Cold Rod Research Articles

Development of a novel phantom for tau PET imaging

PurposeThe cortical uptake of tau positron emission tomography (PET) tracers corresponds to the Braak stage and reflects the distribution and progression of tau neurofibrillary tangles. The present study aimed to develop and validate the basic performance of a novel tau PET phantom, as well as to establish standard test procedures and analytical methods. MethodsThe tau PET phantom consisted of a brain simulation section simulated medial temporal lobe region and resolution and uniformity sections. The brain simulation section and hot rods and uniformity section contained 4 and 2 kBq/mL of 18F, respectively and images were acquired three times for 20 min with a PET/CT scanner. The resolution section was visually assessed with two sets of hot and cold rods. Recovery coefficients (RCs) as a quantitative value and coefficient of variation (CV) as image noise were determined based on the brain simulation and the uniformity section, respectively. ResultsPreparation of activity in the phantom was repeatable among three measurements. The quality of images in the brain simulation and uniformity section with the rods was good. The 5- or 6-mm rods were detected separately. The mean RCs calculated based on the VOI template were between 0.75 and 0.83. The CV at the center slice of uniformity section was 5.54%. ConclusionsWe developed a novel tau PET phantom to assess quantitative value, image noise, and detectability and resolution from brain simulation section, uniformity section, and rods, respectively. This phantom will contribute to the standardization and harmonization of tau PET imaging.

Sensory and pain outcomes of neurotized skin-grafted free gracilis muscle flaps for lower extremity reconstruction

BackgroundSkin-grafted free gracilis muscle flaps are commonly used for lower extremity reconstruction. However, the loss of sensory function may lead to increased patient morbidity. This study prospectively analyzed the sensory and neuropathic pain outcomes of neurotized skin-grafted free gracilis muscle flaps used for the reconstruction of lower extremity defects. MethodsPatients undergoing lower extremity reconstructions between 2020 and 2022 with neurotized skin-grafted free gracilis muscle flaps were prospectively enrolled. Sensation was assessed at 3, 6 and 12 months postoperatively using monofilaments, two-point discrimination, a vibration device, and cold and warm metal rods. Sensations were tested in the center and periphery of the flaps, as well as in the surrounding skin. The contralateral side served as the control. Patients completed the McGill pain questionnaire to evaluate patient-reported neuropathic pain. ResultsTen patients were included. At 12 months postoperatively, monofilament values improved by 44.5% compared to that of the control site, two-point discrimination, cold detection, warmth detection, and vibration detection improved by 36.2%, 48%, 50%, and 88.2%, respectively, at the reconstructed site compared to those at the control site. All sensory tests were significantly better than 3 and 6 months values (p < 0.05), but remained significantly poorer than the control site (p < 0.05). Sensation in the central flap areas were similar to peripheral flap areas throughout the follow-up period (p > 0.05). The surrounding skin reached values similar to the control site at 12 months (p > 0.05). Moreover, 50% of patients reported neuropathic pain at 3 months postoperatively, 40% at 6 months, and 0% at 12 months (p < 0.05). ConclusionMechanical detection, vibration detection, temperature detection, and two-point discrimination significantly improved over time but without reaching normal sensory function at 12 months postoperatively. Neuropathic pain resolved at 12 months.

Numerical investigation on critical heat flux for 5 × 5 fuel assemblies with a wide range of working conditions

To determine the safe boundary of fuel assembly operation and improve the heat transfer performance of fuel assembly, it is necessary to accurately calculate the thermohydraulic characteristics and the critical heat flux (CHF) in rod bundles. The Eulerian two-phase model coupled with extended wall boiling model was used to numerically investigate the 5 × 5 fuel rod bundle flows with four sets of mixing vane spacer grids. A wide range of working conditions were analyzed to validate the numerical method. The results indicate that the current numerical model can not only accurately calculate the CHF values but also predict the location of heat transfer crisis. Based on CFD (Computational Fluid Dynamics) results, the detailed two-phase flow distributions were provided to analyze the CHF performance under special structures, such as bowed rod and spacer backward shift. The quantitative results were obtained on the analyses of spacer position influence on CHF and the penalty effect of bowed rod. Furthermore, the prediction of present numerical model under low inlet subcooling conditions and cold rod CHF were discussed. The research of this paper provides support for the design and optimization of fuel assemblies.

