Axial Dimensions Research Articles

Maximal Axial Vertebral Rotation in Adolescent Idiopathic Scoliosis: Is the Apical Vertebra the Most Rotated?

Study Design:Retrospective cross-sectional study.Objectives:It is generally believed that the apical vertebra has the largest axial rotation in adolescent idiopathic scoliosis. We investigated the relationship between apical axial vertebral rotation (apicalAVR) and maximal axial vertebral rotation (maxAVR) in both major and minor curves using biplanar stereo-imaging.Methods:EOS 2D/3D biplanar radiograph images were collected from 332 patients with adolescent idiopathic scoliosis (Cobb angle range 10°-122°, mean age 14.7 years). Based on the X-ray images, with the help of 3D full spine reconstructions Cobb angle, curvature level, apicalAVR and maxAVR were determined. These parameters were also determined for minor curves in Lenke 2, 3, 4, 6 type patients. Maximal thoracic rotation and maximal thoracolumbar/lumbar rotation were calculated. Statistical analysis was performed with descriptive statistics, Shapiro-Wilk test, and Wilcoxon signed-rank test.Results:The apical vertebrae were the most rotated vertebra in only 40.4% of the major curves, and 31.7% in minor curves. MaxAVR significantly exceeded apicalAVR values in the major curves (P < .001) as well as in minor curves (P < .001). The 2 parameters differed significantly in each severity group and Lenke type.Conclusions:The apical vertebrae were not the most rotated vertebra in more than half of cases investigated indicating that apicalAVR and maxAVR should be considered as 2 distinct parameters, of which maxAVR fully describes the axial dimension of scoliosis. Furthermore, the substitution of maxAVR for the apicalAVR should be especially avoided in double and triple curves, as the apical vertebra was even less commonly the most rotated in minor curves.

Eccentricity-dependent effects of simultaneous competing defocus on emmetropization in infant rhesus monkeys

Dual-focus lenses that impose simultaneous competing myopic defocus over the entire visual field produce axial hyperopic shifts in refractive error. The purpose of this study was to characterize the effects of eccentricity on the ability of myopic defocus signals to influence central refractive development in infant monkeys. From 24 to 152 days of age, rhesus monkeys were reared with binocular, dual-focus lenses that had central, zero-powered zones surrounded by alternating concentric annular power zones of +3D and zero power. Between subject groups the diameter of the central, zero-powered zone was varied from 2 mm to 8 mm in 2 mm steps (+3D/pl 2 mm, n = 6; +3D/pl 4 mm, n = 6; +3D/pl 6 mm, n = 8, or + 3D/pl 8 mm, n = 6). For the treatment lens with 2, 4, 6 and 8 mm central zones, objects at eccentricities beyond 11°, 16°, 19° and 23°, respectively, were imaged exclusively through the dual-power peripheral zones. Refractive status (retinoscopy), corneal power (keratometry) and axial dimensions (ultrasonography) were measured at two-week intervals. Comparison data were obtained from monkeys reared with binocular, single-vision +3D full-field lenses (+3D FF, n = 6) and 41 normal control monkeys reared with unrestricted vision. At the end of the rearing period, with the exception of the +3D/pl 8 mm group (median = +3.64 D), the ametropias for the other lens-reared groups (medians: FF = +4.39 D, 2 mm = +5.19 D, 4 mm = +5.59 D, 6 mm = +3.50 D) were significantly more hyperopic than that for the normal monkeys (+2.50 D). These hyperopic errors were associated with shallower vitreous chambers. The key finding was that the extent and consistency of these hyperopic ametropias varied with the eccentricity of the dual-focus zones. The results confirm that myopic defocus in the near periphery can slow axial growth, but that imposed defocus beyond about 20° from the fovea does not consistently alter central refractive development.

