses compared to conventional large-voxel fMRI data

Continued improvement in MRI acquisition technology has made functional MRI (fMRI) with small isotropic voxel sizes down to 1 mm and below more commonly available. Although many conventional fMRI studies seek to investigate regional patterns of cortical activation for which conventional voxel sizes of 3 mm and larger provide sufficient spatial resolution, smaller voxels can help avoid contamination from adjacent white matter (WM) and cerebrospinal fluid (CSF), and thereby increase the specificity of fMRI to signal changes within the gray matter. Unfortunately, temporal signal-to-noise ratio (tSNR), a metric of fMRI sensitivity, is reduced in high-resolution acquisitions, which offsets the benefits of small voxels. Here we introduce a framework that combines small, isotropic fMRI voxels acquired at 7 T field strength with a novel anatomically-informed, surface mesh-navigated spatial smoothing that can provide both higher detection power and higher resolution than conventional voxel sizes. Our smoothing approach uses a family of intracortical surface meshes and allows for kernels of various shapes and sizes, including curved 3D kernels that adapt to and track the cortical folding pattern. Our goal is to restrict smoothing to the cortical gray matter ribbon and avoid noise contamination from CSF and signal dilution from WM via partial volume effects. We found that the intracortical kernel that maximizes tSNR does not maximize percent signal change (ΔS/S), and therefore the kernel configuration that optimizes detection power cannot be determined from tSNR considerations alone. However, several kernel configurations provided a favorable balance between boosting tSNR and ΔS/S, and allowed a 1.1-mm isotropic fMRI acquisition to have higher performance after smoothing (in terms of both detection power and spatial resolution) compared to an unsmoothed 3.0-mm isotropic fMRI acquisition. Overall, the results of this study support the strategy of acquiring voxels smaller than the cortical thickness, even for studies not requiring high spatial resolution, and smoothing them down within the cortical ribbon with a kernel of an appropriate shape to achieve the best performance—thus decoupling the choice of fMRI voxel size from the spatial resolution requirements of the particular study. The improvement of this new intracortical smoothing approach over conventional surface-based smoothing is expected to be modest for conventional resolutions, however the improvement is expected to increase with higher resolutions. This framework can also be applied to anatomically-informed intracortical smoothing of higher-resolution data (e.g. along columns and layers) in studies with prior information about the spatial structure of activation.

Artifact reduction techniques in Cone Beam Computed Tomography (CBCT) imaging modality

Introduction: Cone beam computed tomography (CBCT) was introduced and became more common based on its low cost, fast image procedure rate and low radiation dose compared to CT. This imaging modality improved diagnostic and treatment-planning procedures by providing three-dimensional information with greatly reduced level of radiation dose compared to 2D dental imaging modalities for investigation of maxillofacial skeleton, dentition and the relationship of anatomical structures. However, CBCT is associated with multiple artifacts like. Extinction artifacts, beam hardening artifacts, partial volume effect, aliasing artifacts, ring artifacts and motion artifacts (misalignment artifacts), Noise and scatter. All of them leads to image quality reduction and have capability of Mistakenly considering as a pathological lesion. This study aimed to investigate Cone Beam Computed Tomography artifacts and their reduction procedures. Materials and Methods: A systematic search of the literature published from 2000 to 2017 in the PubMed, scopus and web of science databases was performed. The following key words combined in different ways: cone beam computed tomography, CBCT Artifacts and artifact reduction. Results: Artifact is caused by several factors containing reconstruction parameters like small field of views (FOVs), presence of metal objects, patient movement, etc. Artifact reduction methods can have divided into two categorize preprocessing in the projection domain and post processing in the image domain. Limitation of field of view, modification of patient head position or separating dental arches for scatter reduction, Application of high KVP in order to beam hardening reduction, iterative method and projection modification method for metal artifacts are recommended. In addition, Filtration, interpolation, iterative reconstruction and filtering algorithms, application of the smaller voxel size and respiratory gating are other suggested items for artifact reduction in CBCT. Conclusion: Multiple artifacts accompany CBCT imaging procedures. There for With the aim of improving the quality of the CBCT images; reducing the artifact caused scatter photons , various software-based and hardware-based correction methods are recommended .

