Uniform Activity Distribution Research Articles

Developmental dynamics of mitochondrial fission and fusion proteins in functionally divergent skeletal muscles of goat.

During skeletal muscle development, the intricate mitochondrial network formation relies on continuous fission and fusion. This process in larger mammals differs from rodents, the most used animal models. However, the expression pattern of proteins regulating mitochondrial dynamics in developing skeletal muscle remains unexplored in larger mammals. Therefore, we characterized the cellular expression and tissue-level distribution of these proteins during development taking goat as a model. We have performed histological and immunohistochemical analyses to study metabolic features in various muscles. Neonatal muscles display uniform distribution of mitochondrial activity. In contrast, adult muscles exhibit clear distinctions based on their function, whether dedicated for posture maintenance or facilitating locomotion. Mitochondrial fission proteins like DRP-1, MFF, and fusion proteins like MFN-1 and 2 are abundantly expressed in neonatal muscles. Fission proteins exhibit drastic downregulation with limited peripheral expression, whereas fusion proteins continue to express in a fiber-specific manner during adulthood. Locomotory muscles exhibit different fibers based on mitochondrial activity and peripheralization with high SDH activity. The proximity ligation assay between MFN1 and MFN2 demonstrates that their interaction is restricted to subsarcolemmal mitochondria in adult fibers while distributed evenly in neonatal fibers. These differences between postural and locomotory muscles suggest their physiological and metabolic properties are different.

Characterization and impact of dissolved gases in a high-frequency flow reactor

Addressing the growing demands for sustainable green technology in chemical processes, we aim to develop a novel high-frequency ultrasonic flow reactor that utilizes converting ultrasound waves, resulting in intense localized acoustic pressure fields. Our hypothesis that our design of converging waves will establish a uniform spatial distribution of cavitation activity with high energy density, thereby augmenting the rate of radical formation and significantly enhancing overall reactor performance. To validate the hypothesis, KI and terephthalic acid dosimetry were performed. A comprehensive calorimetric study was employed for acoustic power, yielding valuable insight into the energy dynamics of the system. Furthermore, our research systematically assesses the impact of dissolved gases and varying flow rates on reactor performance. Notably, we observe that dissolved gases in the reaction medium exert a substantial influence on reactor efficiency. Additionally, an increased flow rate beyond the optimum decelerates hydroxyl radical generation due to a lower residence time. The detailed characterization, facilitated by dosimetry techniques, unveils the potential of the sonochemical reactor for industrial applications.

Self-mixing in microtubule-kinesin active fluid from nonuniform to uniform distribution of activity

Active fluids have applications in micromixing, but little is known about the mixing kinematics of systems with spatiotemporally-varying activity. To investigate, UV-activated caged ATP is used to activate controlled regions of microtubule-kinesin active fluid and the mixing process is observed with fluorescent tracers and molecular dyes. At low Péclet numbers (diffusive transport), the active-inactive interface progresses toward the inactive area in a diffusion-like manner that is described by a simple model combining diffusion with Michaelis-Menten kinetics. At high Péclet numbers (convective transport), the active-inactive interface progresses in a superdiffusion-like manner that is qualitatively captured by an active-fluid hydrodynamic model coupled to ATP transport. Results show that active fluid mixing involves complex coupling between distribution of active stress and active transport of ATP and reduces mixing time for suspended components with decreased impact of initial component distribution. This work will inform application of active fluids to promote micromixing in microfluidic devices.

A Realistic Multiregion Mouse Kidney Dosimetry Model to Support the Preclinical Evaluation of Potential Nephrotoxicity of Radiopharmaceutical Therapy.

