Hot Spheres Research Articles

61 Evaluation and comparison of a new low energy high resolution collimator

Introduction In order to find an optimum compromise between spatial resolution and sensitivity, GEHC designed a new collimator (LEHRS) and combined it to a new acquisition software for planar images (Clarity2D) and to a new tomographic acquisition method: ”step and shoot continuous”. The objective of the study is to evaluate planar and tomographic performances of this new collimator and to compare them to GEHC LEHR and to Siemens LEHR. Methods In planar mode, sensitivity and spatial resolution were measured for the three collimators according to NEMA NU1–2000 [1] . In tomographic mode, volumetric sensitivity and spatial resolution were also evaluated according to NEMA NU1–2000. Image quality was measured according NEMA NU2-2012 (contrast of 8) [2] . Projections were acquired according to routine protocols and the volumes were reconstructed thanks to and independent software taking into account spatial resolution depth dependence and attenuation correction. Results Planar mode. Maximum sensitivity was measured for Siemens LEHR (100 cps/MBq), LEHRS’s was 9% lower and GEHC LEHR’s was 22% lower. The full width at half maximum of the linear spread function, at source contact, is equivalent for both LEHR and 5% higher for LEHRS. Nevertheless thanks to Clarity2D, LSF’s FWHM degradation is less important when collimator distance increases. With 15 cm of diffusing material, LEHRS spatial resolution is 9,2 mm, GEHC LEHR is 10,1 mm and Siemens LEHR is 10,6 mm. Tomographic mode. LEHRS volumetric sensitivity is superior to both LEHR’s (16% for Siemens LEHR and 25% for GEHC LEHR). Spatial resolution is equivalent for the 3 collimators. The biggest hot sphere contrast recovery is equivalent for both GEHC collimators (41% for LEHR and 39,3% for LEHRS) and superior to Siemens LEHR (35,7%). LEHRS provides a better background variability (7,9%) than both LEHR (10,1% for GEC and 9,8% for Siemens). Conclusions In planar mode, LEHRS collimator associated to clarity 2D provides higher quality images than the other collimators since then enough diffusing material is placed between the source and the camera. In tomographic mode, the increase of volumetric sensitivity allows to reduce noise in the images (low background variability) while maintaining equivalent or superior contrast recovery and spatial resolution.

Performance evaluation of the next generation solid-state digital photon counting PET/CT system

BackgroundThe first solid-state silicon photomultiplier (SiPM) digital photon counting (DPC) clinical PET/CT system was introduced by Philips in recent years. The system differs from other SiPM-based PET/CT systems and uses lutetiumyttrium oxyorthosilicate (LYSO) scintillators directly coupled with their own individual SiPM DPC detectors eliminating the need for Anger-logic positioning decoding. We evaluated the system performance, characteristics, and stability of the next generation DPC clinical PET/CT based on NEMA NU2-2012 tests, NEMA NU2-2018 test (timing resolution) and human studies.ResultsAn energy resolution of 11.2% was measured. NEMA NU2-2012 tests revealed a spatial resolution (mm in FWHM) from (3.96, 4.01, 4.01) at 1 cm to (5.81, 5.83, 4.95) at 20 cm for (axial, radial, tangential). A 5.7 cps/kBq system sensitivity was measured. Peak noise equivalent count rate (NECR) and peak true count rate could not be determined as each exhibited increasing values up to the maximum activity measured (~ 1100 MBq). The maximum NECR was 171 kcps @ 50.5 kBq/mL, with corresponding scatter fraction of 30.8% and maximum trues of 681 kcps. NEMA hot sphere contrast ranged from 62% (10 mm) to 88% (22 mm), cold sphere contrast of 86% (28 mm) and 89% (37 mm). A timing resolution of 322 ps (22Na point source based) and 332 ps (NEMA NU2-2018) was obtained. It revealed < 1% change in TOF timing and ± 0.4% change in energy resolution during 31-month stability monitoring. CQIE assessment found < 3% axial variance in SUV. 100–60% recovery coefficients of activity concentration at various sphere sizes and contrast levels were measured.ConclusionsThis scanner represents the first solid-state DPC PET/CT, a technologic leap beyond photomultipliers tubes and anger logic. It presents considerable improvements in system performance and characteristics with excellent time-of-flight capability compared to conventional photomultiplier tube (PMT) PET/CT systems. The DPC system leads to promising clinical opportunities with excellent image quality, lesion detectability, and diagnostic confidence.