Evaluation of maxillary trabecular microstructure as an indicator of implant stability by using 2 cone beam computed tomography systems and micro-computed tomography

The aim of this study was to assess the trabecular microarchitecture of the maxilla by using cone beam computed tomography (CBCT) and micro-computed tomography (micro-CT) ex vivo. Seventeen maxillary cadaver specimens were scanned by using micro-CT and CBCT devices. Samples were scanned with 2 CBCT devices at different voxel sizes (0.08, 0.125, and 0.160 mm for 3-D Accuitomo 170; 0.75 and 0.200 mm for Planmeca Promax 3-D Max). Morphometric parameters, such as bone volume/total volume (BV/TV) ratio, trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), trabecular number (Tb.N), and degree of anisotropy (DA) were assessed by using CTAnalyzer software. Bland-Altman limits of agreement and intraclass correlation coefficient (ICC) were performed to evaluate agreement between CBCT and micro-CT in consideration of measured morphometric parameters. Statistical significance was set at P < .05. The BV/TV, Tb.Th, Tb.Sp, and DA values were higher for CBCT images compared with micro-CT images, whereas the Tb.N value was lower with CBCT images than with micro-CT images. The BV/TV and DA parameters showed the highest agreement between CBCT and micro-CT devices (ICC = 0.421 for BV/TV and ICC = 0.439 for DA; P < .01). The BV/TV and DA parameters measured on CBCT obtained at the smallest voxel size were found to be useful for the assessment of maxillary trabecular microstructure.

Optimized Feature Extraction for Radiomics Analysis of 18F-FDG PET Imaging.

Radiomics analysis of 18F-FDG PET/CT images promises well for an improved in vivo disease characterization. To date, several studies have reported significant variations in textural features due to differences in patient preparation, imaging protocols, lesion delineation, and feature extraction. Our objective was to study variations in features before a radiomics analysis of 18F-FDG PET data and to identify those feature extraction and imaging protocol parameters that minimize radiomic feature variations across PET imaging systems. Methods: A whole-body National Electrical Manufacturers Association image-quality phantom was imaged with 13 PET/CT systems at 12 different sites following local protocols. We selected 37 radiomic features related to the 4 largest spheres (17-37 mm) in the phantom. On the basis of a combined analysis of voxel size, bin size, and lesion volume changes, feature and imaging system ranks were established. A 1-way ANOVA was performed over voxel size, bin size, and lesion volume subgroups to identify the dependency and the trend change in feature variations across these parameters. Results: Feature ranking revealed that the gray-level cooccurrence matrix and shape features are the least sensitive to PET imaging system variations. Imaging system ranking illustrated that the use of point-spread function, small voxel sizes, and narrow gaussian postfiltering helped minimize feature variations. ANOVA subgroup analysis indicated that variations in each of the 37 features and for a given voxel size and bin size can be minimized. Conclusion: Our results provide guidance to selecting optimized features from 18F-FDG PET/CT studies. We were able to demonstrate that feature variations can be minimized for selected image parameters and imaging systems. These results can help imaging specialists and feature engineers in increasing the quality of future radiomics studies involving PET/CT.

Automated Estimation of Standing Dead Tree Volume Using Voxelized Terrestrial Lidar Data

Standing dead trees (SDTs) are an important forest component and impact a variety of ecosystem processes, yet the carbon pool dynamics of SDTs are poorly constrained in terrestrial carbon cycling models. The ability to model wood decay and carbon cycling in relation to detectable changes in tree structure and volume over time would greatly improve such models. The specific objectives of this paper were to: 1) develop an automated SDT volume estimation algorithm providing accurate volume estimates for trees scanned with terrestrial lidar in dense forests; 2) assess the volume estimation algorithm’s accuracy with respect to large and small branches; and 3) characterize the impact of occlusion with regards to volume estimation accuracy and the ability of the algorithm to mitigate challenges posed by lower quality point clouds. A voxel-based volume estimation algorithm, “TreeVolX,” was developed and incorporates several methods designed to robustly process point clouds of varying quality levels. The algorithm operates on horizontal voxel slices by segmenting the slice into distinct branch or stem sections then applying an adaptive contour interpolation and interior filling process to create solid reconstructed tree models. The concept of vertical point cloud resampling is introduced to facilitate the modeling of lower quality point clouds with a small voxel size. TreeVolX estimated large and small branch volume with a root-mean-square error of 7.3% and 13.8%, respectively, and the adaptive contour interpolation was shown to significantly reduce volume estimation errors in the case of significantly occluded point clouds.