Suborgan absorbed dose estimates in mouse kidneys are crucial to support preclinical nephrotoxicity analyses of α- and β-particle-emitting radioligands exhibiting a heterogeneous activity distribution in the kidneys. This is, however, limited by the scarcity of reference dose factors (S values) available in the literature for specific mouse kidney tissues. Methods: A computational multiregion model of a mouse kidney based on high-resolution MRI data from a healthy mouse kidney was developed. The model was used to calculate S values for 5 kidney tissues (cortex, outer and inner stripes of outer medulla, inner medulla, and papilla and pelvis) for a wide range of β- or α-emitting radionuclides (45 in total) of interest for radiopharmaceutical therapy, using Monte Carlo calculations. Additionally, regional S values were applied for a 131I-labeled single-domain antibody fragment with predominant retention in the outer stripe of the renal outer medulla. Results: The heterogeneous activity distribution in kidneys of considered α- and low- to medium-energy β-emitters considerably affected the absorbed dose estimation in specific suborgan regions. The suborgan tissue doses resulting from the nonuniform distribution of the 131I-labeled antibody fragment largely deviated (from -40% to 57%) from the mean kidney dose resulting from an assumed uniform activity distribution throughout the whole kidney. The absorbed dose in the renal outer stripe was about 2.0 times higher than in the cortex and in the inner stripe and about 2.6 times higher than in inner tissues. Conclusion: The use of kidney regional S values allows a more realistic estimation of the absorbed dose in different renal tissues from therapeutic radioligands with a heterogeneous uptake in the kidneys. This constitutes an improvement from the simplistic (less accurate) renal dose estimates assuming a uniform distribution of activity throughout kidney tissues. Such improvement in dosimetry is expected to support preclinical studies essential for a better understanding of nephrotoxicity in humans. The dosimetric database has added value in the development of new molecular vectors for radiopharmaceutical therapy.

Abstract No. 194 Tumor response after ablative Y-90 transarterial radioembolization for hepatocellular carcinoma based on post-hoc voxel-based dosimetry

Dosimetry for glass trans-arterial radioembolization (TARE) is commonly calculated via a uniform activity distribution model. Recent studies have demonstrated improved tumor response with increased dose to perfused area though no tumor dose threshold is established. This study evaluates dose to tumor and treatment response (mRECIST and LI-RADS criteria) after TARE for early-stage hepatocellular carcinoma (HCC) to determine a threshold tumor dose to predict a complete imaging response.

Biokinetic model for the calculation of dose coefficients for oral and intravenous administration of 14C labeled drugs

Abstract A first order biokinetic model is presented for the calculation of dose coefficients from human activity excretion data after intravenous and oral administration of 14C labeled drugs. It is intended for the dose estimation in human studies in drug research, where the number of measurements is low and their uncertainty rather high. The model depends on only 6 parameters that are to be adjusted with the help of the measurement data. A comparison of measured and calculated activities in excreta of four human studies on 14C labeled drugs revealed considerable agreement, although some limitations have to be accepted. In contrast to the biokinetic model for 14C in organic compounds recommended by the International Commission on Radiological Protection (ICRP) the present model does not assume a fixed biological half-life of 40 days, but follows the experimental data. In consequence, the resulting dose coefficients differ from the ICRP value. For experimental data tested and assuming uniform activity distribution, the committed effective doses amount between one twenty-fifth to one fiftieth of the values calculated from the ICRP model. The uncertainty of the derived dose coefficients is estimated to be about ± 50%.

A METHOD TO IDENTIFY AND LOCALIZE A SINGLE HOT PARTICLE IN THE LUNGS USING AN ARRAY OF HIGH-PURITY GERMANIUM DETECTORS FOR IMPROVED ESTIMATE OF THE DEPOSITED ACTIVITY.

A new method has been developed to identify and localize a single hot particle in the lungs using an array of four high-purity germanium detectors. The method is based upon calculating a set of three count rate ratios (generated by each individual detector in the array) that are evaluated in sequence to designate whether the measured deposition can be associated with a hot particle rather than the default assumption of a uniform activity distribution. Identification and localization of the hot particle are determined from a single in vivo measurement in which detectors are positioned above and below the thorax. The method was tested using an anthropomorphic thorax phantom in which point sources of 241Am, 137Cs and 60Co were individually inserted in the lungs at 15 different locations and were measured using a scanning bed whole-body counter. Depending upon source location and photon energy, a bias of -35% up to +76% could be introduced by falsely assuming a uniform activity distribution in the lungs. This bias would directly translate to an erroneous dose estimate to the lungs. It was demonstrated that by using the appropriate detector efficiencies for the single hot particle, the bias associated with the activity determination is reduced to <10% and~2% in average.