Assessment of collimators in radium-223 imaging with channelized Hotelling observer: a simulation study.

Radium-223 (223Ra) is used in unsealed radionuclide therapy for metastatic bone tumors. The aim of this study is to apply a computational model observer to 223Ra planar images, and to assess the performance of collimators in 223Ra imaging. The 223Ra planar images were created via an in-house Monte Carlo simulation code using HEXAGON and NAI modules. The phantom was a National Electrical Manufacturers Association body phantom with a hot sphere. The concentration of the background was 55Bq/mL, and the sphere was approximately 1.5-20 times that of the background concentration. The acquisition time was 10min. The photopeaks (and the energy window) were 84 (full width of energy window: 20%), 154 (15%), and 270keV (10%). Each 40 images, with and without hot concentration, were applied to a three-channel difference-of-Gaussian channelized Hotelling observer (CHO), and the signal-to-noise ratio (SNR) of the hot region was calculated. The images were examined using five different collimators: two low-energy general-purpose (LEGP), two medium-energy general-purpose (MEGP), and one high-energy general-purpose (HEGP) collimators. The SNR value was linearly proportional to the contrast of the hot region for all collimators and energy windows. The images of the 84-keV energy window with the MEGP collimator that have thicker septa and larger holes produced the highest SNR value. The SNR values of two LEGP collimators were approximately half of the MEGP collimators. The HEGP collimator was halfway between the MEGP and LEGP. Similar characteristics were observed for other energy windows (154, 270keV). The SNR value of images captured via the 270-keV energy window was larger than 154-keV, although the sensitivity of the 270-keV energy window is lower than 154-keV. The results suggested a positive correlation between the SNR value and the fraction of unscattered photons. The SNR value of CHO reflected the performance of collimators and was available to assess and quantitatively evaluate the collimator performance in 223Ra imaging. The SNR value depends on the magnitudes of unscattered photon count and the fraction of unscattered photon count. Consequently, in this study, MEGP collimators performed better than LEGP and HEGP collimators for 223Ra imaging.

P094] Performance evaluation of point spread function reconstruction algorithm on a new PET-TC TOF scanner

Purpose Aim of this study was to evaluate the performance of PSF reconstruction algorithm of a new PET-TC TOF scanner. Comparison in term of image quality was performed in order to investigate potentialities and differences between PSF algorithm and the standard OSEM algorithm routinely applied in the clinical use. Methods The phantom NEMA 2012 Body Image Quality (18 F, 213 kBq/ml, diameter 10 mm, 13 mm, 17 mm and 22 mm hot spheres (background ratio 4 ÷ 1), diameter 28 mm and 37 mm cold spheres) was acquired with Philips Ingenuity TF PET-TC scanner (TOF, AC-SC). Raw data were reconstructed both with standard OSEM 3D and with PSF, using 20 different paired iteration values (1–500) and regularization levels (1–20). Seven regions of interest (ROIs) were contoured: 4 centered on ”hot” spheres, 2 on ”cold” spheres and 1 on background. Mean value (MV) and standard deviation (SD) of every ROI were calculated: signal to noise ratio (SNR) and contrast to noise ratio (CNR) were compared. Spatial resolution was evaluated as steep of the 10 mm-sphere profile. Results PSF images showed resolution higher (e.g. 3 mm for 30 iterations) than the standard OSEM (6 mm). The more iteration number the higher artifacts presence, especially in the background region. MV and SD values relative to the ”hot spheres” strongly depend on iteration number and regularization level; variations up to +1000% were found (500 iterations and 20 regularization) both on MV and SD values. No variations were noticed on background MV, but SD values increase up to +600%. As consequence SNR and CNR are strongly affected by reconstruction parameters. Conclusions PSF images showed resolution higher than standard OSEM, but also huge artifacts and unacceptable variations in measured activity (and SUV). The use of PSF reconstruction for quantitative purposes is not recommended and its use should be designed for specific uses.