Impact of voxel size and scan time on the accuracy of three-dimensional radiological imaging data from cone-beam computed tomography

PurposeThree-dimensional (3D) radiological imaging plays an important role in surgical planning used in modern dentistry. The aim of this study was to optimize imaging parameters with a special focus on voxel size and scan time. Material and methodsA virtual 3D master model of a macerated human skull was generated using an industrial optical noncontact white light scanner. The skull was X-rayed with cone-beam computed tomography that was applied using different settings for voxel size and acquisition time (voxel edge length of 0.3 mm, scan times 4.8 s and 8.9 s; voxel edge length of 0.2 mm, scan times 14.7 s and 26.9 s). The scan was repeated 10 times at each setting. The CBCT scans were converted into 3D virtual models (actual value), which were superimposed with the 3D master model (reference value) to detect absolute differences. ResultsThe mean value of deviation increased with increasing voxel size and decreasing scan time. For a voxel edge length of 0.3 mm, the mean values of deviation were 0.33 mm and 0.22 mm with scan times of 4.8 s and 8.9 s, respectively. For a voxel edge length of 0.2 mm, the mean deviations were 0.16 mm and 0.14 mm with scan times of 14.7 s and 26.9 s, respectively. ConclusionsWhen using small voxel sizes, the scan time does not have a significant impact on image accuracy and therefore the scan time can be shortened. However, for larger voxel sizes, shorter scan times can lead to increased inaccuracy.

In-vitro validation of 4D flow MRI measurements with an experimental pulsatile flow model.

The purpose of this study was to assess the precision of four-dimensional (4D) phase-contrast magnetic resonance imaging (PCMRI) to measure mean flow and peak velocity (Vmax) in a pulsatile flow phantom and to test its sensitivity to spatial resolution and Venc. The pulsatile flow phantom consisted of a straight tube connected to the systemic circulation of an experimental mock circulatory system. Four-dimensional-PCMR images were acquired using different spatial resolutions (minimum pixel size: 1.5×1.5×1.5mm3) and velocity encoding sensitivities (up to three times Vmax). Mean flow and Vmax calculated from 4D-PCMRI were compared respectively to the reference phantom flow parameters and to Vmax obtained from two-dimensional (2D)-PCMRI. 4D-PCI measured mean flow with a precision of -0.04% to+5.46%, but slightly underestimated Vmax when compared to 2D-PCMRI (differences ranging from -1.71% to -3.85%). 4D PCMRI mean flow measurement was influenced by spatial resolution (P<0.001) with better results obtained with smaller voxel size. There was no effect of Venc on mean flow measurement. Regarding Vmax, neither spatial resolution nor Venc did influence the precision of the measurement. Using an experimental pulsatile flow model 4D-PCMRI is accurate to measure mean flow and Vmax with better results obtained with higher spatial resolution. We also show that Venc up to 3 times higher than Vmax may be used with no effect on these measurements.

Performance of Cone Beam Computed Tomography Systems in Visualizing the Cortical Plate in 3D Image Reconstruction: An In Vitro Study.

