Hot Rod Research Articles

Simulation study of a novel target oriented SPECT design using a variable pinhole collimator.

In the past decade, demands for organ specific (target oriented) single-photon emission computed tomography (SPECT) is increasing, and several groups have conducted studies on developing clinical dedicated SPECT with pinhole collimator to improve the spatial resolution. However, acceptance angle of the collimator cannot be adjusted to fit the different ROIs of target objects because the shape of pinhole could not be changed, and the magnifying factor cannot be maximized as the collimator-to-detector distance is fixed. Furthermore, those dedicated pinhole SPECTs are typically made for a single purpose and therefore possess a drawback in that it cannot be utilized for any other purpose. In this study, we propose a novel SPECT system using variable pinhole collimator (VP SPECT) whose parameters are flexible. The proposed variable pinhole collimator is modeled on conventional pinhole by piling several tungsten layers of different apertures. Depending on the combination of the holes in each layer, a variety of hole diameters and acceptance angles of the pinhole can be made. In addition, VP SPECT system allows attaching the collimator to the object as close as possible to maximize the sensitivity and adjust the distance of the pinhole from the scintillation detector to optimize the system resolution for each rotation angle, automatically. For quantitative measurement, we compared the sensitivity and spatial resolution of VP SPECT with those of conventional pinhole SPECT. To determine the possibility of the clinical and preclinical use of proposed system, a digital mouse whole-body (MOBY) phantom is used for simulating the live mouse model. The result of simulation using ultra-micro hot spot phantom shows that the sensitivity of the proposed VP SPECT system is about 297% of that of the conventional system. While hot rods of diameter 0.6mm can be distinguished in the image with the proposed VP SPECT system, 1.2-mm hot rods are barely discernible in the conventional pinhole SPECT image. According to the result of MOBY phantom simulation, heart walls separated by 3mm were not distinguished in conventional pinhole SPECT images, but were clearly discerned in VP SPECT images. In this study, we designed a novel pinhole collimator for SPECT and presented preliminary results of target oriented imaging with a simulation study. Currently, we are pursuing strategies to realize the proposed system, with the goal to apply the technology into a high-sensitivity and high-resolution preclinical SPECT. Should VP SPECT be applied to the clinical setting, we anticipate a high-sensitivity, high-resolution system for applications such as heart dedicated SPECT or related fields.

The Influence of the Deformation Degree on the Mechanical Properties and Microstructures of the Blanks Obtained by Tube and Wire Drawing

In this paper is describe the influence of the deformation degree on the mechanical properties and microstrucure of the blanks obtained by tube and wire drawing. The materials used for this study are represented by two different samples: hot rolled wire rod and wire for concrete reinforcement with periodic profile (drawn wire) with three dimensions of obtained diameter ( d1 = 5.00 mm, d2= 4 mm and d3= 3,5 mm). The results reveal that the strength properties of the samples are increasing with an increase in the degree of deformation, while the plasticity properties are lowering.The purpose of this paper is to evidence the changes in the structure, the strength and plasticity properties depending on the deformation degree and section reducing of the metallic material.

A Goal-Oriented, Sequential, Inverse Design Method for the Horizontal Integration of a Multistage Hot Rod Rolling System

The steel manufacturing process is characterized by the requirement of expeditious development of high quality products at low cost through the effective use of available resources. Identifying solutions that meet the conflicting commercially imperative goals of such process chains is hard using traditional search techniques. The complexity in such a problem increases due to the presence of a large number of design variables, constraints and bounds, conflicting goals and the complex sequential relationships of the different stages of manufacturing. A classic example of such a manufacturing problem is the design of a rolling system for manufacturing a steel rod. This is a sequential process in which information flows from first rolling stage/pass to the last rolling pass and the decisions made at first pass influence the decisions that are made at the later passes. In this context, we define horizontal integration as the facilitation of information flow from one stage to another thereby establishing the integration of manufacturing stages to realize the end product. In this paper, we present an inverse design method based on well-established empirical models and response surface models developed through simulation experiments (finite-element based) along with the compromise decision support problem (cDSP) construct to support integrated information flow across different stages of a multistage hot rod rolling system. The method is goal-oriented because the design decisions are first made based on the end requirements identified for the process at the last rolling pass and these decisions are then passed to the preceding rolling passes following the sequential order in an inverse manner to design the entire rolling process chain to achieve the horizontal integration of stages. We illustrate the efficacy of the method by carrying out the design of a multistage rolling system. We formulate the cDSP for the second and fourth pass of a four pass rolling chain. The stages are designed by sequentially passing the design information obtained after exercising the cDSP for the last pass for different scenarios and identifying the best combination of design variables that satisfies the conflicting goals. The cDSP for the second pass helps in integrated information flow from fourth to first pass and in meeting specified goals imposed by the fourth and third passes. The end goals identified for this problem for the fourth pass are minimization of ovality (quality) of rod, maximization of throughput (productivity), and minimization of rolling load (performance and cost). The method can be instantiated for other multistage manufacturing processes such as the steel making process chain having several unit operations.