Ignition by moving hot spheres in H2-O2-N2 environments

A combined experimental and numerical study was carried out to investigate thermal ignition by millimeter size (d=6 mm) moving hot spheres in H2-O2-N2 environments over a range of equivalence ratios. The mixtures investigated were diluted with N2 to keep their laminar flame speed constant and comparable to the sphere fall velocity (2.4 m/s) at time of contact with the reactive mixture. The ignition thresholds (and confidence intervals) were found by applying a logistic regression to the data and were observed to increase from lean (Φ=0.39; Tsphere = 963 K) to rich (Φ=1.35; Tsphere = 1007 K) conditions. Experimental temperature fields of the gas surrounding the hot sphere during an ignition event were, for the first time, extracted using interferometry and compared against simulated fields. Numerical predictions of the ignition thresholds were within 2% of the experimental values and captured the experimentally observed increasing trend between lean and rich conditions. The effect of stoichiometry and dilution on the observed variation in ignition threshold was explained using 0-D constant pressure delay time computations.

Fluctuation of quantitative values on acquisition time and the reconstruction conditions in 99mTc-SPECT.

This study aims to carry out a quantitative analysis with high reproducibility using single-photon emission computed tomography/computed tomography (SPECT/CT); we investigated the optimum parameters for the acquisition and the reconstruction. SPECT images were acquired with varying time per view using SPECT phantom (JS-10) and the body phantom of National Electrical Manufacturers Association and International Electrotechnical Commission (Body-phantom), respectively. For the image reconstruction condition, we changed the product of subset and iteration (SI product) and the Gaussian filter using a three-dimensional ordered subset expectation maximization. A combination of no scattering correction and no attenuation correction (SC-/AC-) and a combination of scattering correction and attenuation correction by CT images (SC+/AC+) were performed. The dose linearity, the recovery coefficient, the scatter ratio, and the coefficient of variation were evaluated using JS-10. Using Body-phantom, contrast-to-noise ratios of the hot spheres (13, 17 mm) were calculated. Moreover, the change in the maximum standardized uptake value (SUVmax) and the average SUV (SUVmean) were evaluated for each sphere. From the evaluation results using the JS-10, dose linearity, recovery coefficient, scatter ratio, and coefficient of variation were all good when time per view was 50-150 s, the Gaussian filter was 8-12 mm, and the SI product was 150. From the evaluation results using Body-phantom, comparing the Gaussian filter with 8 mm and 12 mm, the contrast-to-noise ratio was better for 12 mm and the error rate to the change of the scan-time was up to 3.7%. However, SUVmax and SUVmean using 8 mm were closer to the design value of the phantom. It is necessary that Quantitative SPECT be acquired at 50 s or more per view per detection, reconstructed using a three-dimensional ordered subset expectation maximization with SC+/AC+, the SI product is 150 times, and the Gaussian Filter is 8-12 mm. This suggested that the quantitative analysis would be carried out with good reproducibility.

Measurement and Evaluation of Quantitative Performance of PET/CT Images before a Multicenter Clinical Trial

To ensure the reliability of the planned multi-center clinical trial, we assessed the consistence and comparability of the quantitative parameters of the eight PET/CT units that will be used in this trial. PET/CT images were scanned using a PET NEMA image quality phantom (Biodex) on the eight units of Discovery PET/CT 690 from GE Healthcare. The scanning parameters were the same with the ones to be used in the planned trial. The 18F-NaF concentration in the background was 5.3 kBq/ml, while the ones in the spheres of diameter 37 mm, 22 mm, 17 mm and 10 mm were 8:1 as to that of the background and the ones in the spheres of diameter 28 mm and 13 mm were 0 kBq/ml. The consistency of hot sphere recovery coefficient (HRC), cold sphere recovery coefficient (CRC), hot sphere contrast (QH) and cold sphere contrast (Qc) among these 8 PET/CTs was analyzed. The variation of the main quantitative parameters of the eight PET/CT systems was within 10%, which is acceptable for the clinical trial.