Introduction:Cortical bone is an important anatomical structure and its thickness needs to be determined prior to many dental procedures to ensure treatment success. Imaging modalities are necessarily used in dentistry for treatment planning and dental procedures. Three-dimensional image reconstruction not only provides visual information but also enables accurate measurement of anatomical structures; thus, it is necessarily required for maxillofacial examination and in case of skeletal problems in this region.Aims:This study aimed to assess the ability of three Cone Beam Computed Tomography (CBCT) systems including Cranex 3D, NewTom 3G and 3D Promax for Three-Dimensional (3D) image reconstruction of the cortical plate with variable thicknesses.Methods:Depending on the cortical bone thickness, samples were evaluated in three groups of ≤ 0. 5 mm, 0.6 -1 mm and 1.1-1.5 mm cortical bone thickness. The CBCT scans were obtained from each sample using three systems, their respective FOVs, and 3D scans were reconstructed using their software programs. Two observers viewed the images twice with a two-week interval. The ability of each system in the 3D reconstruction of different thicknesses of cortical bone was determined based on its visualization on the scans. The data were analyzed using SPSS and Kappa test.Results:The three systems showed the greatest difference in the 3D reconstruction of cortical bone with < 0.5 mm thickness. Cranex 3D with 4×6 cm2 FOV had the highest and 3D Promax with 8×8 cm2 FOV had the lowest efficacy for 3D reconstruction of cortical bone. Cranex 3D with 4×6 cm2 and 6×8 cm2 FOVs and NewTom 3G with 5×5 cm2 and 8×5 cm2 FOVs showed significantly higher efficacy for 3D reconstruction of cortical bone with 0.6-1mm thickness while 3D Promax followed by NewTom 3G with 8×8 cm2 FOV had the lowest efficacy for this purpose.Conclusion:Most CBCT systems have high efficacy for 3D image reconstruction of cortical bone with thicknesses over 1 mm while they have poor efficacy for image reconstruction of cortical bone with less than 0.5 mm thickness. Thus, for accurate visualization of anatomical structures on CBCT scans, systems with smaller FOVs and consequently smaller voxel size are preferred.

OA158] Noise equivalent number of quanta (NEQ): A tool for choosing the optimal reconstruction algorithm in computed tomography (CT)

Purpose Evaluate optimal reconstruction algorithm and voxel size for a breast CT system using NEQ. Methods CT scans of a wire phantom and a homogeneous cylindrical sample have been performed using a tomographic acquisition system for breast-CT with synchrotron radiation. By setting a monochromatic beam of 38 KeV , the images have been acquired using a CdTe photon-counting detector with a pixel size of 60 μ m. The optimal CT reconstruction algorithm has been investigated comparing the Filtered Back Projection (FBP), the Simultaneous Algebraic Reconstruction Technique (SART) and the Simultaneous Iterative Reconstruction Technique (SIRT). CT images have been reconstructed using two voxel sizes ( V 60 = 60 3 μ m3 and V 120 = 120 3 μ m3). The spatial resolution and the noise have been evaluated on CT reconstructions respectively trough the modulation transfer function (MTF) and the normalized noise power spectrum (NNPS). MTF has been evaluated with the thin wire method and the NNPS has been measured on the CT reconstructions of the homogeneous sample. The NEQ is defined as the ratio between the squared MTF and the NNPS. It is a measure of the signal to noise ratio in frequency domain and has been used to compare the performances of the considered reconstruction algorithms. Results For both used voxel sizes, compared to SART and FBP algorithms, SIRT algorithm shows highest values of NEQ for all accessible frequencies. Apart from the reconstruction algorithm, compared to V 60 , V 120 lead to better NEQ values for frequencies below 3.3 mm - 1 thus, for this system, details with diameter lower than 300 μ m are better resolved by the smallest voxel size available. Conclusions Summarizing information about spatial resolution and noise, NEQ is an extremely comprehensive metric which contains all the key issues for the global image quality assessment. For a given CT system, the comparison between NEQ curves measured on CT reconstructions provides a general method for choosing the best reconstruction algorithm and the voxel size to be used for achieving optimal performances in terms of spatial resolution and noise.