Study of the dynamics of changes in the thermal conductivity coefficient of organic deposits

ABSTRACT Ensuring flow in an oil field is one of the most costly problems in oil production and transportation. The fight against the formation of paraffin deposits consists both in the application of methods for the prevention and removal of deposits, and in the modeling of this process. An important parameter for the application of some technologies for preventing the formation of deposits and modeling the temperature regime of the pipeline is the coefficient of thermal conductivity of these deposits. The paper presents a study of the influence of the thermal conductivity of organic deposits on the rate of their formation, measured for 5 hours at the Cold Rod installation. According to the research results, it was found that over time, the thermal conductivity of organic deposits increases, while the rate of deposit formation decreases significantly. This process is explained by an increase in temperature on the surface of deposits due to their compaction and displacement from the volume of the liquid phase. The results obtained are extremely important in modeling the process of deposit formation and modeling a number of technologies to combat them.

Study on the mixing performance of mixing vane grids and mixing coefficient by CFD and subchannel analysis code in a 5×5 rod bundle

Mixing Vane Grid (MVG) is one of the most important structures in fuel assembly due to its high performance in mixing the coolant and ultimately increasing Critical Heat Flux (CHF), which avoids the temperature rising suddenly of fuel rods. To evaluate the mixing performance of the MVG, a Total Diffusion Coefficient (TDC) mixing coefficient is defined in the subchannel analysis code. Conventionally, the TDC of the spacer grid is obtained from the combination of experiments and subchannel analysis. However, the processing of obtaining and determine a reasonable TDC is much challenging, it is affected by boundary conditions and MVG geometries. In is difficult to perform all the large and costing rod bundle tests. In this paper, the CFD method was applied in TDC analysis. A typical 5 × 5 MVG was simulated and validated to estimate the mixing performance of the MVG. The subchannel code was used to calculate the TDC. Firstly, the CFD method was validated from the aspect of pressure drop and lateral temperature distribution in the subchannels. Then the effect of boundary conditions including the inlet temperature, inlet velocities, heat flux ratio between hot and cold rods and the arrangement of hot and cold rods on MVG mixing and TDC were studied. The geometric effects on mixing are also carried out in this paper. The effect of vane pattern on mixing was investigated to determine which one is the best to represent the grid's mixing performance.

STUDY OF MAGNETIC ACTIVATORS (WITH INTERNAL AND EXTERNAL MAGNETS) TO IMPROVE THE PROCESSES OF OIL TRANSPORTATION THROUGH THE PIPELINE

This work is aimed at improving the rheological properties of high-paraffin oil during transportation through pipelines using physical and chemical processing of raw materials by magnetic, thermal and chemical treatment. The selectivity of the magnetic treatment effect depends on the composition of the oil mixture, and at the same time contributes to a significant improvement in the rheological properties of the studied oil mixtures by reducing their pour point, kinematic viscosity, paraffin deposits determined using the cold rod method and the pressure drop in the model pipeline.

A SIMIND Monte Carlo Simulation Study on CdTe and NaI (Tl) Thickness as Detectors of a Small Animal SPECT System

Purpose: Micro Single Photon Emission Computed Tomography (Micro-SPECT) system has recently been introduced on nuclear medicine in the preclinical and research in which NaI (Tl) and Cadmium Telluride (CdTe) are used as the gamma-ray detectors with more generally use of NaI (Tl). The present study aimed to evaluate different thicknesses of the NaI (Tl) and (CdTe) detectors on functional parameters of a micro-SPECT system.&#x0D; Materials and Methods: A Micro-SPECT system with CdTe semiconductor detector and a hexagonal parallel hole collimator with a hole diameter of 0.11 mm, high of 24.05 mm, and septal thickness of 0.016 mm was simulated by Simulating Medical Imaging Nuclear Detectors (SIMIND) Monte Carlo program. The system performance was assessed by comparing the functional parameters, including system efficiency, sensitivity, energy and spatial resolution with the NaI (Tl) detector. The simulated scans of a 99mTc point source, a digital micro-Jacszack phantom, and a voxelized MOBY mouse phantom with the system were prepared to evaluate image quality.&#x0D; Results: The functional parameters; sensitivity, efficiency, planar spatial resolution, and image contrast of CdTe detector were determined 1.4, 1.2, 1.7, and 1.8 times higher than those of NaI (Tl), respectively. Moreover, the calculated energy resolution of CdTe and NaI (Tl) detectors was obtained 6.2% and 10.2% at 141 KeV, respectively. In the filtered back projection (FBP) reconstructed images of the micro-Jacszack phantom, minimum detectable size of the cold rods with CdTe and NaI (Tl) detectors were obtained 0.79 mm and 0.95 mm, respectively.&#x0D; Conclusion: The imaging system with a 5.5 mm thickness CdTe detector provided better image quality and showed considerable efficiency.