Extension of the potential intervals of high redox activity and electronic conductivity of polypyrrole films on electrode surface via their electrochemical multi-cycle treatment in monomer-free solution

Thin polypyrrole films (thickness: about 30 nm) have been deposited at electrode surface via potentiostatic oxidation of dilute (1 mM) pyrrole solution in acetonitrile (AN). It has been shown that their subsequent treatment by means of multi-cycle voltammetry within a broad potential range (up to -2.0 V vs. Ag/Ag+ in AN) leads to their "activation", i.e. to a very strong extension of their redox response region in the negative direction as well as to almost uniform distribution of the redox activity within this potential range. Region of their high conductivity under in situ conditions has also extended significantly. Spectral and electrocatalytic properties of such PPy films before and after their "activation" have been analyzed. Two parameters for characterization of the variation of film's properties in the course of its "activation" (redox efficiency of polymerization and width of electroactivity region) have been proposed. Comparison of films deposited at different potentials (from 0.6 V to 0.8 V) has revealed that the effect of their "activation" increases for lower polymerization potential. Films deposited at 0.6 V possess after their "activation" a very broad electroactivity range (almost 2.5 V) and a record high redox charge per monomer unit (its oxidation degree) inside the film in contact with AN solution, 0.45. Such unusual properties of "activated" PPy films make them prospective materials for various applications.

Preclinical dosimetric studies of 177 Lu-scFvD2B and comparison with 177 Lu-PSMA-617 and 177 Lu-iPSMA endoradiotherapeutic agents.

Internal dosimetry has become a very important tool to evaluate the risks and benefits of new endoradiotherapeutic agents. Nowadays, some of the most successful targeted radionuclide therapy (TRT) agents are 177 Lu-DOTA conjugates based on low molecular weight (LMW) Glu-ureido PSMA inhibitors. It has, however, been demonstrated that the DOTA chelating moiety reduces the internalization of the LMW-PSMA agent and its radiation dose to the tumor. Previously, we reported that 177 Lu-scFvD2B, an antibody-based construct, demonstrated statistically significant higher cell uptake and internalization in LNCaP prostate cancer (PCa) cells (PSMA-positive) when compared to the LMW-PSMA agents, 177 Lu-PSMA-617 and 177 Lu-iPSMA, two of the endoradiotherapeutic agents which currently are the most used in PCa therapy. The aim of this study is to estimate the preclinical 177 Lu-scFvD2B organ and tumor-absorbed doses, and to compare the values with those of 177 Lu-PSMA-617 and 177 Lu-iPSMA. 177 Lu-scFvD2B, 177 Lu-PSMA-617, and 177 Lu-iPSMA were prepared and their radiochemical purity determined. Biodistribution studies of each radiopharmaceutical were then carried out in healthy mice to define the main source organs (SO) and to calculate the number of disintegrations in each source organs per unit of administered activity (NSO ). Absorbed dose in the main organs were then calculated for each 177 Lu-conjugate by means of OLINDA/EXM 2.1.1 software, using the calculated NSO for both the adult male and the mouse phantoms as program inputs. Images of mice bearing micropulmonary tumors injected with 177 Lu-conjugates were also obtained. Tumor standardized uptake values (SUV) for the different conjugates, obtained from the 3D SPECT image reconstruction of these mice, were used as the number of disintegrations in a tumor site per unit of administered activity (NT ). The tumor-absorbed dose was calculated using the published electron dose S-values for sphere models with diameters ranging from 10µm to 10mm and considering a uniform activity distribution and tumor density equivalent to water density. All 177 Lu-labeled agents were obtained in high yield (98%). Dosimetric studies carried out using mouse phantoms demonstrated that organ absorbed doses of 177 Lu-scFvD2B were from 1.4 to 2.3 times higher than those for 177 Lu-iPSMA and from 1.5 to 2.6 times higher than those for 177 Lu-PSMA-617. However, the 177 Lu-scFvD2B values of tumor-absorbed doses for all investigated tumor sizes were from 2.8 to 3.0 times greater than those calculated for 177 Lu-iPSMA and 177 Lu-PSMA-617, respectively. Moreover, 177 Lu-scFvD2B showed the highest tumor/kidney ratio when compared to those reported for 177 Lu-albumin conjugates. In this preclinical study, we demonstrated the potential of 177 Lu-scFvD2B as a therapeutic agent for PSMA-expressing tumors, due to its higher tumor-absorbed dose when compared with 177 Lu-LMW agents.