A role of color vision in emmetropization in C57BL/6J mice

Spectral composition affects emmetropization in both humans and animal models. Because color vision interacts the effects of chromatic defocus, we developed a method to bypass the effects of longitudinal chromatic aberration by placing a spectral filter behind the optics of the eye, using genetic tools. Newborn C57BL/6J (B6) mice were reared in quasi-monochromatic red (585–660 nm) or blue (410–510 nm) light beginning before eye-opening. Refractive states and ocular dimensions were compared at 4, 6, 8, and 10 weeks with mice reared in normal white light. Cre recombinase-dependent Ai9 reporter mice were crossed with Chx10-Cre to obtain Chx10-Cre;Ai9 mice, expressing red fluorescent protein in retinal Cre-positive cells. Ai9 offsprings, with and without Cre, were reared under a normal visual environment. Refraction and axial components were measured as described above. Expression levels of M and S opsin were quantified by western blotting at 10 weeks. Compared with those reared in white light, B6 mice reared in red light developed relative hyperopia, principally characterized by flattening of corneal curvature. Emmetropization was not affected by blue light, possibly because the reduction in vitreous chamber depth compensated for the increase in corneal curvature. Compared with Cre-negative littermates, the refraction and axial dimensions of Chx10-Cre;Ai9 mice were not significantly different at the follow-up timepoints. M opsin levels were higher in Chx10-Cre;Ai9 mice at 10 weeks while S opsin levels were not different. Red light induced a hyperopic shift in mouse refractive development. Emmetropization was not impacted in mice with perturbed color vision caused by intrinsic red-fluorescent protein, suggesting that color vision may not be necessary in mouse emmetropization when other mechanisms are present.

Relationship between Three-Dimensional Magnetic Resonance Imaging Eyeball Shape and Optic Nerve Head Morphology

To determine if the 3-dimensional (3D) eyeball shape is associated with the positions of the central retinal vascular trunk (CRVT) and the externally oblique border (EOB) in the optic nerve head (ONH). Prospective, cross-sectional study. Fifty-six subjects (112 eyes) with a diagnosis of glaucoma or glaucoma suspect. The eyeball shape on 3D magnetic resonance imaging (MRI) scans was classified according to the dimension of the longest diameter: axial dimension (prolate sphere), group 1; horizontal dimension (horizontally oblate sphere), group 2; and vertical dimension (vertically oblate sphere), group 3. The deviation of the CRVT, as a surrogate of lamina cribrosa (LC) shift, was measured from the center of the Bruch's membrane opening (BMO) demarcated by OCT imaging, with the horizontal midline as 0° and the superior location as a positive value. The angular location of the longest EOB was also measured. Positions of CRVT and EOB according to the 3D eyeball shape. Among 112 eyes, 54 (48%) had a prolate shape (group 1), 23 (21%) had a horizontally oblate shape (group 2), and 35 (31%) had a vertically oblate shape (group 3). The angular deviation of the CRVT differed among the groups: to the nasal side in group 1, to the temporal side in group 2, and along the vertical meridian in group 3. In cases of asymmetric eyeball shape, the CRVT was deviated toward the undergrown side from the overgrown side, regardless of grouping. The angular location of the longest EOB was in the direction opposite to the CRVT position (P < 0.001). A generalized estimating equation analysis revealed that the temporal location of the CRVT was associated with older age (P= 0.001), nasal location of the longest EOB (P < 0.001), and oblate shape of the eyeball (P < 0.001, group 2; P= 0.007, group 3). The position of the CRVT and EOB were associated with the 3D eyeball shape. Considering that infant ONH morphology is highly uniform, various modes of eyeball expansion during growth can result in diverse directionalities of offset between the LC and the BMO in adults.

Long-term Surveillance of Patients with Complete Response Following Chemotherapy for Metastatic Nonseminomatous Germ Cell Tumor