Diagnostic ability of limited volume cone beam computed tomography with small voxel size in identifying the superior and inferior walls of the mandibular canal

BackgroundThe aim of this study was to evaluate the visibility of the superior and inferior walls of the mandibular canal separately using limited volume cone beam computed tomography (CBCT) with small voxel size.MethodsCBCT cross-sectional images of 86 patients obtained by 3D Accuitomo FPD and reconstructed with a voxel size of 0.08 mm were used for the evaluation. A 30-mm range of the mandible just distal to the mental foramen was divided into three equal areas (areas 1, 2, and 3, from anterior to posterior). Each area contained 10 cross-sectional images. Two observers evaluated the visibility of the superior and inferior walls of the mandibular canal on each of the cross-sectional images in these three areas. The visibility ratio in each area was determined as the number of cross-sectional images with a visible wall divided by 10.ResultsIn all areas, the visibility ratio of the superior wall was significantly lower than that of the inferior wall. As for variance among the three areas, the ratio was highest in the most posterior area (area 3) and tended to decrease gradually towards the mental foramen for both walls. Cases in which more than two thirds of the superior wall could be identified (visibility ratio of 0.7 or more) in areas 1, 2, and 3 were 44, 62, and 66%, respectively.ConclusionsThe superior wall was significantly more poorly visualized than the inferior wall in all areas examined. The visibility of the superior wall on CBCT images was limited even when a limited volume device with small voxel size was used.

Can The Pore Scale Geometry Explain Soil Sample Scale Hydrodynamic Properties?

For decades, the development of new visualization techniques has brought incredible insights into our understanding of how soil structure affects soil function. X-ray microtomography is a technique often used by soil scientists but challenges remain with the implementation of the procedure, including how well the samples represent the uniqueness of the pore network and structure and the systemic compromise between sample size and resolution. We, therefore, chose to study soil samples from two perspectives: a macroscopic scale with hydrodynamic characterization and a microscopic scale with structural characterization through the use of X-ray microtomography (X-ray µCT) at a voxel size of 21.5³ µm³ (resampled at 43³ µm³). The objective of this paper is to unravel the relationships between macroscopic soil properties and microscopic soil structure. The twenty-four samples came from an agricultural field (Cutanic Luvisol) and the macroscopic hydrodynamic properties were determined using laboratory measurements of the saturated hydraulic conductivity (Ks), air permeability (ka), and retention curves (SWRC). The X-ray µCT images were segmented using a global method and multiple microscopic measurements were calculated. We used Bayesian statistics to report the credible correlation coefficients and linear regressions models between macro- and microscopic measurements. Due to the small voxel size, we observed unprecedented relationships, such as positive correlations between log(Ks) and a µCT global connectivity indicator, the fractal dimension of the µCT images or the µCT degree of anisotropy. The air permeability measured at a water matric potential of -70 kPa was correlated to the average coordination number and the X-ray µCT porosity, but was best explained by the average pore volume of the smallest pores. Continuous SWRC were better predicted near saturation when the pore-size distributions calculated on the X-ray µCT images were used as model input. We also showed a link between pores of different sizes. Identifying the key geometrical indicators that induce soil hydrodynamic behavior is of major interest for the generation of phenomenological pore network models. These models are useful to test physical equations of fluid transport that ultimately depend on a multitude of processes, and induce numerous biological processes.

CPU time optimization and precise adjustment of the Geant4 physics parameters for a VARIAN 2100 C/D gamma radiotherapy linear accelerator simulation using GAMOS

We have verified the GAMOS/Geant4 simulation model of a 6 MV VARIAN Clinac 2100 C/D linear accelerator by the procedure of adjusting the initial beam parameters to fit the percentage depth dose and cross-profile dose experimental data at different depths in a water phantom. Thanks to the use of a wide range of field sizes, from 2 × 2 cm2 to 40 × 40 cm2, a small phantom voxel size and high statistics, fine precision in the determination of the beam parameters has been achieved. This precision has allowed us to make a thorough study of the different physics models and parameters that Geant4 offers. The three Geant4 electromagnetic physics sets of models, i.e. Standard, Livermore and Penelope, have been compared to the experiment, testing the four different models of angular bremsstrahlung distributions as well as the three available multiple-scattering models, and optimizing the most relevant Geant4 electromagnetic physics parameters. Before the fitting, a comprehensive CPU time optimization has been done, using several of the Geant4 efficiency improvement techniques plus a few more developed in GAMOS.

Influence of voxel size on the accuracy of linear measurements of the condyle in images of cone beam computed tomography: A pilot study.