CFD Study on Emergency Core Cooling of Hot Vertical Nuclear Fuel Rod Bundle by Jet Impingement

The rewetting is the process of re-establishment of coolant with hot surfaces. This rewetting characteristic influence on cooling of nuclear rod bundles was conducted using CFD-CFX code. The numerical results are compared with experimental result and achieved good agreement. The present study intended in the prediction of rewetting behavior in rod bundle. It is observed that the rewetting behavior was significantly affected by phase distribution. It is seen that the peak rewetting temperature appears in the vapor region. The wetting delay is negligible at inlet section, but longer period is observed in others section of the rod bundle. It was noted that the complication of rewetting regimes is due to the uneven and irregular flow of coolant which affect re-establishment of coolant into hot surface.

Hot iron rods branding, its complications: Still continue in central India

Introduction: The middle of the 20th century has often been described as a golden age of scientific advancement and miraculous medical breakthroughs. In spite of a lot of awareness and many health education programs, still some traditional treatment exists in many places in our country including Central India. In some villages of Madhya Pradesh, many horrifying therapies such as iron rods branding are well known for a few common diseases such as ascites, headache, pneumonia, common cold, or hernia. Bruise marks can be seen on the bodies of a majority of villagers. Main reasons behind such therapy are lack of money for medical treatment, lack of medical facilities, and the unwillingness of medical officers to stay in small villages. Besides this, illiteracy compels them to follow old customs and practices. All these strengthen the faith of villagers in such treatments. It is all due to lack of education and proper awareness. Many female patients come to hospital with complications of iron rods branding suggest that despite being educated, strong cultural beliefs forces people to undergo branding as a treatment of many common diseases in India even in the 21st century. Aims and Objectives: To study the reasons and complications of hot iron branding. Materials and Methods: Sample size was 30. Thirty patients with old, healed (within 1 year), or recent scars of iron branding were included in the study. Patients were evaluated for the sociodemographic details and the information of underlying disease, pattern of lesions, and complications of branding. Results: Hot iron branding is still carrying on as traditional treatment in Central India. It is commonly seen in females of age 20–50 years. It is mostly found in illiterate patients of low socioeconomic status who have chronic disease and chronic pain. Conclusion: Skin branding which still has therapeutic uses in some cultural societies have severe medical complications in Central India.

Performance characteristics of the MAMMOCARE PET system based on NEMA standard

In this work, we present the performance characteristics of the MAMMOCARE PET prototype based on an adaptation of the NU 4-2008 NEMA standard. MAMMOCARE is a project under the European Commission's 7th Framework programme to develop a breast biopsy system guided by a dedicated breast PET (dbPET) images. The PET system is formed by two rings with twelve detector modules each. The transaxial FOV is 170 mm and the axial FOV is 94 mm. The system can separate the detectors up to 60 mm in transaxial plane to allow the biopsy needle entrance. The acquisitions are reconstructed using the LMOS algorithm with tube-of-response (TOR) backprojector, 1 iteration and 16 subsets. The voxel and pixel sizes are (1 × 1 × 1) mm3 and (1.6 × 1.6) mm2 respectively. The radial resolution measured is 1.62 mm in the center of the FOV and 3.45 mm at 50 mm off the center in the radial direction using the closed configuration. In the open configuration the resolution reaches 1.85 mm and 3.65 mm at center and at 50 mm off-center. The adapted recovery coefficients (ARC) are measured for six hot rods inside a cylindrical phantom with a warm background. The ratio between hot and background regions is 10. The ARC values for the closed configuration are 0.32, 0.77 and 0.96 for the inserts with a diameter of 4.5 mm, 8.3 mm and 25 mm, respectively. These values decrease to 0.16, 0.52 and 0.77 for the open configuration. The sensitivity measured using an energy window of 250 keV–750 keV is 3.6% and 2.5% for the closed and open configurations respectively. The NEC peak is 141 kcps@68 MBq and 147 kcps@78 MBq for closed and open configurations. The performance characteristics measured with the open ring configuration decreases with respect the closed configuration, however the values remain comparable to other dbPETs.