BackgroundThere is controversy regarding the management of patients with normal markers and residual masses (≤1 cm) after chemotherapy for nonseminomatous germ cell tumors (NSGCTs). ObjectiveTo determine long-term outcomes of a surveillance strategy in such patients. Design, setting, and participantsA retrospective review of our multidisciplinary testicular cancer database was performed. All patients who underwent primary chemotherapy for metastatic NSGCTs were identified between 1981 and 2016. A complete response (CR) was defined as normalization of serum tumor markers and a ≤1 cm residual mass in the largest axial dimension following chemotherapy. All such patients were surveilled. Outcome measurements and statistical analysisOutcome variables of interest were time to death, time to cancer-specific survival, and time to relapse. Overall survival and relapse-free survival were calculated using the Kaplan-Meier method, and the cumulative incidence of cause-specific survival rates was calculated using competing risk analysis. The impact of risk group and chemotherapy regimen on relapse-free survival was assessed using log-rank test. Results and limitationsDuring the study period, 1429 metastatic germ cell tumor patients were treated with primary chemotherapy. CR was achieved in 191 (18.5%) NSGCT patients. The median age at diagnosis was 27.4 yr, with a median follow-up of 81.1 mo. The majority had American Joint Committee on Cancer stage II at diagnosis (I: 23.8%; II: 49.2%; III: 27%) and International Germ Cell Cancer Collaborative Group good-risk disease (good: 78%; intermediate: 17.8%; poor: 4.2%). Of the 191 patients with a CR, 175 (91.6%) never relapsed and remain disease free. Sixteen (8.4%) patients relapsed after a median of 11.3 mo (range 1–332 mo), with over half (nine patients; 4.7%) relapsing in the retroperitoneum only and salvaged successfully with postchemotherapy retroperitoneal lymph node dissection (PC-RPLND) alone. Of these nine patients, only two (1%) had viable disease in the PC-RPLND specimen. The remaining seven patients had relapses outside the retroperitoneum and received salvage chemotherapy ± postchemotherapy resection. Overall, nine (4.7%) patients have died, but only four (2.1%) from testis cancer. ConclusionsOur data, the largest series to date, confirm that surveillance is safe and effective for men who achieve a CR following chemotherapy for metastatic NSGCTs. Patient summarySurveillance is a safe strategy for patients who achieve a complete response following chemotherapy for metastatic testis cancer.

Effects of low intensity ambient lighting on refractive development in infant rhesus monkeys (Macaca mulatta)

Studies in chickens suggest low intensity ambient lighting causes myopia. The purpose of this experiment was to examine the effects of low intensity ambient lighting (dim light) on normal refractive development in macaque monkeys. Seven infant rhesus monkeys were reared under dim light (room illumination level: ~55 lx) from 24 to ~310 days of age with otherwise unrestricted vision. Refractive error, corneal power, ocular axial dimensions, and choroidal thickness were measured in anesthetized animals at the onset of the experiment and periodically throughout the dim-light-rearing period, and were compared with those of normal-light-reared monkeys. We found that dim light did not produce myopia; instead, dim-light monkeys were hyperopic relative to normal-light monkeys (median refractive errors at ~155 days, OD: +3.13 D vs. +2.31 D; OS: +3.31D vs. +2.44 D; at ~310 days, OD: +2.75D vs. +1.78D, OS: +3.00D vs. +1.75D). In addition, dim-light rearing caused sustained thickening in the choroid, but it did not alter corneal power development, nor did it change the axial nature of the refractive errors. These results showed that, for rhesus monkeys and possibly other primates, low ambient lighting by itself is not necessarily myopiagenic, but might compromise the efficiency of emmetropization.

Determination of selected physical properties of three varieties of shelled and unshelled melon seeds