Heat transfer at cooling high-temperature bodies in subcooled liquids

In subcooled water film boiling, a particular regime exists featured with very high intensity of heat transfer [3]. The authors’ previous experimental studies confirmed that intensive heat transfer regime occurred in cooling of spheres from copper, nickel and stainless steel at water subcoolings from 25 K under atmospheric pressure. However, this regime was not found during cooling the hot spheres in nonaqueous liquids even at very high subcoolings (up to 170 K). The qualitative analysis of the large domain of the experimental data on heat transfer regimes in cooling high temperature bodies and comparison those with the results on steady film boiling in forced flow of subcooled water lead to the conclusion that the specific regime of highly intensive heat transfer in film boiling of subcooled liquids can exist only in an unsteady process. Basing on this idea, an approximate model of an origination of the intensive heat transfer regime in film boiling was derivate. At rather high liquid subcoolings, random contacts of a liquid wave crests with the protrusions of the wall surface roughness can cause transition to the heat transfer regime of great intensity. Liquid inflow into the region of intensive evaporation at the wetted area boundary (the contact line) is controlled by the capillary pressure gradient. Hydromechanical limit of heat flux density corresponding to the extremely high evaporation rate at this area is proportional to hlgσ/ν. Sharp surface temperature drop in the randomly wetted zone produces unsteady conductive heat flux from a volume of the cooled body. A characteristic time of this unsteady heat flux seems to be determined with a period of wavy flow at the liquid/vapor interface. We assume an analogy of natural convection in a boundary layer of subcooled liquid near a vapor film with gravitational liquid film flow that has been analyzed in the classical Kapitsa study. The model developed explains an effect of thermal effusivity of a cooled sphere metal and influence of coolant properties on occurrence of intensive regime of heat transfer in film boiling. It was shown that for several coolants (FC-72, LN2) this regime is practically unattainable. The calculated values of the surface transient superheats satisfactorily agree with the experimental results on incipience of the intensive heat transfer regime in film boiling of different liquids at the sphere surface from different metals under wide range of subcoolings and pressures.

A note on radiation preheating of some hydrocarbons by combustion products

The aim of this paper is to provide upper bounds of the radiation emitted by hot combustion products, mainly CO2 and H2O, and absorbed by some gaseous cold hydrocarbons, or by cold CO2 and H2O. Line by line calculations with accurate spectroscopic data bases are used to compute the absorbed power under two geometrical configurations: a cold optically thin medium surrounded by spherical hot combustion products, and a thin cold slab in front of a hot combustion parallel slab. The absorbed power and the corresponding characteristic time scale are adjusted by simple and physically based formulas to provide quick estimations for various values of combustion product temperature, pressure, and the radius of the hot sphere or the hot slab thickness. The obtained time scales can be compared in a given application to hydrodynamic or diffusive time scales to decide whether it is necessary to take this preheating phenomenon into account or not.

Influence of magnetic field on Al2O3-H2O nanofluid forced convection heat transfer in a porous lid driven cavity with hot sphere obstacle by means of LBM

In this research, nanofluid flow in a three dimensional porous cavity under the impact of magnetic field is simulated by means of Lattice Boltzmann Method. The enclosure is full of Al2O3-H2O nanofluid. Properties of nanofluid are estimated via single phase model considering Brownian motion effect. Mesoscopic simulations are done for various values of Darcy number, Hartmann number and Reynolds number. Results demonstrate that temperature gradient has direct relationship with Darcy number and Reynolds number. Increasing Lorentz forces leads to reduce in Nusselt number.