АНТИГРАВИТАЦИОННЫЕ СВОЙСТВА ВОДНОЙ СРЕДЫ И ИХ ИСПОЛЬЗОВАНИЕ ДЛЯ ГИДРОКОРЕКЦИИ ДВИГАТЕЛЬНЫХ НАРУШЕНИЙ У ДЕТЕЙ

The article considers the unique physical properties of the water environment and their positive impact to the psychophysical development of the child. The most important therapeutic and healing effect of water is described comprehensively – its anti-gravity effect on the musculoskeletal system of a human. The mechanism of the Archimedean (buoyant) force action is presented, the counteraction of which largely compensates the component of the compression gravityeffect. As a result, the overall load on the skeleton and muscle system of the child is reduced. It has fundamental correcting importance of the physical development of children with musculoskeletal systemdisorders. All the correction vectors of this general anti-gravity effect are analyzed in detail, which include: work with weakened children; wards with a delay in motor and/or psychomotor development; having hypotonic status of the muscles of the body and limbs; prevention and correction of posture disorders of children in all planes; height risestimulation of the child body; the effect of the uniform distribution of physical activity of the childmusculoskeletal system; an amplitude increase of the limbs and the jointsmovements; smooth stimulation of the supporting ability development of the feet and lower limbs; adequate stimulation of the walking function formation in lightened hydrostatic weightlessnessconditions. In the formulated conclusions, the presence of unique physical properties of water in the development, correction and recovery stimulationof children with disabilities is noted. Specific correction vectors are proposed, according to which it is possible successfully to use the general antigravity effect of water in physical educationof children with musculoskeletal systemdisorders. Prospects for further research of this scientific and practical direction of hydrocorrection are outlined, which consist of studying its capabilities in relation to children of preschool and primary school age with different types of musculoskeletal system disorders in etiology and pathogenesis. Key words: anti-gravity effect, water environment, swimming, hydrocorrection, children with musculoskeletal systemdisorders.

Simulation of the effect of mucociliary clearance on the bronchial distribution of inhaled radon progenies and related cellular damage using a new deposition and clearance model for the lung

Most of the current dosimetry models of inhaled short-lived radon decay products assume uniform activity distributions along the bronchial airways. In reality, however, both deposition and clearance patterns of inhaled radon progenies are highly inhomogeneous. Consequently, a new deposition-clearance model has been developed that accounts for such inhomogeneities and applied together with biophysical models of cell death and cell transformation. The scope of this study was to apply this model which is based on computational fluid and particle dynamics methods, in an effort to reveal the effect of mucociliary clearance on the bronchial distribution of deposited radon progenies. Furthermore, the influence of mucociliary clearance on the spatial distribution of biological damage due to alpha-decay of the deposited radon progenies was also studied. The results obtained demonstrate that both deposition and clearance of inhaled radon progenies are highly non-uniform within a human airway bifurcation unit. Due to the topology of the carinal ridge, a slow clearance zone emerged in this region, which is the location where most of the radio-aerosols deposit. In spite of the slow mucus movement in this zone, the initial degree of inhomogeneity of the activity due to the nonuniform deposition decreased by a factor of about 3 by considering the effect of mucociliary clearance. In the peak of the airway bifurcation, the computed cell death and cell transformation probabilities were lower when considering deposition and clearance simultaneously, compared to the case when only deposition was considered. However, cellular damage remained clustered.

Change of Antioxidant Enzyme Activity during Low-Temperature Hardening of Nicotiana tabacum L. and Secale cereale L.

Changes in the activity of superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) for the plants Nicotiana tabacum L. and Secale cereale L. during low-temperature hardening have been investigated. It was determined that a transient increase in the content of MDA occurs in tobacco plants at the beginning of the hardening period with subsequent activation of SOD, APX, and CAT. Unlike tobacco, winter rye has an MDA content and activity of SOD, APX, and CAT throughout the hardening period that remains at the level of unhardened plants. In tobacco cells, the majority of SOD activity was detected in chloroplasts (90%), while other cellular structures accounted for only 10% of the total activity identified in PAGE. In winter rye cells, SOD activity was distributed evenly between chloroplasts and other cellular compartments (46% in chloroplasts and 54% outside of chloroplasts). The distribution of APX and CAT activity in tobacco and winter rye cells was identical: all APX was concentrated in chloroplasts, while all catalase activity was manifested outside of chloroplasts. It is concluded that tobacco and winter rye plants showed different antioxidant defense strategies under conditions of low hardening temperatures. Tobacco plants provided protection against oxidative damage during low-temperature hardening by increasing activity of SOD, APX, and CAT. Winter rye plants were able to avoid the development of oxidative stress during hardening due to uniform distribution of SOD activity in cells, maintaining the constitutive activity of SOD, APX, and CAT, and, probably, due to the accumulation of nonenzymatic antioxidants.