Fracture mechanism of AISI 1025 rod shearing in automatic multi-stage cold forging and critical shearing speed

Experimental and numerical studies on shearing processes that focused on automatic multi-stage cold forging (AMSCF) are conducted to reveal the mechanisms of the fracture phenomena that occur in the cold rod shearing process in AMSCF. First, AISI 1025 (treated for AMSCF, specifically called SWCH25F) coil-rod of radius 17.5 mm was straightened and cut by an AMSCF machine at operating speeds of 20–90 rpm to elucidate the effects of speed on the surface quality of the sheared billet. Second, a universal testing machine was used in combination with a special shearing apparatus for experimental cold rod shearing to measure the shearing load-time (or stroke) curve and examine fracture mechanisms at sufficiently low speeds. Fractographical observations showed that speed clearly affects the cold shearing of a straightened coil-rod. The surfaces of billets sheared at low speeds showed clear evidence of ductile fracture, whereas those sheared at normal speeds did not. The experimental results were used in thermoviscoplastic finite element (FE) analysis together with the flow behaviors of the material in the cold-forging temperature range to explain the brittle fracture of the ductile material during cold coil-rod shearing in AMSCF. The concept of a critical coil-rod shearing speed for acceptable surface quality is presented.

Simulation of photomultiplier tube malfunction and its effect on SPECT imaging system

Ring artifact appears on the image from SPECT (Single Photon Emission Computed Tomography) imaging system is related to the uniformity. Generally, ring artifacts arose due to the poor performance of the photomultiplier tubes (PMT) in the gamma camera. If one of the PMT cannot perform optimally, defects known as ring artifacts on the image will occur. Detecting the position of the PMT malfunction is a challenge. To study the detection of ring artifacts due to PMT malfunction, artifact reconstruction was conducted by masking one of the PMT on the gamma camera using a copper sheet sizes 4 × 4 cm2 and thickness 1 mm. The position of the copper sheet was varied on the horizontal (x) and vertical (y) axes from the center of the detector. Jaszczak phantom without inserts (cold rods and sector cold rods) was used as an imaging object during acquisition. The image results obtained are ring artifact if the copper sheet is positioned on the (x,0), and half-ring artifact on the (0,y).

Influences of the Water Cut of Pumping Oil and the Mineralization of the Associated Water on the Rate of Sludging

The problem of the formation of organic deposits on the inside surfaces of borehole equipment and oilfield pipelines, which is urgent for all active oil fields, was considered in the study. The formation of these deposits leads to decreased lifespans for oilfield equipment and accidents involving oil pipelines and wells. The aim of our work was to estimate the dependencies of the organic deposition’s formation-rate factor on the water cut of the investigated water–oil emulsion and the mineralization of the water phase. Examination via generation of asphaltene–resin–paraffin deposits on the surfaces of cold rods was carried out with a “Cold Finger” CF-4 unit. Coefficients of specific oil sludging, fluid sludging and rate sludging have been determined. It has been defined that in the definite oilfields, the rate of sludging does not increase as the water content in the emulsion increases. As water-phase mineralization increases, this value remains practically constant.

Comparison and validation of automated scoring of SPECT phantom cold rod visibility.