The physical properties of shelled and unshelled melon seeds for three different varieties: C. cucurbita, C. vulgaris and C. lanatus were investigated at the moisture contents of 5.3, 5.1 and 6.0% dry basis respectively. The axial dimension, mean diameter, sphericity, surface area, porosity, true and bulk density, angle of repose, coefficient of friction of the three varieties of melon seeds were determined using standard methods. The results obtained from the study revealed that length, width, thickness, arithmetic and geometric diameter, sphericity, surface area and 1000 unit mass ranged from 12.81-14.50 mm, 7.02-8.42 mm, 2.22-2.49 mm, 7.36-8.31 mm, 5.84- 6.54 mm, 0.47- 0.53, 134.64-192.23 mm² and 94.0- 110.0g respectively. Sphericity was 0.41, 0.41 and 0.36 for shelled C. lanatus, cucurbita and c. vulgaris, while the values for unshelled varieties are 0.43, 0.42 and 0.41 respectively. Surface area was 116 mm2,139 mm2 and 180 mm2 for shelled C. lanatus, cucurbita and C. vulgaris ,while the values for unshelled varieties are 186 mm2,205 mm2 and 283 mm2.One thousand unit mass was 89.6g,82.2g and 95.8g for shelled C. lanatus, cucurbita and C. vulgaris ,while the values for unshelled varieties are 98g,94g,and 110g respectively. Angle of repose was 26.3o, 25.4 o and 26.1 o for shelled C. lanatus, cucurbita and C. vulgaris, while the values for unshelled varieties are 23.6o, 20o and 23.5o respectively. Bulk density was 458 g/mm3, 389 g/mm3 and 423 g/mm3 for shelled C. lanatus, cucurbita and C. vulgaris, while the values for unshelled varieties are 543 g/mm3, 405 g/mm3, and 446 g/mm3 respectively. Finally porosities of 34.8%, 47.9% and 48.5% were obtained for shelled C. lanatus, cucurbita and C. vulgaris, while the values for unshelled varieties are 37.3%, 53.7% and 48.5% respectively.

Optical Incoherence Tomography: a method to generate tomographic retinal cross-sections with non-interferometric adaptive optics ophthalmoscopes.

We present Optical Incoherence Tomography (OIT): a completely digital method to generate tomographic retinal cross-sections from en-face through-focus image stacks acquired by non-interferometric imaging systems, such as en-face adaptive optics (AO)-ophthalmoscopes. We demonstrate that OIT can be applied to different imaging modalities using back-scattered light, including systems without inherent optical sectioning and, for the first time, multiply-scattered light, revealing a distinctive cross-sectional view of the retina. The axial dimension of OIT cross-sections is given in terms of focus position rather than optical path, as in OCT. We explore this property to guide focus position in cases where the user is "blind" focusing, allowing precise plane selection for en-face imaging of retinal pigment epithelium, the vascular plexuses and translucent retinal neurons, such as photoreceptor inner segments and retinal ganglion cells, using respectively autofluorescence, motion contrast and split detection techniques.

Test Analysis and Simulation Calculation of Temperature Field for Dry-Type Air-Core Reactor

Based on test analysis and simulation calculation of temperature field for dry-type air-core reactor, the temperature rise rule of internal axial dimension and enveloping internal conductor were analyzed. The highest temperature rise point in the envelope is located about 1/4 of the packet seal. The temperature rise difference between the inner wires is small, and the temperature rise difference within the envelope is less than 1 °C. The radial distribution of temperature along the insulating impregnated glass fiber has a great gradient. The temperature in the middle of the airway is near room temperature, and the temperature rise is about 5K, and the internal temperature of the airway has a larger gradient. For airway width design, the influence of the change of the airway width of the temperature rise distribution should be considered.

Enhanced 4Pi single-molecule localization microscopy with coherent pupil based localization

Over the last decades, super-resolution techniques have revolutionized the field of fluorescence microscopy. Among them, interferometric or 4Pi microscopy methods exhibit supreme resolving power in the axial dimension. Combined with single-molecule detection/localization and adaptive optics, current 4Pi microscopy methods enabled 10–15 nm isotropic 3D resolution throughout whole cells. However, further improving the achieved 3D resolution poses challenges arising from the complexity of single-molecule emission patterns generated by these coherent single-molecule imaging systems. These complex emission patterns render a large portion of information carrying photons unusable. Here, we introduce a localization algorithm that achieves the theoretical precision limit for a 4Pi based single-molecule switching nanoscopy (4Pi-SMSN) system, and demonstrate improvements in localization precision, accuracy as well as stability comparing with state-of-the-art 4Pi-SMSN methods.