Radionuclide spatial distribution and dose deposition for in vitro assessments of 212 Pb-αVCAM-1 targeted alpha therapy.

Targeted alpha therapy (TAT) takes advantage of the short-range and high-linear energy transfer of α-particles and is increasingly used, especially for the treatment of metastatic lesions. Nevertheless, dosimetry of α-emitters is challenging for the very same reasons, even for in vitro experiments. Assumptions, such as the uniformity of the distribution of radionuclides in the culture medium, are commonly made, which could have a profound impact on dose calculations. In this study we measured the spatial distribution of α-emitting 212 Pb coupled to an anti-VCAM-1 antibody (212 Pb-αVCAM-1) and its evolution over time in the context of in vitro irradiations. Two experimental setups were implemented without cells to measure α-particle count rates and energy spectra in culture medium containing 15kBq of 212 Pb-α-VCAM-1. Silicon detectors were placed above and below cell culture dishes for 20h. One of the dishes had a 2.5-µm-thick mylar-base allowing easy detection of the α-particles. Monte Carlo simulations were performed to analyze experimental spectra. Experimental setups were modeled and α-energy spectra were simulated in the silicon detectors for different decay positions in the culture medium. Simulated spectra were then used to deconvolute experimental spectra to determine the spatial distribution of 212 Pb-αVCAM-1 in the medium. This distribution was finally used to calculate the dose deposition in cell culture experiments. Experimental count rates and energy spectra showed differences in measurements taken at the top and the bottom of dishes and temporal variations that did not follow 212 Pb decay. The radionuclide spatial distribution was shown to be composed of a uniform distribution and concentration gradients at the top and the bottom, which were subjected to temporal variations that may be explained by gravity and electrostatic attraction. The absorbed dose in cells calculated from this distribution was compared with the dose expected for a uniform and static distribution and found to be 1.75 times higher, which is highly significant to interpret biological observations. This study demonstrated that accurate dosimetry of α-emitters requires the experimental determination of radionuclide spatial and temporal distribution and highlighted that in vitro assessment of dose for TAT cannot only rely on a uniform distribution of activity in the culture medium. The reliability and reproducibility of future experiments should benefit from specifically developed dosimetry tools and methods.

Fabrication of miniature 141Ce sources by chemical deposition towards possible use in the performance evaluation of gamma cameras - A feasibility study

141Ce sources were fabricated for quality assurance of gamma cameras. The fabrication process consisted of electro-deposition of Ni on a Cu sphere in 0.01 N H2SO4 containing 30 mg/mL H3BO3 and 50 μg of NiSO4·7H2O at pH 2–3 followed by deposition of 141Ce on it. > 95% deposition of 141Ce on substrate could be achieved at pH 5. Source core was loaded in custom-made Al holder. Autoradiography confirmed uniform activity distribution. SEM and EDS analyses confirmed deposition of Cerium on substrate.

Removal of methylene dye using composites of poly (styrene-co-acrylonitrile) nanofibers impregnated with adsorbent materials

AimThe current study focus on the evaluation of the enhancing effect of carbonaceous materials incorporation on poly (St-co-AN) nanofibers adsorptive capacity towards cationic methylene blue dye. Materials & methodsPoly (St-co-AN) nanofibers were fabricated using the electrospinning technique. The polymeric material was impregnated with natural materials such as graphite and carbon nanotubes to enhance the formed nanofibers adsorptive properties. The formed nanofibers were applied in the removal of Methylene Blue dye from wastewater. The removal process parameters such as (initial pollutant concentration, pH of the medium, and treatment time) have been studied. Isothermal and kinetic studies of Methylene Blue adsorption ontothe nanofibers surface were done to investigate the adsorption process behavior. Results & discussionsThe heat of sorption was evaluated by Temkin to be 25.34J/mol.and also qm of poly (AN-co-St), Poly (AN-co-St)/graphite and Poly (AN-co-St)/CNTs are found 17.77, 20.34 and 24.69mg/g, respectively. The mechanism of the removal proves was found to be chemisorptions according to boyd and Elovich models, in addition to the uniform activity distribution onto the surface of poly(St-co-AN) nanofibers with a monolayer coverage of methylene blue molecules by Langmuir. Pseudo 2nd order is more appropriate to describe the adsorption process.