Water based nanofluid free convection heat transfer in a three dimensional porous cavity with hot sphere obstacle in existence of Lorenz forces

H2O based nanofluid magnetohydrodynamic free convection in a porous cubic cavity with hot sphere obstacle is investigated by means of Lattice Boltzmann method. Influences of Darcy number (Da), Hartmann number (Ha), and Rayleigh number (Ra) on Al2O3-H2O nanofluid treatment is demonstrated. Thermal conductivity is considered as function of Brownian motion. Results indicate that Lorentz forces makes temperature gradient to decrease. Thermal boundary layer becomes thicker with augment of Hartmann number but opposite treatment is observed for Darcy number.

Time-of-Flight Information Improved the Detectability of Subcentimeter Spheres Using a Clinical PET/CT Scanner.

Recent advancements in clinical PET/CT scanners have improved the detectability of small lesions. However, the ideal reconstruction parameters for detecting small lesions have not yet been sufficiently clarified. The purpose of this study was to investigate the detectability of subcentimeter spheres using a clinical PET/CT scanner. Methods: We used a clinical PET/CT scanner to obtain the data of a National Electrical Manufacturers Association body phantom consisting of 6 small spheres (inner diameters, 4.0, 5.0, 6.2, 7.9, 10, and 37 mm) containing 18F solution. The background activity was 2.65 kBq/mL, and the sphere-to-background ratio was 8. The PET data obtained for 2 and 120 min were reconstructed using ordered-subsets expectation maximization (OSEM), OSEM + point-spread function (PSF), and OSEM + time-of-flight (TOF) with voxel sizes of 2.04 × 2.04 × 2.00 mm (2-mm voxels) and 4.07 × 4.07 × 3.99 mm (4-mm voxels). A gaussian filter was not used. The image quality was evaluated by visual assessment, as well as by physical assessment of the detectability index and recovery coefficients. Results: According to the visual assessment, the detectability of the spheres improved using TOF and a longer acquisition. Using the OSEM+TOF model, the smallest visually detected spheres were 5 mm in diameter with a 120-min acquisition and 6 mm in diameter with a 2-min acquisition. According to physical assessment, the detectability of spheres 10 mm or smaller using the OSEM+TOF image was superior to that using the OSEM image. In addition, the detectability of each hot sphere and recovery coefficient with 2-mm voxels was superior to that with 4-mm voxels. Although OSEM+PSF images showed less background noise, detectability and the recovery coefficient were not improved for spheres 8 mm or smaller. Conclusion: The TOF model with 2-mm voxels improved the detectability of subcentimeter hot spheres on a clinical PET/CT scanner.

Septal penetration correction in I-131 imaging following thyroid cancer treatment

Whole body gamma camera images acquired after I-131 treatment for thyroid cancer can suffer from collimator septal penetration artefacts because of the high energy of the gamma photons. This results in the appearance of ‘spoke’ artefacts, emanating from regions of high activity concentration, caused by the non-isotropic attenuation of the collimator. Deconvolution has the potential to reduce such artefacts, by taking into account the non-Gaussian point-spread-function (PSF) of the system. A Richardson–Lucy deconvolution algorithm, with and without prior scatter-correction was tested as a method of reducing septal penetration in planar gamma camera images. Phantom images (hot spheres within a warm background) were acquired and deconvolution using a measured PSF was applied. The results were evaluated through region-of-interest and line profile analysis to determine the success of artefact reduction and the optimal number of deconvolution iterations and damping parameter (λ). Without scatter-correction, the optimal results were obtained with 15 iterations and λ = 0.01, with the counts in the spokes reduced to 20% of the original value, indicating a substantial decrease in their prominence. When a triple-energy-window scatter-correction was applied prior to deconvolution, the optimal results were obtained with six iterations and λ = 0.02, which reduced the spoke counts to 3% of the original value. The prior application of scatter-correction therefore produced the best results, with a marked change in the appearance of the images. The optimal settings were then applied to six patient datasets, to demonstrate its utility in the clinical setting. In all datasets, spoke artefacts were substantially reduced after the application of scatter-correction and deconvolution, with the mean spoke count being reduced to 10% of the original value. This indicates that deconvolution is a promising technique for septal penetration artefact reduction that could potentially improve the diagnostic accuracy of I-131 imaging.Novelty and significanceThis work has demonstrated that scatter correction combined with deconvolution can be used to substantially reduce the appearance of septal penetration artefacts in I-131 phantom and patient gamma camera planar images, enable improved visualisation of the I-131 distribution. Deconvolution with symmetric PSF has previously been used to reduce artefacts in gamma camera images however this work details the novel use of an asymmetric PSF to remove the angularly dependent septal penetration artefacts.