A harmful traditional practice in newborns with adrenocorticotropic hormone resistance syndrome: branding

Branding refers to a traditional practice of creating 'therapeutic' burns with hot iron rods over the skin in order to treat various diseases. Although branding is a harmful practice for the body, it has been used for various illnesses including physiologic jaundice in newborns, pneumonia, and convulsions. It causes serious morbidity and delays seeking proper medical care in neonates. Innovations of modern medicine and the use of evidence-based medicine should be preferred instead of these traditional practices. We present a branded mature newborn baby who was diagnosed as having adrenocorticotropic hormone resistance syndrome. This problem is very rare in Turkey; however, it is a very important health issue and has social aspects. Therefore, this case is presented to increase awareness.

Neutronic study of a new generation of the small modular pressurized water reactor using Monte-Carlo simulation

Small Modular Reactors (SMRs) are the innovative design of nuclear reactors making remarkable interest during recent years. Since there is not enough available operating experience on SMRs, it might be possible to initiate extensive investigations on these types of reactors for the purpose of improving the current performance level of these systems, significantly. The main purpose of this present study is neutronic study of a typical small modular pressurized water reactor via Monte-Carlo method using the MCNPX code. The CAREM25 is chosen as the reference SMR. The reactor core geometry is simulated and neutronic parameters are visualized and analyzed via high qualified 3-D figures. They are figure out neutronic nature of the chosen case study. They capture the simulation of the reactor core geometry, and skim the neutron flux and power distribution, radial and axial power peaking factors and the influence of the control rods on the thermal flux. Central fuel assembly is determined as the hottest fuel assembly with power peaking factor of 1.778. The hottest fuel rod power peaking factor is calculated as 1.846 in the hottest assembly. The maximum calculated axial power peaking factor of the hot rod is 2.85. Results show that the maximum axial power along the fuel rods occurred below the mid-plane of the rod. The ratio of the hot to average rod axial power peaking factor as a safety parameter used to calculate the maximum heat flux in the hottest channel, is calculated close to 2 in almost 70% of the core height.The core reactivity at cold and hot shut down without safety injections of boron acid is calculated as 0.09712(Δkk) and −0.00103(Δkk), respectively.Results show suitable neutronic behavior and responses during virtual tests and analyses.

Impact of fuel thermal conductivity degradation on Doppler feedback during rod ejection accident

This paper discusses the importance of the fuel thermal conductivity degradation modeling for accurate predictions of the Doppler feedback during reactivity insertion transients. The impact of the fuel thermal conductivity degradation model, recently implemented in the coupled sub-channel thermal-hydraulic/time-dependent neutron transport code system CTF/TORT-TD, on Doppler feedback predictions during a control rod ejection accident was investigated. The rod ejection was simulated for a 4×4 pressurized water reactor pin array, extracted from the Purdue University MOX (mixed oxide) benchmark, starting at both hot zero power and hot full power conditions with the control rod being half-inserted before the ejection. The two scenarios were simulated with CTF/TORT-TD and the effect of the fuel thermal conductivity degradation on the Doppler feedback was analyzed. The results were compared with existing reference calculations performed with the coupled sub-channel thermal-hydraulic/time-dependent neutron transport/fuel performance code system CTF/TORT-TD/FRAPCON-FRAPTRAN.The power pulse, the time evolution of average fuel temperature, and the peak enthalpy rise during the transient were examined. It was confirmed that the impact of the fuel thermal conductivity degradation is more significant when the control rod is ejected at hot full power conditions. If the fuel conductivity degradation was not taken into account, less conservative CTF/TORT-TD predictions for the transient power response were obtained. For the selected 4×4 pin array, the coupled code calculated 13MW higher power pulse when modeling degradation effects on fuel conductivity. The difference in the power response is due to the less negative prompt fuel temperature (Doppler) coefficient at elevated temperatures. Lower thermal conductivity will lead to higher fuel pellet temperatures, and subsequently to a less negative Doppler coefficient, which will result in a stronger power pulse. The maximum fuel enthalpy rise during the hot full power rod ejection accident was found to be 60cal/g (251,208J/kg).

