8,876 research outputs found
Validation of 99 m Tc and 177 Lu quantification parameters for a Monte Carlo modelled gamma camera
No full textAbstract Purpose Monte Carlo (MC) simulation in Nuclear Medicine is a powerful tool for modeling many physical phenomena which are difficult to track or measure directly. MC simulation in SPECT/CT imaging is particularly suitable for optimizing the quantification of activity in a patient, and, consequently, the absorbed dose to each organ. To do so, validating MC results with real data acquired with gamma camera is mandatory. The aim of this study was the validation of the calibration factor (CF) and the recovery coefficient (RC) obtained with SIMIND Monte Carlo code for modeling a Siemens Symbia Intevo Excel SPECT-CT gamma camera to ensure optimal 99 m Tc and 177 Lu SPECT quantification. Methods Phantom experiments using 99 m Tc and 177 Lu have been performed to measure spatial resolution and sensitivity, as well as to evaluate the CF and RC from acquired data. The geometries used for 2D planar imaging were (1) Petri dish and (2) capillary source while for 3D volumetric imaging were (3) a uniform filled cylinder phantom and (4) a Jaszczack phantom with spheres of different volumes. The experimental results have been compared with the results obtained from Monte Carlo simulations performed in the same geometries. Results Comparison shows good accordance between simulated and experimental data. The measured planar spatial resolution was 8.3 ± 0.8 mm for 99 m Tc and 11.8±0.6 mm for 177 Lu. The corresponding data obtained by SIMIND for 99 m Tc was 7.8±0.1 mm, while for 177 Lu was 12.4±0.4 mm. The CF was 110.1±5.5 cps/MBq for Technetium and 18.3±1.0 cps/MBq for Lutetium. The corresponding CF obtained by SIMIND for 99 m Tc was 107.3±0.3 cps/MBq, while for 177 Lu 20.4±0.7 cps/MBq. Moreover, a complete curve RCs vs Volume (ml) both for Technetium and Lutetium was determined to correct the PVE for all volumes of clinical interest. In none of the cases, a RC coefficient equal to 100 was found. Conclusions The validation of quantification parameters shows that SIMIND can be used for simulating both gamma camera planar and SPECT images of Siemens Symbia Intevo using 99 m Tc and 177 Lu radionuclides for different medical purposes and treatments
Comparison of the averaged biodistribution and pharmacokinetics between [99mTc]Tc-HYNIC-TOC and [177Lu]Lu-DOTA-TATE in neuroendocrine tumor patients
Full text linkBACKGROUND: Accurate pre-therapeutic dosimetry can potentially help optimize peptide receptor radionuclide therapy in patients with neuroendocrine tumors. While positron emission tomography (PET) imaging with [68Ga]Ga-DOTA-peptides has been previously studied for predicting therapeutic absorbed dose, it is limited by its single-time-point nature. In contrast, [99mTc]Tc-HYNIC-TOC offers advantages such as lower cost and multi-time-point imaging capability, but its potential to predict [177Lu]Lu-DOTA-TATE biodistribution remains underexplored. The study objective was to evaluate pharmacokinetics, isolating biological clearance from physical decay effects, and compare relative organ uptake ratios between the compounds. This work lays the foundation for future studies exploring [99mTc]Tc-HYNIC-TOC as a predictive tool for treatment planning — particularly in regions where [68Ga] Ga-DOTA-peptides are less accessible. MATERIAL AND METHODS: The study compared the biodistribution and pharmacokinetics of [99mTc]Tc-HYNIC-TOC and [177Lu]Lu-DOTA-TATE in neuroendocrine tumor (NET) patients by modeling pharmacokinetics, analyzing time-integrated activity coefficients, and biological half-lives in the kidneys, liver, spleen, and lesions from 11 diagnostic and 8 therapeutic studies. RESULTS: [177Lu]Lu-DOTA-TATE showed significantly higher kidney-to-spleen and lesion-to-spleen uptake ratios compared to [99mTc]Tc-HYNIC-TOC, indicating greater relative accumulation in these organs. There was no statistically significant difference in liver-to-spleen uptake between the two compounds. The biological half-life in the kidneys was longer for [99mTc]Tc-HYNIC-TOC than for [177Lu]Lu-DOTA-TATE, suggesting faster renal clearance of the therapeutic agent. Liver and spleen kinetics were comparable between the two tracers. CONCLUSIONS: While [99mTc]Tc-HYNIC-TOC and [177Lu]Lu-DOTA-TATE show similar biodistribution patterns in the liver and spleen, they differ in renal and lesion uptake and clearance kinetics. The ability of [99mTc]Tc-HYNIC-TOC to capture dynamic behavior through multi-time-point imaging may offer improved prediction of [177Lu]Lu-DOTA-TATE absorbed dose
Lu
Full text linkBACKGROUND: Single photon emission computed tomography (SPECT) is an imaging modality that has demonstrated its utility in a number of clinical indications. Despite this progress, a high sensitivity, high spatial resolution, multi-tracer SPECT with a large field of view suitable for whole-body imaging of a broad range of radiotracers for theranostics is not available.