Evaluation of phantom image quality is an integral component of the quality assurance of SPECT systems. This evaluation often is done by visual assessment of the resolution of known structures of a specified size, such as arrays of cold rods in a warm background. Although this method is rapid and convenient, it is qualitative and is subject to inter- and intraobserver variability. Thus an automated quantitative analysis would be preferable. Several metrics of cold rod visibility have been developed, although their suitability for SPECT quality assurance depends on how well they correspond to visual scoring by experienced observers. Various metrics of cold rod visibility, derived from either texture analysis or template-based analysis, were investigated. The texture analysis methods measured the normalized gray-level co-occurrence matrix (GLCM) energy ("Energy%") and entropy ("Entropy%") of each region and an associated combination of the two ("EnergyEntropy%"). One template-based method measured the rods-to-background contrast ("Contrast") and an associated visibility index (Contrast×area="Contrast Visibility"). Another template-based method performed binary classification (BC) of the rods and background to compute the area under curve (AUC) of its receiver operating characteristics (ROC) curve ("BC-AUC") and the corresponding signal-to-noise ratio ("BC-SNR"). All these metrics were computed for 90 SPECT acquisitions of the standard American College of Radiology ("Jaszczak") phantom. Cold rod visibility was scored independently by two experienced nuclear medicine physicists on both dichotomous and 5-point scales. Scoring was performed twice by each observer to evaluate variability. Interobserver agreement (Cohen's kappa statistic) was 0.78, and intraobserver reproducibility was 0.86 and 0.88, respectively, for each observer. Mean and median scores differed significantly between observers. Accuracy of each metric was assessed according to AUC of ROC analysis with respect to mean dichotomous score. The binary classification metrics had the highest accuracy (BC-AUC=0.995, BC-SNR=0.994), above that of the texture analysis metrics (Entropy%=0.992, Energy%=0.988, EnergyEntropy%=0.992) and conventional template analysis (Contrast=0.984, Contrast Visibility=0.989). The metrics were similar in terms of rank correlation to mean visibility score. BC-AUC correlated linearly with mean visibility score (R2 =0.95) and consistently performed among the highest of the metrics vs rod diameter and count level. Automated quantitative analysis of SPECT phantom cold rods correlated well with visual scoring. The metrics based on binary classification performed particularly well for this task, across the range of rod diameters and count levels. The suboptimal interobserver agreement highlights the importance of developing automated algorithms for evaluating scanner performance.

Epoxy thermoset coatings with fine controllable hierarchical structures prepared from bio-inspired photo-/colloidal lithography technique for anticorrosion application

Several epoxy thermoset (ET) composite coatings with artificial fine controllable micro/nano hierarchical structures were prepared through photolithography/colloidal lithography and subsequently applied in anticorrosion field. Firstly, several silicon wafers with fine controllable interspacing and width of micro-scaled cylindrical structures were fabricated through conventional photolithography. Subsequently, nano-scaled tips were fabricated upon a smooth clean surface on the previous silicon wafer with micro-scaled cylinders to generate nano-scaled tips through colloidal lithography. Moreover, ET coatings were duplicated by nano-casting technique with polydimethylsiloxane (PDMS) as a soft negative template. Surface morphology and contact angle (CA) of as-prepared hard silicon template and ET coatings were identified. The CA of water droplets on ET coating with bio-inspired micro/nano hierarchical structures (denoted by BET) was 160°, which meant that this coating was more hydrophobic than ET coatings with distinctive surface structures. Anticorrosion studies of as-prepared ET coating with/without distinctive structures showed that cold rod steel (CRS) electrode coated with BET had better anticorrosion performance than other ET coating for short- and long-term studies. This procedure of fine controllable micro/nano structure coatings opens the door for further innovative investigations of corrosion protection methods and material designs.