Axial Domain Wall Dimension in Bistable Glass-Coated Microwire

Axial Domain Wall Dimension in Bistable Glass-Coated Microwire

Optically Resolved Fuel Regression of a Clear Polymethylmethacrylate Hybrid Rocket Motor

A novel fuel regression measurement technique was developed using a single-port, clear polymethylmethacrylate (PMMA) grain and a high-resolution camera, providing temporally and spatially resolved data in a small-scale hybrid motor. By visualizing the fully illuminated port through a flat PMMA surface, the fuel grain diameter can be measured along the axial dimension. This paper provides the details of the implementation, data processing, validation, and results from 21 hotfires. A wide range of operating conditions were tested by varying the initial diameter, the fuel grain length, the oxidizer mass flow rate, and the precombustion chamber length. The main difficulty associated with this technique is correcting the data to account for the change in index of refraction of the solid PMMA as heat soaks into the material surrounding the port. Qualitative and quantitative data can be extracted to further improve our fundamental understanding of hybrid combustion and upgrade motor designs. This new regression method is nonintrusive, low cost, and easy to implement, and it has the potential to provide reliable space–time-dependent data for laboratory-scale motors.

Characterization of the Shape Anisotropy of Superparamagnetic Iron Oxide Nanoparticles during Thermal Decomposition.

Magnetosomes are near-perfect intracellular magnetite nanocrystals found in magnetotactic bacteria. Their synthetic imitation, known as superparamagnetic iron oxide nanoparticles (SPIONs), have found applications in a variety of (nano)medicinal fields such as magnetic resonance imaging contrast agents, multimodal imaging and drug carriers. In order to perform these functions in medicine, shape and size control of the SPIONs is vital. We sampled SPIONs at ten-minutes intervals during the high-temperature thermal decomposition reaction. Their shape (sphericity and anisotropy) and geometric description (volume and surface area) were retrieved using three-dimensional imaging techniques, which allowed to reconstruct each particle in three dimensions, followed by stereological quantification methods. The results, supported by small angle X-ray scattering characterization, reveal that SPIONs initially have a spherical shape, then grow increasingly asymmetric and irregular. A high heterogeneity in volume at the initial stages makes place for lower particle volume dispersity at later stages. The SPIONs settled into a preferred orientation on the support used for transmission electron microscopy imaging, which hides the extent of their anisotropic nature in the axial dimension, there by biasing the interpretation of standard 2D micrographs. This information could be feedback into the design of the chemical processes and the characterization strategies to improve the current applications of SPIONs in nanomedicine.

Rapid functional optoacoustic micro-angiography in a burst mode.

Optoacoustic microscopy (OAM) can image intrinsic optical absorption contrast at depths of several millimeters where state-of-the-art optical microscopy techniques fail due to intense light scattering in living tissues. Yet, wide adoption of OAM in biology and medicine is hindered by slow image acquisition speed, small field of view (FOV), and/or lack of spectral differentiation capacity of common system implementations. We report on a rapid acquisition functional optoacoustic micro-angiography approach that employs a burst-mode laser triggering scheme to simultaneously acquire multi-wavelength 3D images over an extended FOV covering ${50}\;{\rm mm} \times {50}\;{\rm mm}$50mm×50mm in a single mechanical overfly scan, attaining 28 µm and 14 µm resolution in lateral and axial dimensions, respectively. Owing to an ultrawideband low-noise design featuring a spherically focused polyvinylidene difluoride transducer, we demonstrate imaging of human skin and underlying vasculature at up to 3.8 mm depth when using per-pulse laser energies of only 25 µJ without employing signal averaging. Overall, the developed system greatly enhances performance and usability of OAM for dermatologic and micro-angiographic studies.

Afocal Mirror Systems with Small Axial Dimensions

The searching and designing new solutions for mirror systems, including afocal ones, has been studied for decades. In the design, it has always been difficult to combine optimization and cost. Nowadays, the problem remains relevant. The widespread use of mirror systems is due to some aspects: thermal stability, high resolution in a wide spectral range, and the absence of image defects due to chromatic aberrations. All this provides superior performance compared to lens systems. The purpose of this paper is the design of two compact afocal mirror systems with small axial dimensions. Schemes of afocal three mirror systems with small axial dimensions are presented. The schemes can also be called compacts. A study was made of systems in which the diameter of the aperture diaphragm in the primary mirror is modified, which leads to a more compact system. A calculation algorithm of new the systems is proposed, with correction of the image curvature. A summary of formulas of the main parameters of the system is given, and various design solutions are calculated for angular field of view 2ω = 20ˈ and diameter of the entrance pupil D = 35 and D = 70 mm. Computer simulations were performed in the Opal , Zemax , and Code V software. The designed systems have good correction of aberrations for the given characteristics: in the spot diagrams, the values of the RMS scatter spot do not exceed 1,35 μm; GEO radius (distance from the reference point) – 0.105 μm; together with Airy disk sizes of about 9.16 μm, indicating that the images are close to diffraction. The calculated systems can be successfully applied as part of a more complex system, as well as in systems with a synthesized aperture.