PURPOSE: With the goal of filling this technological gap, we have designed a cadmium zinc telluride (CZT) full-ring SPECT scanner instrumented with a broad-energy tungsten collimator. The final purpose is to provide a multi-tracer solution for brain and whole-body imaging. Our static SPECT does not rely on the dual- and the triple-head rotational SPECT standard paradigm, enabling a larger effective area in each scan to increase the sensitivity. We provide a demonstration of the performance of our design using a realistic model of our detector with simulated body-sized phantoms filled with 99m Tc and 177 Lu.
METHODS: We create a realistic model of our detector by using a combination of a Geant4 Application for Tomographic Emission (GATE) Monte Carlo simulation and a finite element model for the CZT response, accounting for low-energy tail effects in CZT that affects the sensitivity and the scatter correction. We implement a modified dual-energy-window scatter correction adapted for CZT. Other corrections for attenuation, detector and collimator response, and detector gaps and edges are also included. The images are reconstructed using the maximum-likelihood expectation-maximization. Detector and reconstruction performance are characterized with point sources, Derenzo phantoms, and a body-sized National Electrical Manufacturers Association (NEMA) Image Quality (IQ) phantom for both 99m Tc and 177 Lu.
RESULTS: Our SPECT design can resolve 7.9 mm rods for 99m Tc (140 keV) and 9.5 mm for 177 Lu (208 keV) in a hot-rod Derenzo phantom with a 3-min exposure and reach an image contrast of 78% for 99m Tc and 57% for 177 Lu using the NEMA IQ phantom with a 6-min exposure. Our modified scatter correction shows an improved contrast-recovery ratio compared to a standard correction.
CONCLUSIONS: In this paper, we demonstrate the good performance of our design for whole-body imaging purposes. This adds to our previous demonstration of improved qualitative and quantitative 99m Tc imaging of brain perfusion and 123 I imaging of dopamine transport with respect to state-of-the-art NaI dual-head cameras. We show that our design provides similar IQ and contrast to the commercial full-ring SPECT VERITON for 99m Tc. Regarding 177 Lu imaging of the 208 keV emissions, our design provides similar contrast to that of other state-of-the-art SPECTs with a significant reduction in exposure. The high sensitivity and extended energy range up to 250 keV makes our SPECT design a promising alternative for clinical imaging and theranostics of emerging radionuclides
PROPERTIES OF GRANULAR HIGH-TC SUPERCONDUCTORS IN AN EFFECTIVE MEDIUM THEORY
No full textThe authors consider the transport, electromagnetic and thermodynamic properties of a granular high-Tc superconductor by constructing a model of weakly coupled (Josephson junctions) superconducting and normal grains. They start by using an effective medium theory (EMT), for the conductivity and susceptibility, which is supplemented by London electrodynamics for the superconducting grains, in the limit of weak magnetic field and zero transport current. Next the authors assume a Gaussian distribution of junction resistances R, with mean Ro and variance sigma , which determines the Josephson coupling energy between grains. The criterion that this energy must be greater than kT for superconducting clusters enables them to determine the superconducting fraction cs as a function of temperature. With this they complete the determination of the conductivity and susceptibility of their model. The authors also discuss the specific heat, neglecting fluctuations, which is directly proportional to cs, in their approximation. Throughout this paper, they adopt the Ginzburg-Landau (GL) expressions for the energy gap Delta (order parameter), which is valid near Tc and for the specific heat CH, but they allow for possible deviations of numerical coefficients in these expressions from the Bardeen, Cooper and Schrieffer (BCS) microscopic theory, by introducing phenomenological parameters. The authors find, in accord with experiments, differences between the temperatures of zero resistivity, of resistivity drop and for maximum Meissner effect
Delayed orbital emphysema as the manifestation of isolated medial orbital wall fracture.