Numerical Investigation on Forced Hybrid Nanofluid Flow and Heat Transfer Inside a Three-Dimensional Annulus Equipped with Hot and Cold Rods: Using Symmetry Simulation

A 3D computational fluid dynamics method is used in the current study to investigate the hybrid nanofluid (HNF) flow and heat transfer in an annulus with hot and cold rods. The chief goal of the current study is to examine the influences of dissimilar Reynolds numbers, emissivity coefficients, and dissimilar volume fractions of nanoparticles on hydraulic and thermal characteristics of the studied annulus. In this way, the geometry is modeled using a symmetry scheme. The heat transfer fluid is a water, ethylene–glycol, or water/ethylene–glycol mixture-based Cu-Al2O3 HNF, which is a Newtonian NF. According to the findings for the model at Re = 3000 and ϕ1 = 0.05, all studied cases with different base fluids have similar behavior. ϕ1 and ϕ2 are the volume concentration of Al2O3 and Cu nanoparticles, respectively. For all studied cases, the total average Nusselt number (Nuave) reduces firstly by an increment of the volume concentrations of Cu nanoparticles until ϕ2 = 0.01 or 0.02 and then, the total Nuave rises by an increment of the volume concentrations of Cu nanoparticles. Additionally, for the case with water as the base fluid, the total Nuave at ϕ2 = 0.05 is higher than the values at ϕ2 = 0.00. On the other hand, for the other cases, the total Nuave at ϕ2 = 0.05 is lower than the values at ϕ2 = 0.00. For all studied cases, the case with water as the base fluid has the maximum Nuave. Plus, for the model at Re = 4000 and ϕ1 = 0.05, all studied cases with different base fluids have similar behavior. For all studied cases, the total Nuave reduces firstly by an increment of the volume concentrations of Cu nanoparticles until ϕ2 = 0.01 and then, the total Nuave rises by an increment of the volume concentrations of Cu nanoparticles. The Nuave augments are found by an increment of Reynolds numbers. Higher emissivity values should lead to higher radiation heat transfer, but the portion of radiative heat transfer in the studied annulus is low and therefore, has no observable increment in HNF flow and heat transfer.

Applicability of Solid Lubricant Coatings in Cold Rod Extrusion of Stainless Steels

Cold extrusion is an established technology for the production of dimensionally accurate components in large series. Due to the high material and energy efficiency, a resource-saving manufacturing of high-performance parts is possible. Forming at room temperature leads to an advantageous grain structure and work hardening of the material, resulting in components with favorable operating characteristics. Nevertheless, a challenge is the generation of residual stresses during forming, which are influencing the fatigue behavior. The modification of the tribological conditions is one method for influencing the parts’ residual stress state. However, the high strength and work hardening of the materials formed at room temperature leads to high tribological loads between billet and die. These challenges are intensified by the increasing use of stainless steels due to growing demands for corrosion resistant components. The aim followed within this paper is therefore to investigate the applicability of typical lubricant coatings in the forward rod extrusion of stainless steels. For this purpose, the ferritic stainless steel X6Cr17 (DIN 1.4016) and the ferritic-austenitic stainless steel X2CrNiMoN22-5-3 (DIN 1.4462) are extruded with an equivalent plastic strain of ε̅ ≈ 1. The research is performed with a molybdenum disulfide (MoS2), a soap and a polymer-based lubricant coating. For reproducing different contact conditions, the die geometry is varied with die opening angles of 60°, 90° and 120°. The suitability of the lubricants is evaluated using the integrity of the lubricant coating after forming. From the correlations between process forces, temperatures and surface integrity, recommendations for the application of the researched lubricants are derived.

Evaluation of the effect of new-synthesized heterocyclic compounds as inhibitors of ARP deposits

This article is devoted to the studying of the problem of the resin and asphaltene deposits formation in the process of oil production and transportation using the example of high-viscosity oil from the Ashalchinskoe field. The chemical method for the prevention and removal of ARPD, connected with the use of phosphorylated alkylphenols is considered in detail. Extraction of asphaltenes was carried out by selective dilution of the oil sample following by washing in Soxhlet apparatus. Hydrocarbon structure of asphaltenes was studied by the method of IR-spectroscopy on the spectrometer PerkinElmer. Paramagnetic characteristics of asphaltenes were analyzed by EPR method. Rheological properties of oil emulsion were studied by viscosimetry method using rotational viscometer One Touch Lamy Rheology. The graphs that indicate the dependence of the viscosity of oil emulsions on applied shear stress were plotted. The method of the “cold rod” was used to evaluate the inhibitory effect of the new organic compound.