WEDM of AA6061: an insight investigation of axial and lateral dimensional errors

ABSTRACT Geometrical machining errors in terms of overcut and/or undercut are the inherent problems associated with wire-cut electric discharge machining (EDM) process. Such errors are ultimately transformed into compromised dimensional accuracy of the machined part. The magnitude of the said errors is presumed the same in both the cutting orientation of work part. However, practically there exists variations along both the cutting orientations, i.e. axial and lateral. Moreover, not only the lateral and axial dimensions are different from the designed dimensions but also a noticeable difference in errors magnitude is observed along both the cutting directions. Variation in kerf along different edges of the machined profile also plays a pivotal role in error amplification. Such difference in geometrical dimensions seriously matters in high-precision applications. Therefore, the present research examines the impact of seven control parameters for minimizing the magnitude of kerf width, axial and lateral dimensional errors. Al-alloy 6061 is taken as a substrate because of its wide use in precision-oriented applications. Parametric effects are thoroughly analyzed through statistical tests and SEM-based analysis. Results revealed that the use of optimal settings yields a reduction of 13.5%, 49%, and 27% in the magnitudes of kerf width, axial, and lateral dimensional errors, respectively.

3D light-field endoscopic imaging using a GRIN lens array

Endoscopic observation of biological tissues with quantitative depth perception, effective volumetric recognition of anatomical features, and efficient 3D navigation is critical for optical diagnostics and minimally invasive surgery for various target diseases. Light-field techniques have recently emerged as a promising approach to 3D photography and microscopy due to their scanning-free, highly scalable, and volumetric imaging capabilities. These advantages hold great potential for application to optical endoscopy, as the existing clinical endoscopy systems rely primarily on a 2D projection or use polarized glasses to provide visual parallax of complex 3D structures. Here, we report a light-field endoscopy prototype using a GRIN lens array (GLA). The GLA-based system maintains consistent spatial measurements with clinical endoscopic systems, a compact size in comparison with compound objective lenses, as well as the ability to maximally capture the angular information necessary for 3D imaging. We also present a computational strategy combining a wave-optics model and a hybrid point-spread function for high-resolution volumetric reconstruction. The system achieves spatial resolutions of 20–60 μm and 100–200 μm in the lateral and axial dimensions, respectively, across an imaging volume of ∼5 mm × 5 mm × 10 mm. We anticipate the prototype to offer a promising paradigm for glasses-free, high-resolution 3D medical endoscopy.

A dual-intake-port technology as a design option for a Sliding Vane Rotary Expander of small-scale ORC-based power units

Volumetric machines are the most suitable candidates to be used as expander in power units based on the Organic Rankine Cycle (ORC) thermodynamic concept, for waste heat recovery of Internal Combustion Engine in the on-the-road transportation sector. In particular, the technology of the Sliding Rotary Vane Expander (SRVE) shows intrinsic advantages thanks to their lower cost, shaping features, easier manufacturing and reliability and, generally speaking, very suitable operative conditions. Nevertheless, they show some disadvantages which are typical of volumetric machines, such as low capacity, limited expansion ratio and power lost by friction.Among the different technologies available to reduce the effects of these aspects (revolution speed increase, elliptical stators or with more complex geometries, tip blade optimization, rolling stators, etc.), the Dual-Intake Port (DIP) was assessed as a promising solution to enhance SVREs performance and operability. However, dual-intake port was still not conceived as design option.In this paper, a novel Sliding Vane Rotary Expander design concept involving a Dual Intake Port expander (DIP) option was developed and compared to the conventional Single Intake Port (SIP) one, under the same operating conditions. Thus, after an experimental comparison between SIP and DIP expanders, under the same conditions of mass flowrate, a theoretical expander model of the latter was validated on a set of experimental results. The model allows to outline the advantages of considering the dual port as a design option: for a specific flow rate and revolution speed, this option allows to reduce the friction losses, which represent a weak point of this volumetric machine. For a given mass flow rate of the working fluid, an additional feature is that it allows a sensible downsizing with respect to the SIP, with an axial dimension reduction up to 50%, ensuring additional weight and space saving. Despite the reduction of the dimensions, DIP produces a comparable mechanical power with respect to SIP, limiting the reduction to 8–10% of the SIP one with a 50% lower mechanical power loss due to friction. For the same flow rate, the added intake port determines a decrease of the intake pressure which is completely beneficial in terms of operating conditions of the overall recovery unit.