Experimental and numerical study on moving hot particle ignition

Ignition thresholds for n-hexane-air were experimentally and numerically determined using a moving hot sphere of 6 mm in diameter. The novel experimental setup built for this purpose was described in detail. Two-color pyrometry was used for surface temperature measurements, and shearing interferometry flow field visualization was used to observe the onset of an ignition kernel, and subsequent flame formation and propagation. The probability of ignition was found to be 90% at a sphere surface temperature of 1224 K. Analysis of the interferograms at the ignition threshold indicated that ignition occurs near the region of flow separation. Numerical simulations of the transient development of the 2-D axisymmetric motion and ignition were performed. Four reduced chemical mechanisms, including high and low temperature chemistry, and two diffusion models were used to determine their impact on the numerical prediction of ignition thresholds. The simulation results were unaffected by the choice of diffusion model but were found to be sensitive to the chemical kinetic mechanism used. The predicted ignition threshold temperatures were within 6–12% of the experimentally determined values. The numerical fields of the energy source term and a wall heat flux analysis confirmed the experimental observation that ignition occurs near the region of flow separation at the ignition threshold. Detailed analysis of the species temporal evolution at the ignition location revealed that n-hexane is present in small amounts, demonstrating the importance of accounting for fuel decomposition within the thermal boundary layer when developing simple chemical reaction models.

Modeling the growth of a vapor film formed in contact between a hot metal sphere and water in pressure vessels

The contact between a hot object such as the particles of a molten metal and a cool and relatively volatile fluid such as water likely takes place in metal casting, paper manufacturing industries, and nuclear reactors. The highly intensive and quick heat transfer caused by the contact may increase the pressure in the vapor film formed on a hot particle within a short period leading to the vapor explosion followed by a strong pressure wave in a vessel containing a volatile matter. The present study aims to provide a mathematical model for contacting between a small hot copper metal sphere and water and explain the effect of pressure change in water vessel on the vapor film radius, pressure inside vapor film, as well as the saturation temperature at the interface. In addition, it examines the results of vapor film growth and the internal pressure of the film for such a phenomenon in nuclear power plants with fuel rod coolant pressures ranged between 60 and 150 bar. The results of the extremely high pressures of the vessels indicated an increase in the pressure pulse inside the vapor film within a short period which raised the likelihood of vapor explosion.