SUBSTANTIATION AND SELECTION OF AN INHIBITOR FOR PREVENTING THE FORMATION OF ASPHALT-RESIN-PARAFFIN DEPOSITS

Currently, most oil fields are under the late stage of development, which is associated with some challenges during the production of reservoir products, including the formation of asphalt-resin-paraffin deposits (ARPD) in the “well – bottom-hole formation zone” system. Even though the problem of organic deposits creation has existed for more than 60 years, it is still relevant today. Currently, to prevent the formation of ARPD, inhibitors divided into methods based on the use of wetting agents, modifiers, depressors, and dispersants are widely used infield practice. The composition of inhibitors often includes surfactants, and according to field experience, nonionic surfactants, namely, polyesters, are widely used to prevent the formation of ARPD. However, little is known about inhibitors with a combined effect, for example, possessing depressor-dispersing properties concerning ARPD. Proceeding from the above, the work is aimed to develop a combined inhibitor with depressor-dispersing properties to prevent the formation of ARPD. The dispersing property of the prepared reagent for asphaltene particles was determined using capillary and photocolorimetric methods. The studies were conducted to assess the impact of the reagent on the freezing point. A quantitative assessment of the sedimentation process using the “Cold rod” installation was performed, and the results of studies of the developed ARPD reagent-inhibitor corrosion resistance were presented. Two methods determined the temperature of oil saturation with paraffin: the direct approach – visual observation (Axio Lab A1 microscope) and the indirect approach – rheogoniometry to determine the kinematic viscosity of oil (HVM-472 viscosity analyzer (Walter Herzog GmbH, Germany)). Thus, an ARPD inhibitor (IN-1), comprising a copolymer of ethylene with α-olefins or polymers of acrylic, methacrylic, or cyanoacrylic acid esters, an emulsifier of inverted oil-in-water emulsions and a solvent, was developed. The developed inhibitor, having depressor-dispersing properties, is capable of reducing oil-freezing point in winter and of slowing down the precipitation of paraffin crystals in well equipped and in the bottom-hole formation zone (BHFZ).

Influence of Current Waveforms on Single Discharge Crater in EDM

This paper describes the effects of the discharge-current waveform on the shape and removal volume of craters in electrical discharge machining (EDM). In EDM, it is known that removal efficiency, defined as the ratio of the removal volume to the volume molten by a single discharge, is no more than several percent. Hence, to increase the removal efficiency, the influence of the discharge current waveforms on the removal volume in a single discharge was investigated. Using cold tool steel plates and copper rods as the workpiece and tool electrode, respectively, the removal volume of workpiece with the polarity of positive was largest when a linearly increased and sharply turned off current was used with the pulse duration of 200μs.

Assessment of PET and SPECT phantom image quality through automated binary classification of cold rod arrays.

Evaluation of positron emission tomography (PET) or single photon emission computed tomography (SPECT) performance often involves qualitative assessment of phantom images, namely the visibility of hot or cold structures in a warm background. Structure-to-background contrast is a quantitative measure of scanner performance; however, contrast measurements do not account for image noise and its effect on task performance. Although task-based performance could be evaluated over an ensemble of phantom scans, a more practical approach is desired. Repeated structures, such as the cold rod arrays of the American College of Radiography (ACR) PET and SPECT phantoms, offer an opportunity to evaluate image quality based on statistical decision theory. Images are co-registered to a digital template for placement of numerous regions of interest (ROIs) in multiple thick slices centered on each cold rod and on each midpoint between rods. The assumption is made that each ROI corresponds to a statistically independent measurement, known to be of either a cold rod or the background. A receiver operating characteristic (ROC) curve then is generated for each cold rod sector of the phantom. The area under the ROC curve (AUC) provides a quantitative measure of cold rod visibility. In addition, signal-to-noise ratio (SNR) is calculated, under the assumption that the rod and background ROI measurements are distributed normally. Using this approach, data from PET and SPECT phantom studies from prior annual physics surveys were analyzed retrospectively. Rod and background ROI measurements had nearly normal (PET) or approximately normal (SPECT) distributions. Resultant ROC curves illustrated the varying degrees of overlap between rod and background histograms vs cold rod diameter. Both AUC and SNR correlated well with visual image assessment and had high consistency between phantom studies, demonstrating the quantitative accuracy of the automated analysis. AUC reliably quantified cases where cold rods were partially or mostly resolved, while SNR provided further characterization when cold rods were completely resolved. In comparison, contrast measurements often mirrored AUC and SNR but were inconsistent in cases of varying noise. Automated analysis of phantom cold rod arrays using binary classification provides informative quantitative measures of image quality and is practical for routine use. This approach avoids observer dependencies associated with visual assessment and potentially can benefit quality assurance, physics surveys, laboratory accreditation, and harmonization of multicenter image quality.