A high-temperature stable ceramic-coated separator prepared with polyimide binder/Al2O3 particles for lithium-ion batteries

An effective and practical way to develop the lithium-ion power batteries with better safety performance is to increase the thermal shrinkage resistance of the separator at high temperature. In this work, a ceramic coating separator (CCS-PI) is manufactured by coating Al2O3 ultrafine powder and thermal stable polyimide binder onto the surface of the porous polyethylene (PE) membrane. CCS-PI exhibits no thermal shrinkage up to 160°C in dry state and maintains stable when packed inner the cells up to 165°C. Meanwhile CCS-PI hasn't been punctured during the hot metal rod piercing testing. The above results all prove that the CCS-PI has high thermo-stability. In addition, the CCS-PI presents higher electrolyte uptake, better wettability with the electrolyte and enabled high ionic conductance when it is saturated with liquid electrolyte. The cells with this CCS-PI show good cyclic performance. Therefore, as-prepared CCS-PI is a promising separator to improve thermal safety and capacity retention for lithium-ion power batteries.

CFD analysis of rewetting vertical nuclear fuel rod by dispersed fluid jet impingement

Summary Numerical analysis of cooling assessment in hot vertical fuel rod is carryout using ANSYS 14.0 – CFX Solver. Rewetting is the process of re-establishment of coolants with hot surfaces. Numerical validation exercise carried out with number of turbulence and shear stress turbulence model fairly predict the experimental data and used for further investigation. In the present paper, dispersed fluid is simulating with CFX solver to investigate the flow boiling process in emergency cooling of vertical fuel rod. When coolants come in contact on the hot surface this may not initiated the wetting patch. However, this paper introduces the unique jet impingement direction to remove the heat from the hot surface. In this report, the rewetting temperature and wetting delay also described during in progress of wetting front movement in hot vertical rod.

A heat transport benchmark problem for predicting the impact of measurements on experimental facility design

This work presents the application of the “Predictive Modeling of Coupled Multi-Physics Systems” (PM_CMPS) methodology conceived by Cacuci (2014) to a “test-section benchmark” problem in order to quantify the impact of measurements for reducing the uncertainties in the conceptual design of a proposed experimental facility aimed at investigating the thermal-hydraulics characteristics expected in the conceptual design of the G4M reactor (GEN4ENERGY, 2012). This “test-section benchmark” simulates the conditions experienced by the hottest rod within the conceptual design of the facility's test section, modeling the steady-state conduction in a rod heated internally by a cosinus-like heat source, as typically encountered in nuclear reactors, and cooled by forced convection to a surrounding coolant flowing along the rod. The PM_CMPS methodology constructs a prior distribution using all of the available computational and experimental information, by relying on the maximum entropy principle to maximize the impact of all available information and minimize the impact of ignorance. The PM_CMPS methodology then constructs the posterior distribution using Bayes’ theorem, and subsequently evaluates it via saddle-point methods to obtain explicit formulas for the predicted optimal temperature distributions and predicted optimal values for the thermal-hydraulics model parameters that characterized the test-section benchmark. In addition, the PM_CMPS methodology also yields reduced uncertainties for both the model parameters and responses.As a general rule, it is important to measure a quantity consistently with, and more accurately than, the information extant prior to the measurement. For the test-section benchmark, it is shown that the maximum coolant and rod surface temperatures responses are the most important measurable quantities. Using all of the available information, the PM_CMPS formulas yield optimally predicted best-estimate nominal model parameter values and reduced predicted standard deviations for the predicted parameters, such that: (i) the model parameters displaying the largest relative sensitivities and largest relative standard deviations are affected the most; and (ii) the model parameters with zero sensitivities remain unaffected by applying the PM_CMPS methodology. The PM_CMPS formulas also yield optimally predicted best-estimate nominal values for the model responses, along with correspondingly reduced predicted standard deviations.Assimilating within the PM_CMPS methodology an accurate measurement of the benchmark's maximum coolant temperature has the following impacts on the quantity that has been measured (i.e., on the maximum coolant temperature): (i) the nominal value of the predicted maximum coolant temperature is closer to the more “accurate” experimental value; (ii) the originally computed standard deviation is decreased significantly. In addition, the measurement of the maximum coolant temperature impacts not only the quantity being measured, but also impacts the other responses of interest, e.g., the maximum temperature in the rod and the maximum rod surface temperature. In all cases, the predicted standard deviations were decreased substantially, indicating that the predicted values are more accurate than the originally computed ones.The PM_CMPS formulas were also used to predict the impact of the simultaneous assimilation of the maximum coolant and the maximum rod's surface temperature measurements. As expected in view of the fact that the PM_CMPS methodology uses Bayes’ theorem to combine information, the assimilation of two accurate experiments reduces the predicted standard deviations of the maximum rod, rod surface and coolant temperatures even further. The test-section benchmark and methodology presented in this work can serve as a paradigm for quantifying the impact of experimental measurements in the analysis, design and/or operation of other thermal-hydraulics experimental facilities.