Performance evaluation of a novel brain-dedicated SPECT system

Single-photon emission computed tomography (SPECT) imaging is an important diagnostic tool for the early detection of the loss of nigrostriatal dopaminergic neurons in Parkinson’s disease (PD) and similar neurodegenerative disorders. Visualization and quantification of dopamine transporter (DAT) binding in the striatum is an established diagnostic tool to detect nigrostriatal dopaminergic degeneration. Given the small size of the striatum, high-resolution imaging is recommended. The InSPira HD system, a novel brain-dedicated SPECT scanner, allows for such detailed information with a spatial resolution down to ~ 3 mm full width at half maximum (FWHM). The current study examines performance of the InSPira HD for DAT imaging, by combining phantom tests from NU 1-2012 and NU 2-2012, and striatal scans. Due to the unique geometry of the InSPira, and fixed acquisition and reconstruction settings, standard National Electrical Manufacturers Association (NEMA) testing is not applicable. Therefore, a combination of NU 1-2012 and NU 2-2012 standards were applied, with modifications to accommodate the InSPira HD. A small Jaszczak phantom with hot spheres and cold rod inserts was used to determine recovery coefficients, contrast, and uniformity. Spatial resolution was evaluated across the field of view (FOV) for point and line sources in air and water. A striatal phantom was used to model DAT imaging. A clinical, a high-resolution, and an experimental research reconstruction method were compared. Acquired SPECT images demonstrated spatial resolution in air of ~ 3 mm in the center in the FOV for the high-resolution reconstruction approach. Spatial resolution in air for the clinical and research reconstruction approach was ~ 6–8 mm in the center of the FOV, which decreased in the transaxial plane with increasing radial distance from the center of the FOV. Reconstructed images of the uniform area of the Jaszczak phantom showed limited variability with a coefficient of variation of 2.6% for the clinical reconstruction and 3.0% for the research reconstruction. The ≥ 6-mm rod group and all spheres were resolved for the clinical and research reconstruction approaches. Recovery coefficients (RCs) for the Jaszczak phantom ranged from 0.49 to 0.89 (sphere diameters between 9.8 and 31.2 mm). RCs for the striatal phantom ranged from 0.50 to 0.55, with linearity of striatal ratios for a range of background concentrations (R = 0.97). Results from the phantom data demonstrated acceptable image quality for the InSPira HD system for DAT SPECT imaging in humans.

Quantitative analysis of phantom studies of 111In and 68Ga imaging of neuroendocrine tumours

BackgroundNuclear medicine imaging of neuroendocrine tumours is performed either by SPECT/CT imaging, using 111In-octreotide or by PET/CT imaging using 68Ga-radiolabelled somatostatin analogs. These imaging techniques will give different image quality and different detection thresholds for tumours, depending on size and activity uptake. The aim was to evaluate the image quality for 111In-SPECT and 68Ga-PET imaging, i.e. the smallest volume possible to visualize for different source-to-background activity ratios. The accuracy of quantification of lesion volume and activity was also investigated to develop an objective evaluation for radionuclide therapy eligibility.The phantom study was performed using the NEMA IEC Body Phantom with six hot spheres having inner diameters of 10, 13, 17, 22, 28, and 37 mm, filled with either 68Ga or 111In with sphere-to-background ratios (SBRs) of no background activity, 5:1, 2.5:1, and 1.25:1. Activity ratios of 1.25:1 and 2.5:1 are clinically found for lesions close to the liver and spleen. Clinical acquisition and reconstruction protocols were applied. Line profiles were drawn to evaluate the smallest detectable volume within a given SBR. Recovery curves based on threshold-based VOIs, threshold-based VOIs adapted to the background and CT-based ROIs were obtained for all SBRs and sphere diameters, allowing for quantification.ResultsThe 10-mm sphere was not possible to detect in SPECT images. It was detectable in PET images for SBRs of 2.5:1 and higher. In a background corresponding to the activity uptake in the liver, spheres larger than 22–37 mm were detectable in the 111In-SPECT images and spheres larger than 13–22 mm were detectable in the 68Ga-PET images. The maximum activity concentration was accurately quantified for spheres larger than 22 mm in the PET images; however, the quantification was impaired by sphere size and background activity.ConclusionsIt was not possible to detect the 10-mm sphere in any of the SPECT images. In a background corresponding to the activity uptake in the liver, spheres larger than approximately 30 mm were visible in the 111In-SPECT images and spheres larger than approximately 17 mm were visible in the 68Ga-PET images. Sphere diameter and background activity strongly affect the possibility of a correct quantification.

Thermoelectric properties of hot pressed CZTS micro spheres synthesized by microwave method

ABSTRACTMicrowave synthesis of Copper Zinc Tin Sulphide (CZTS) sphere like particles has been demonstrated. The structural and morphological properties of CZTS particles are characterized by XRD, SEM and Raman spectroscopy and subsequently thermoelectric properties are investigated. XRD results of prepared powder sample matches well with tetragonal crystal structure of CZTS bulk. No other impurity phase has been detected from the XRD analysis. Raman spectrum further confirms the formation of single phase CZTS with characteristics peak for CZTS at 334.1 cm-1. SEM studies reveal that the CZTS particles are spherical in shape with uniform sizes of ∼ 250-350 nm. Hot pressed CZTS system shows a power factor ∼21 µW/mK2 and ZT∼ 0.024 at 623 K. Significant enhancement in the Figure of merit for CZTS system is observed in comparison to reported nanostructures of the same system may be due to increased electrical conductivity.