No full text
Overexpression of neuronal intermediate filament protein alpha-internexin in PC12 cells.
No full textMechanisms for accumulation and migration of technetium-99 in saltmarsh sediments
No full textThis thesis describes the development of analytical methods for both the bulk determination of 99Tc, and determination of 99Tc in sequential extracts from sediments. These methods have been used to collect data, which, along with trace and major element data have been used to interpret the mechanisms for 99Tc input, migration and accumulation in saltmarshes. The inventory of 99Tc stored in the Thornflatt Saltmarsh, Esk Estuary has also been determined. The routine determination of 99Tc in bulk samples uses 99mTc as a yield monitor. Samples are ignited stepwise to 550°C and the 99Tc is extracted using 8M nitric acid. Many contaminants are precipitated with Fe(OH)3 and the Tc in the supernant is pre-concentrated and further purified using anion-exchange chromatography. Final separation of Tc from Ru is achieved by extraction of Tc into 5% TnOA in xylene from 2M sulphuric acid. The yield is determined by γ-spectrometric analysis of 99mTc. Determination of 99Tc is made by liquid scintillation counting. Typical recoveries are in the order of 70-95% and the method has a detection limit of 1.7 Bq/kg for a sample size of 10g. Determination of Tc in sequential extracts uses operationally defined procedures to extract: exchangeable Tc, reducible Tc and oxidisable Tc. An initial water wash is used to extract any occluded Tc and a final leach in 8 M nitric acid is used to dissolve any residual Tc. The isolation of 99Tc uses TEVA resin for Extracts 1-4 and the decontamination procedure developed for bulk analysis for Extract 5. 99mTc was used as a yield monitor, and determination of 99Tc is by liquid scintillation counting. Limits of detection were dependent on the amount of 99mTc tracer used but were found to be as low as 2.4 Bq/kg for a sample size of 2g. A study was made of the mechanisms responsible for the accumulation and migration of Tc in estuarine sediments using sediments collected from saltmarshes at Thornflatt, Carlaverock and the Ribble Estuary. 99Tc was present at determinable activities in all the sediment cores taken from these sites. Good correlations between Tc and CaO as well as CO3 concentrations and poor correlation between Tc and radionuclides adsorbed to inorganic detritus infer a direct input of 99Tc to marsh sediments. Determination of 99Tc in biota living on the marsh also showed that this was not a significant pathway for input of Tc to the sediments. Sequential extraction data imply sorption to an organic fraction of the sediment. Stable element and sequential extraction data indicates that Tc is readily oxidised and remobilised before reprecipitation where redox conditions are favourable. Data indicate a reduction potential between those of the MnIV to MnII reaction and the FeIII to FeII reaction is necessary for re-accumulation to occur, as suggested by published thermodynamic data. Data collected from reducing sediments imply that similar mechanisms are responsible for the accumulation of Mn (e.g. reduction by sulphate reducing bacteria) and the accumulation of Tc. The inventory of 99Tc held within the Thornflatt saltmarsh is proportionally less than that of 137Cs or 241Am when compared to discharges from Sellafield. However a higher proportion of 99Tc is transferred from Seliafield and incorporated into saltmarsh sediments than is suggested by previously published standard distribution coefficient data. Saltmarsh sediments are therefore a more important sink of 99Tc than extrapolations made from inventories of other radionuclides would suggest
Service-oriented models for audiovisual content storage
No full textWhat are the important topics to understand if involved with storage services to hold digital audiovisual content? This report takes a look at how content is created and moves into and out of storage; the storage service value networks and architectures found now and expected in the future; what sort of data transfer is expected to and from an audiovisual archive; what transfer protocols to use; and a summary of security and interface issues
- …