Development of correction methods for variable pinhole single-photon emission computed tomography

We propose a novel pinhole collimator in which the pinhole shape can be changed in real-time, and a new single-photon emission computed tomography (SPECT) system that utilizes this variable pinhole (VP) collimator. The acceptance angle and distance between the collimator and the object of VP SPECT are varied so that the optimum value of the region-of-interest (ROI) can be obtained for each rotation angle. Because of these geometrical variations, new correction methods are required for image reconstruction. In this study, we developed two correction methods. The first is the sensitivity-correction algorithm, which minimizes the variation of a system matrix caused by varying the acceptance angle for each rotation angle. The second is the acquisition-time-correction method, which reduces the variation of uniformity caused by varying the distance between the collimator and the object for each rotation angle. A 3D maximum likelihood expectation maximization (MLEM) algorithm was applied to image reconstruction, and two digital phantoms were studied to evaluate the resolution and sensitivity of the images obtained using the proposed methods. The images obtained by using the proposed correction methods show higher uniformity and resolution than those obtained without using these methods. In particular, the results of the resolution phantom study show that hot rods (0.8-mm-diameter) can be clearly distinguished using the proposed correction methods. A quantitative analysis of the ROI phantom revealed that the mean square error (MSE) was 0.42 without the acquisition-time-correction method, and 0.04 with the acquisition-time-correction method. The MSEs of the resolution phantom without and with the acquisition-time-correction method were calculated as 55.14 and 14.69, respectively.

Evaluation of Simultaneous Dual-radioisotope SPECT Imaging Using (18)F-fluorodeoxyglucose and (99m)Tc-tetrofosmin.

Objective(s):Use of a positron emission tomography (PET)/single-photon emission computed tomography (SPECT) system facilitates the simultaneous acquisition of images with fluorine-18 fluorodeoxyglucose (18F-FDG) and technetium (99mTc)-tetrofosmin. However, 18F has a short half-life, and 511 keV Compton-scattered photons are detected in the 99mTc energy window. Therefore, in this study, we aimed to investigate the consequences of these facts.Methods:The crosstalk correction for images in the 99mTc energy window involved the dual energy window (DEW) subtraction method. In phantom studies, changes in the count of uniform parts in a phantom (due to attenuation from decay), signal detectability in the hot-rod part of the phantom, and the defect contrast ratio in a cardiac phantom were examined.Results:For 18F-FDG in the step-and-shoot mode, nearly a 9% difference was observed in the count of projection data between the start and end positions of acquisition in the uniform part of the phantom. Based on the findings, the detectability of 12 mm hot rods was relatively poor. In the continuous acquisition mode, the count difference was corrected, and detectability of the hot rods was improved. The crosstalk from 18F to the 99mTc energy window was approximately 13%. In the cardiac phantom, the defect contrast in 99mTc images from simultaneous dual-radionuclide acquisition was improved by approximately 9% after DEW correction; the contrast after correction was similar to acquisition with 99mTc alone.Conclusion:Based on the findings, the continuous mode is useful for 18F-FDG acquisition, and DEW crosstalk correction is necessary for 99mTc-tetrofosmin imaging.