Simulated Tremor Propagation in the Upper Limb: From Muscle Activity to Joint Displacement.

Although tremor is the most common movement disorder, there are few noninvasive treatment options. Creating effective tremor suppression devices requires a knowledge of where tremor originates mechanically (which muscles) and how it propagates through the limb (to which degrees-of-freedom (DOF)). To simulate tremor propagation, we created a simple model of the upper limb, with tremorogenic activity in the 15 major superficial muscles as inputs and tremulous joint displacement in the seven major DOF as outputs. The model approximated the muscle excitation-contraction dynamics, musculoskeletal geometry, and mechanical impedance of the limb. From our simulations, we determined fundamental principles for tremor propagation: (1) The distribution of tremor depends strongly on musculoskeletal dynamics. (2) The spreading of tremor is due to inertial coupling (primarily) and musculoskeletal geometry (secondarily). (3) Tremorogenic activity in a given muscle causes significant tremor in only a small subset of DOF, though these affected DOF may be distant from the muscle. (4) Assuming uniform distribution of tremorogenic activity among muscles, tremor increases proximal-distally, and the contribution from muscles increases proximal-distally. (5) Although adding inertia (e.g., with weighted utensils) is often used to suppress tremor, it is possible to increase tremor by adding inertia to the wrong DOF. (6) Similarly, adding viscoelasticity to the wrong DOF can increase tremor. Based solely on the musculoskeletal system, these principles indicate that tremor treatments targeting muscles should focus first on the distal muscles, and devices targeting DOF should focus first on the distal DOF.

Objective evaluation of physical activity pattern using smart devices

Physical activity session frequency and distribution over time may play a significant role on survival after major cardiovascular events. However, the existing amount-based metrics do not account for these properties, thus the physical activity pattern is not fully evaluated. The aim of this work is to introduce a metric which accounts for the difference between the actual and uniform distribution of physical activity, thus its value depends on physical activity aggregation over time. The practical application is demonstrated on a step data from 40 participants, half of them diagnosed with chronic cardiovascular disease (CVD). The metric is capable of discriminating among different daily patterns, including going to and from work, walking in a park and being active the entire day. Moreover, the results demonstrate the tendency of CVD patients being associated with higher aggregation values, suggesting that CVD patients spend more time in a sedentary behaviour compared to healthy participants. By combining the aggregation with the intensity metric, such common weekly patterns as inactivity, regular activity and “weekend warrior” can be captured. The metric is expected to have clinical relevance since it may provide additional information on the relationship between physical activity pattern and health outcomes.

Quantitative radiomics: Validating image textural features for oncological PET in lung cancer

Background and purposeRadiomics textural features derived from PET imaging are of broad and current interest due to recent evidence of their prognostic value during cancer management. An inherent assumption is the link between these imaging features and the underlying tumoral phenotypic spatial heterogeneity. The purpose of this work was to validate this assumption for tumors within the lung through a comparison of image based textural features and the ground truth activity distribution from which the images were created. A second purpose was to assess the level at which PET imaging introduces spatial texture not present in the associated ground truth activity distribution. Materials and methods25 lung lesions were created using an anthropomorphic phantom. Ten of the lesions had a spherical shape with a uniform activity distribution. The remaining 15 had an irregular shape with a heterogeneous activity distribution. PET images were created for each lesion using Monte Carlo simulation. 79 textural features related to the gray-level intensity histograms, co-occurrence matrices, neighborhood difference matrices, run length, and size zone matrices were derived from both the simulated PET images and ground truth activity maps. A comparison was made between the two datasets using statistical analysis. ResultsFor homogenous lesions, features extracted from the PET images were largely irrelevant to the underlying uniform activity distribution. Additionally, the majority of these features assumed substantial values implying that an extensive amount of spatial texture had been introduced into the final imaging data. For heterogeneous lesions, complex trends were observed in the deviation between features extracted from PET images and those extracted from the ground truth activity maps. Moreover, the extent of both the deviation and the associated dynamic range was seen to be greatly feature-dependent. ConclusionThe use of image based textural features as a surrogate for tumoral phenotypic spatial heterogeneity could not be clearly validated. The association between the two is complex and a significant amount of uncertainty exist due to the introduction of incidental texture during image acquisition and reconstruction.