BackgroundTo analyze the influence of voxel size and exposure time on the accuracy of linear measurements of the condyle.Material and MethodsFour macerated hemi-mandibles of pigs were scanned in nine different voxel size protocols. Three-dimensional models of the condyle were generated in order to establish a comparison between linear measurements obtained with each voxel protocol and those obtained with a caliper (gold standard). The comparison between the protocols was performed considering the average of the two measurements of the condyle in the latero-medial (LM) and antero-posterior (AP) axes and also through repeated measurement ANOVA with rank transformation. The level of significance was 5%.ResultsA significant difference was found between the protocols regarding the LM and AP variables (p-values = 0.0027 and 0.0263, respectively). In the LM axis, the protocol P6 (voxel size of 0.3 mm with scan time of 4.8 seconds) did not show statistical difference compared to the gold standard. The protocols P4 and P5 (voxel size of 0.25 mm with scan times of 14.7 and 26.9 seconds, respectively) were both statistically similar compared to caliper, although they have presented a longer scan time. In the AP axis, the protocol P8 (voxel size of 0.4 mm with time scan of 4.8 seconds) was statistically similar to the gold standard.ConclusionsA smaller voxel size does not necessarily mean more accuracy regarding the linear measurements of the condyle. It is possible to obtain an acceptable level of accuracy with a larger voxel size and a shorter exposure time to radiation. Key words:CBCT, voxel size, linear measurement, diagnostic imaging.

Influence of voxel size on cone-beam computed tomography-based detection of vertical root fractures in the presence of intracanal metallic posts.

PurposeThis study was performed to evaluate the influence of voxel size and the accuracy of 2 cone-beam computed tomography (CBCT) systems in the detection of vertical root fracture (VRF) in the presence of intracanal metallic posts.Materials and MethodsThirty uniradicular extracted human teeth were selected and randomly divided into 2 groups (VRF group, n=15; and control group, n=15). The VRFs were induced by an Instron machine, and metallic posts were placed in both groups. The scans were acquired by CBCT with 4 different voxel sizes: 0.1 mm and 0.16 mm (for the Eagle 3D V-Beam system) and 0.125 mm and 0.2 mm (for the i-CAT system) (protocols 1, 2, 3, and 4, respectively). Interobserver and intraobserver agreement was assessed using the Cohen kappa test. Sensitivity and specificity were evaluated and receiver operating characteristic analysis was performed.ResultsThe intraobserver coefficients indicated good (0.71) to very good (0.83) agreement, and the interobserver coefficients indicated moderate (0.57) to very good (0.80) agreement. In respect to the relationship between sensitivity and specificity, a statistically significant difference was found between protocols 1 (positive predictive value: 0.710, negative predictive value: 0.724) and 3 (positive predictive value: 0.727, negative predictive value: 0.632) (P<.05). The least interference due to artifact formation was observed using protocol 2.ConclusionProtocols with a smaller voxel size and field of view seemed to favor the detection of VRF in teeth with intracanal metallic posts.

3D tomographic imaging with the γ-eye planar scintigraphic gamma camera

γ-eye is a desktop planar scintigraphic gamma camera (100 mm × 50 mm field of view) designed by BET Solutions as an affordable tool for dynamic, whole body, small-animal imaging. This investigation tests the viability of using γ-eye for the collection of tomographic data for 3D SPECT reconstruction. Two software packages, QSPECT and STIR (software for tomographic image reconstruction), have been compared. Reconstructions have been performed using QSPECT’s implementation of the OSEM algorithm and STIR’s OSMAPOSL (Ordered Subset Maximum A Posteriori One Step Late) and OSSPS (Ordered Subsets Separable Paraboloidal Surrogate) algorithms. Reconstructed images of phantom and mouse data have been assessed in terms of spatial resolution, sensitivity to varying activity levels and uniformity. The effect of varying the number of iterations, the voxel size (1.25 mm default voxel size reduced to 0.625 mm and 0.3125 mm), the point spread function correction and the weight of prior terms were explored. While QSPECT demonstrated faster reconstructions, STIR outperformed it in terms of resolution (as low as 1 mm versus 3 mm), particularly when smaller voxel sizes were used, and in terms of uniformity, particularly when prior terms were used. Little difference in terms of sensitivity was seen throughout.