Type synthesis of 90°/180° dual-function upenders for large shell units of nuclear reactor

In this paper, unit vectors collinear with the axes of large shell units of nuclear reactors were used to represent the poses of the workpieces. Based on the motion operator interpretation of the rotation matrix, 60 kinds of rotation matrix permutations with 90° turns as the step length to achieve 180° flipping of the workpiece were obtained. After eliminating invalid permutations and merging homogenous permutations, class I, II, and III flipping motion models were obtained. By calculating the Lie algebra of each step of rigid body motion in the flipping motion model, the twist and the motion pair property for each step were obtained. By means of the permutation and combination theory, the sequence of the motion pairs for different configurations was determined, and the rules between sequential transformations and axis changes of the motion pairs under the initial configuration were stipulated. Three classes of 19 initial configurations of 90°/180° dual-function upenders were constructed. For three of them, taking into account the characteristics of the axial dimension variation of workpieces, prismatic pairs were added along the workpiece’s axis (vector), and 15 overall configurations of 90°/180° dual-function upenders were synthesized. This provides the basic theoretical support for the innovative design of upenders with independent intellectual property rights.

Physical performance of a long axial field-of-view PET scanner prototype with sparse rings configuration: A Monte Carlo simulation study.

There is a growing interest in extending the axial fields-of-view (AFOV) of PET scanners. One major limitation for the widespread clinical adoption of such systems is the multifold increase in the associated material costs. In this study, we propose a cost-effective solution to extend the PET AFOV using a sparse detector rings configuration. The corresponding physical performance was validated using Monte Carlo simulations. Monte Carlo model of the Siemens BiographTM mCT PET/CT, with a 21.8cm AFOV and a set of compact rings of LSO crystals was developed as a gold standard. The mCT configuration was then modified by interleaving the LSO crystals in the axial direction within each detector block with 4mm physical gaps (equivalent to the LSO crystal axial dimension) thus extending the AFOV to 43.6cm (Ex-mCT). The physical performances of the two MC models were assessed and then compared using NEMA NU 2-2007 standards. Ex-mCT showed <0.2mm difference in transaxial spatial resolution, and, 0.8mm and 0.3mm deterioration in axial spatial resolution, compared to the mCT, at 1 and 10cm off-center of the transaxial field-of-view respectively. The system sensitivities for the mCT and Ex-mCT models were 9.4±0.2 and 10.75±0.2cps/kBq respectively. The higher sensitivity of Ex-mCT was due to four additional detector rings required to double the mCT AFOV. PET images of the NEMA Image Quality (IQ) phantom showed no artifacts due to detector rings sparsity, and all spheres were visible in both configurations. Ex-mCT achieved percent contrast recoveries within 5.6% of those of the mCT for all spheres and a maximum of 36% higher background variability at the center of the AFOV. The Ex-mCT, however, showed a more uniform noise distribution over an axial range of almost twice the length of the mCT AFOV. Using the proposed sparse detector-ring configuration, the AFOV of current generation PET systems can be doubled while maintaining the original number and volume of detector crystal elements, and without jeopardizing the system's overall physical performance. Despite an increase in the noise level, the Ex-mCT exhibited an improved noise uniformity.