Measurement of activity distribution in an Am-241 disc source using peeled-off Gafchromic EBT3 films

Commercial alpha-emitting sources are fabricated mainly in a disc type. An alpha particle irradiator in Radiation Bioengineering Laboratory at Seoul National University was installed with an Am-241 disc source. Commercial Am-241 disc sources are fabricated by incorporating the radioactive element into a thin substrate layer. Those disc sources are utilized assuming that the radioactive element is uniformly distributed in the active layer of disc sources. In this study, we employed peeled-off Gafchromic EBT3 films to investigate the uniformity of areal radioactivity density over the disc source and to measure the effect of non-uniform activity distribution on dose distribution at the bottom of the cell culture dish positioned in a varying distance from the source. The measurements with the peeled-off EBT3 films informed that the areal activity density in the disc source differed by up to approximately 45% from the average. However, the inhomogeneous Am-241 distribution in a disc source did not affect the radial distribution of fluence rate at the inner bottom of cell dish when the dish is apart from the source sufficiently. The dose distribution measured with an EBT3 film nearly accorded with that obtained by Monte Carlo simulation assuming the uniform Am-241 activity distribution in the active layer of the disc source. Finally, the dose to a single-cell layer of 5 μm in a nominal thickness was obtained by Monte Carlo simulation assuming a uniform Am-241 activity distribution in the disc source at distances of 20 and 30 mm from the source. The cellular dose estimates were higher than the film dose estimates at all radial distances. The cellular dose decreased with an increasing radial distance from the center to a smaller extent than the EBT3 film dose did.

Phantom validation of quantitative Y-90 PET/CT-based dosimetry in liver radioembolization

BackgroundPET/CT has recently been shown to be a viable alternative to traditional post-infusion imaging methods providing good quality images of 90Y-laden microspheres after selective internal radiation therapy (SIRT). In the present paper, first we assessed the quantitative accuracy of 90Y-PET using an anthropomorphic phantom provided with lungs, liver, spine, and a cylindrical homemade lesion located into the hepatic compartment. Then, we explored the accuracy of different computational approaches on dose calculation, including (I) direct Monte Carlo radiation transport using Raydose, (II) Kernel convolution using Philips Stratos, (III) local deposition algorithm, (IV) Monte Carlo technique (MCNP) considering a uniform activity distribution, and (V) MIRD (Medical Internal Radiation Dose) analytical approach. Finally, calculated absorbed doses were compared with those obtained performing measurements with LiF:Mg,Cu,P TLD chips in a liquid environment.ResultsOur results indicate that despite 90Y-PET being likely to provide high-resolution images, the 90Y low branch ratio, along with other image-degrading factors, may produce non-uniform activity maps, even in the presence of uniform activity. A systematic underestimation of the recovered activity, both for the tumor insert and for the liver background, was found. This is particularly true if no partial volume correction is applied through recovery coefficients. All dose algorithms performed well, the worst case scenario providing an agreement between absorbed dose evaluations within 20%. Average absorbed doses determined with the local deposition method are in excellent agreement with those obtained using the MIRD and the kernel-convolution dose calculation approach.Finally, absorbed dose assessed with MC codes are in good agreement with those obtained using TLD in liquid solution, thus confirming the soundness of both calculation approaches. This is especially true for Raydose, which provided an absorbed dose value within 3% of the measured dose, well within the stated uncertainties.ConclusionsPatient-specific dosimetry is possible even in a scenario with low true coincidences and high random fraction, as in 90Y–PET imaging, granted that accurate absolute PET calibration is performed and acquisition times are sufficiently long. Despite Monte Carlo calculations seeming to outperform all dose estimation algorithms, our data provide a strong argument for encouraging the use of the local deposition algorithm for routine 90Y dosimetry based on PET/CT imaging, due to its simplicity of implementation.