Chemical analysis of racing fuels using total vaporization and gas chromatography mass spectrometry (GC/MS)

The National Hot Rod Association (NHRA) is the governing body of North American drag racing.

Numerical Simulation of Polysilicon Chemical Vapor Deposition in Siemens Reactor

The Siemens CVD reactor should be refined when addressing the low energy consumption requirement for the production of solar grade polysilicon. The object of this paper is to investigate the heat transfer in Siemens reactor, which will provide the theoretical guidance for saving energy of polysilicon scale production. Based on Discrete Ordinates (DO) radiation model, an analysis is presented which studies the radiation exchange between the hot polysilicon rods and the cold reactor wall of four typical reactor configurations, especially the variation of the average power emitted per rod under various conditions of different rod diameter and wall emissivity. The results show that the energy consumption can be reduced by decreasing the emissivity of the reactor wall and enlarging the reactor capacity.

The environmental impacts of iron and steel industry: a life cycle assessment study

This study conducts a life cycle assessment for iron and steel production in Turkey using SimaPro software and IMPACT 2002+ impact assessment method with the purpose of comparing the impacts of processes (coke making, sintering, iron making, steel making) and final products (billet, slab, hot rolled wire rod, hot rolled coil), concurrently. System boundary was set as cradle-to-gate and functional unit was selected as 1 ton of final steel product. Among the processes, steel making process exhibited the highest total environmental impact, which was followed by sintering. The highest impacts were in the categories of human health and climate change. Coke production process showed the highest impact on depletion of non-renewable energy sources while it was with a negative contribution in the climate change category because of the avoided external energy consumption due to the production of coke oven gas within the facility. The comparison of the impacts for different final products revealed that hot rolled coil causes the highest total environmental impact followed by hot rolled wire rod, billet and slab. In an attempt to evaluate the effect of having different production scenarios implemented in the facility, three different scenarios representing three different production ratios of semi-finished (billet and slab) and finished (wire rod and coil) products were considered and it was found that the highest impact would come out if all the products were the finished ones and the hot rolling of casting products covers approximately 24% of the total environmental impacts of the full production cycle of one ton of product. Based on the assessment results, suggestions for sustainable production were made.

Performance Evaluation and Initial Clinical Test of the Positron Emission Mammography System (PEMi)

A new polygon positron emission mammography imaging system (PEMi) was developed in 2009 by the Institute of High Energy Physics, Chinese Academy of Sciences. PEMi is constructed in a polygon structure with lutetium yttrium orthosilicate crystal arrays mounted on a position-sensitive photomultiplier. The system consists of 64 blocks and each block is arranged in $16 \times 16$ crystal arrays with a pixel size of $1.9~\times 1.9~ \times 15$ mm. The diameter of the detector ring is 166 mm, and the axial length is 128 mm. The transaxial field of view of PEMi is 110 mm. The goal of the initial study was to test PEMi’s performance and the clinical imaging ability with a small group of selected subjects. The detectors have a measured intrinsic spatial resolution averaging 1.67 mm. The axial and tangential resolution remained under 2.5-mm full width at half maximum within the central 5-cm diameter of the field of view. The hot rods with a diameter of 1.7 mm can be clearly identified, and the structure of the region containing 1.35-mm diameter rods can also be observed. Using a 6-ns coincidence timing window and a ${\hbox {360}} \sim {\hbox {660}}$ -keV energy window, the peak sensitivity of the tomograph is 6.88%. The noise-equivalent count rate peak is 110 $\thinspace$ 766 cps for a breast-like cylindrical phantom of 100 mm in diameter at an activity concentration of $0.03~\hbox{MBq}/{\rm cc}$ . The recovery coefficients ranged from 0.21 to 0.85 for rods between 1 mm and 5 mm in the image-quality phantom. The reconstructed image resolution achieved an improvement compared with whole-body positron emission tomography (PET), which might reduce the lower threshold on detectable lesion size. Example patient images demonstrate that PEMi is clinically feasible. And more detailed structure information was obtained with PEMi than with the whole-body PET imaging.