Use of count-based image reconstruction to evaluate the variability and repeatability of measured standardised uptake values.

Standardized uptake values (SUVs) are the most widely used quantitative imaging biomarkers in PET. It is important to evaluate the variability and repeatability of measured SUVs. Phantom studies seem to be essential for this purpose; however, repetitive phantom scanning is not recommended due to the decay of radioactivity. In this study, we performed count-based image reconstruction to avoid the influence of decay using two different PET/CT scanners. By adjusting the ratio of 18F-fluorodeoxyglucose solution to tap water, a NEMA IEC body phantom was set for SUVs of 4.0 inside six hot spheres. The PET data were obtained using two scanners (Aquiduo and Celesteion; Toshiba Medical Systems, Tochigi, Japan). We set the start time for image reconstruction when the total radioactivity in the phantom was 2.53 kBq/cc, and employed the counts of the first 2-min acquisition as the standard. To maintain the number of counts for each image, we set the acquisition time for image reconstruction depending on the decay of radioactivity. We obtained 50 images, and calculated the SUVmax and SUVpeak of all six spheres in each image. The average values of the SUVmax were used to calculate the recovery coefficients to compare those measured by the two different scanners. Bland-Altman analyses of the SUVs measured by the two scanners were also performed. The measured SUVs using the two scanners exhibited a 10–30% difference, and the standard deviation (SD) of the measured SUVs was between 0.1–0.2. The Celesteion always exhibited higher values than the Aquiduo. The smaller sphere exhibited a larger SD, and the SUVpeak had a smaller SD than the SUVmax. The Bland-Altman analyses showed poor agreement between the SUVs measured by the two scanners. The recovery coefficient curves obtained from the two scanners were considerably different. The Celesteion exhibited higher recovery coefficients than the Aquiduo, especially at approximately 20-mm-diameter. Additionally, the curves were lower than those calculated from the standard 30-min acquisition images. We propound count-based image reconstruction to evaluate the variability and repeatability of measured SUVs. These results are also applicable for the standardization and harmonization of SUVs in multi-institutional studies.

Characterization and simulation of noise in PET images reconstructed with OSEM: Development of a method for the generation of synthetic images

IntroductionThe goals of the study are to characterize imaging properties in 2D PET images reconstructed with the iterative algorithm Ordered-Subset Expectation Maximization (OSEM) and to propose a new method for the generation of synthetic images. Material and methodsThe noise is analyzed in terms of its magnitude, spatial correlation, and spectral distribution through standard deviation, Autocorrelation Function, and Noise Power Spectrum (NPS), respectively. Their variations with position and activity level are also analyzed. This noise analysis is based on phantom images acquired from 18F uniform distributions. Experimental Recovery Coefficients of hot spheres in different backgrounds are employed to study the spatial resolution of the system through Point Spread Function (PSF). The NPS and PSF functions provide the baseline for the proposed simulation method: convolution with PSF as kernel and noise addition from NPS. ResultsThe noise spectral analysis shows that the main contribution is of random nature. It is also proven that attenuation correction does not alter noise texture but it modifies its magnitude. Finally, synthetic images of two phantoms, one of them an anatomical brain, are quantitatively compared with experimental images showing a good agreement in terms of pixel values and pixel correlations. Thus, the Contrast to Noise Ratio for the biggest sphere in the NEMA IEC phantom is 10.7 for the synthetic image and 8.8 for the experimental image. ConclusionsThe properties of the analyzed OSEM-PET images can be described by NPS and PSF functions. Synthetic images, even anatomical ones, are successfully generated by the proposed method based on the NPS and PSF.