Automated Quantitative Analysis of American College of Radiology PET Phantom Images

Evaluation of PET image quality is central to annual physics surveys, quality assurance, and laboratory accreditation. A common method is to image the American College of Radiology (ACR) PET phantom, which contains hot and cold structures of various sizes in a warm background. Performance evaluation involves qualitative assessment of hot and cold structure visibility and overall image quality. Some criteria are quantitative and rely on manually drawn regions of interest (ROIs) to measure SUV. Fully automated scoring of ACR PET phantom images would improve efficiency, avoid observer-related dependencies, and possibly provide more robust evaluation of image quality. Methods: Software was developed to coregister PET images to a phantom template and to compute ROI measurements of hot vial activity (SUVmax) and background activity (SUVmean) automatically. In addition, 3-dimensional volumes of interest (VOIs) were generated to measure hot vial activity (SUVvial), background activity, and cold rod contrast. Consistency of the ROI-based and VOI-based methods was evaluated using phantom data from a total of 17 annual physics surveys of 3 PET/CT scanners with the same PET detector design. Results: The automated software processed all PET phantom datasets successfully. SUV consistency for hot vials was improved through use of cylindric VOIs and through normalization with respect to assayed activities and dilution volumes used in phantom preparation. Average vial SUV SD improved from 8.0% for standard SUVmax to 3.2% for normalized SUVvial Similarly, the SD for the SUV ratio of 16- to 25-mm vials improved from 5.0% for SUVmax to 3.2% for SUVvial Background SUVmean had a similar consistency between the ROI and VOI methods. Cold rod contrast was highly consistent, offering a potential alternative to qualitative visual assessment of low-contrast performance. Conclusion: Automated quantitative scoring of the ACR PET phantom is feasible and offers the advantages of more efficient, consistent, and thorough performance characterization. Acceptance ranges for SUVs and ratios likely can be tightened if normalized VOI measurements are used. Further testing with phantom data from a variety of PET scanners is necessary to establish suitable quantitative thresholds for acceptable performance.

3D CFD simulation of a Vuilleumier heat pump

A 3D CFD simulation has been conducted in order to investigate the thermodynamic and flow characteristics of a Vuilleumier heat pump. Vuilleumier heat pumps are machines with few components which need a heat source of high temperature to operate and in some cases additionally some work input. The simulated machine comprises of one cylinder inside which two displacers reciprocate. The design of the machine resembles two opposing GPU-3 Stirling engines which is an existing engine and it was based on calculations conducted with the use of a 1D analytical mathematical model. The CFD simulation run for several cycles until convergence was established and yielded the spatial and temporal distribution of the temperature, pressure and velocity inside the several spaces of the heat pump. The pressure drop along the components of the heat pump was calculated and also the flow reversal time instances at the interfaces where adjacent components coincide. Other mathematical models used in the past couldn’t provide information neither about the flow direction everywhere inside the machine nor about the opposing flow streams inside the common compression space. Moreover, the CFD model provided the heat quantities entering or exiting the heat pump. The two heat exchangers that are placed in order to absorb heat, resulted to reject heat for a small time period during the cycle from a section of their body. Furthermore, the heat flow did not follow strictly the temperature difference between the bulk gas and the solid wall. It was driven by the temperature difference between the gas near the wall and wall. This discrepancy indicates a counter flow inside the tubes of the heat exchangers. Finally, it was expected that the CFD machine would require an amount of work to operate, because it was designed based on an analytical model without losses. So, the CFD simulation, which includes pressure drop losses, resulted to require additional external work, which can be minimized designing a thick cold displacer rod.