Enhanced PET resolution by combining pinhole collimation and coincidence detection

Spatial resolution of clinical PET scanners is limited by detector design and photon non-colinearity. Although dedicated small animal PET scanners using specialized high-resolution detectors have been developed, enhancing the spatial resolution of clinical PET scanners is of interest as a more available alternative. Multi-pinhole 511 keV SPECT is capable of high spatial resolution but requires heavily shielded collimators to avoid significant background counts. A practical approach with clinical PET detectors is to combine multi-pinhole collimation with coincidence detection. In this new hybrid modality, there are three locations associated with each event, namely those of the two detected photons and the pinhole aperture. These three locations over-determine the line of response and provide redundant information that is superior to coincidence detection or pinhole collimation alone. Multi-pinhole collimation provides high resolution and avoids non-colinearity error but is subject to collimator penetration and artifacts from overlapping projections. However the coincidence information, though at lower resolution, is valuable for determining whether the photon passed near a pinhole within the cone acceptance angle and for identifying through which pinhole the photon passed. This information allows most photons penetrating through the collimator to be rejected and avoids overlapping projections. With much improved event rejection, a collimator with minimal shielding may be used, and a lightweight add-on collimator for high resolution imaging is feasible for use with a clinical PET scanner. Monte Carlo simulations were performed of a 18F hot rods phantom and a 54-pinhole unfocused whole-body mouse collimator with a clinical PET scanner. Based on coincidence information and pinhole geometry, events were accepted or rejected, and pinhole-specific crystal-map projections were generated. Tomographic images then were reconstructed using a conventional pinhole SPECT algorithm. Hot rods of 1.4 mm diameter were resolved easily in a simulated phantom. System sensitivity was 0.09% for a simulated 70-mm line source corresponding to the NEMA NU-4 mouse phantom. Higher resolution is expected with further optimization of pinhole design, and higher sensitivity is expected with a focused and denser pinhole configuration. The simulations demonstrate high spatial resolution and feasibility of small animal imaging with an add-on multi-pinhole collimator for a clinical PET scanner. Further work is needed to develop geometric calibration and quantitative data corrections and, eventually, to construct a prototype device and produce images with physical phantoms.

Technical Note: Characterization of custom 3D printed multimodality imaging phantoms.

Imaging phantoms are important tools for researchers and technicians, but they can be costly and difficult to customize. Three dimensional (3D) printing is a widely available rapid prototyping technique that enables the fabrication of objects with 3D computer generated geometries. It is ideal for quickly producing customized, low cost, multimodal, reusable imaging phantoms. This work validates the use of 3D printed phantoms by comparing CT and PET scans of a 3D printed phantom and a commercial "Micro Deluxe" phantom. This report also presents results from a customized 3D printed PET/MRI phantom, and a customized high resolution imaging phantom with sub-mm features. CT and PET scans of a 3D printed phantom and a commercial Micro Deluxe (Data Spectrum Corporation, USA) phantom with 1.2, 1.6, 2.4, 3.2, 4.0, and 4.8 mm diameter hot rods were acquired. The measured PET and CT rod sizes, activities, and attenuation coefficients were compared. A PET/MRI scan of a custom 3D printed phantom with hot and cold rods was performed, with photon attenuation and normalization measurements performed with a separate 3D printed normalization phantom. X-ray transmission scans of a customized two level high resolution 3D printed phantom with sub-mm features were also performed. Results show very good agreement between commercial and 3D printed micro deluxe phantoms with less than 3% difference in CT measured rod diameter, less than 5% difference in PET measured rod diameter, and a maximum of 6.2% difference in average rod activity from a 10 min, 333 kBq/ml (9 μCi/ml) Siemens Inveon (Siemens Healthcare, Germany) PET scan. In all cases, these differences were within the measurement uncertainties of our setups. PET/MRI scans successfully identified 3D printed hot and cold rods on PET and MRI modalities. X-ray projection images of a 3D printed high resolution phantom identified features as small as 350 μm wide. This work shows that 3D printed phantoms can be functionally equivalent to commercially available phantoms. They are a viable option for quickly distributing and fabricating low cost, customized phantoms.