Results of an interlaboratory study on the working curve in vat photopolymerization.

The working curve informs resin properties and print parameters for stereolithography, digital light processing, and other photopolymer additive manufacturing (PAM) technologies. First demonstrated in 1992, the working curve measurement of cure depth vs radiant exposure of light is now a foundational measurement in the field of PAM. Despite its widespread use in industry and academia, there is no formal method or procedure for performing the working curve measurement, raising questions about the utility of reported working curve parameters. Here, an interlaboratory study (ILS) is described in which 24 individual laboratories performed a working curve measurement on an aliquot from a single batch of PAM resin. The ILS reveals that there is enormous scatter in the working curve data and the key fit parameters derived from it. The measured depth of light penetration Dp varied by as much as 7x between participants, while the critical radiant exposure for gelation Ec varied by as much as 70x. This significant scatter is attributed to a lack of common procedure, variation in light engines, epistemic uncertainties from the Jacobs equation, and the use of measurement tools with insufficient precision. The ILS findings highlight an urgent need for procedural standardization and better hardware characterization in this rapidly growing field.

Effect of density dependence on coinfection dynamics.

In this paper we develop a compartmental model of SIR type (the abbreviation refers to the number of Susceptible, Infected and Recovered people) that models the population dynamics of two diseases that can coinfect. We discuss how the underlying dynamics depends on the carrying capacity K: from a simple dynamics to a more complex. This can also help in understanding the appearance of more complicated dynamics, for example, chaos and periodic oscillations, for large values of K. It is also presented that pathogens can invade in population and their invasion depends on the carrying capacity K which shows that the progression of disease in population depends on carrying capacity. More specifically, we establish all possible scenarios (the so-called transition diagrams) describing an evolution of an (always unique) locally stable equilibrium state (with only non-negative compartments) for fixed fundamental parameters (density independent transmission and vital rates) as a function of the carrying capacity K. An important implication of our results is the following important observation. Note that one can regard the value of K as the natural 'size' (the capacity) of a habitat. From this point of view, an isolation of individuals (the strategy which showed its efficiency for COVID-19 in various countries) into smaller resp. larger groups can be modelled by smaller resp. bigger values of K. Then we conclude that the infection dynamics becomes more complex for larger groups, as it fairly maybe expected for values of the reproduction number R 0 ≈ 1 . We show even more, that for the values R 0 > 1 there are several (in fact four different) distinguished scenarios where the infection complexity (the number of nonzero infected classes) arises with growing K. Our approach is based on a bifurcation analysis which allows to generalize considerably the previous Lotka-Volterra model considered previously in Ghersheen et al. (Math Meth Appl Sci 42(8), 2019).

PET/MRI of glucose metabolic rate, lipid content and perfusion in human brown adipose tissue.

This study evaluated the MRI-derived fat fraction (FF), from a Cooling-reheating protocol, for estimating the cold-induced brown adipose tissue (BAT) metabolic rate of glucose (MRglu) and changes in lipid content, perfusion and arterial blood volume (VA) within cervical-supraclavicular fat (sBAT). Twelve volunteers underwent PET/MRI at baseline, during cold exposure and reheating. For each temperature condition, perfusion and VA were quantified with dynamic [15O]water-PET, and FF, with water-fat MRI. MRglu was assessed with dynamic [18F]fluorodeoxyglucose-PET during cold exposure. sBAT was defined using anatomical criteria, and its subregion sBATHI, by MRglu > 11 µmol/100 cm3/min. For all temperature conditions, sBAT-FF correlated negatively with sBAT-MRglu (ρ ≤ - 0.87). After 3 h of cold, sBAT-FF decreased (- 2.13 percentage points) but tended to normalize during reheating although sBATHI-FF remained low. sBAT-perfusion and sBAT-VA increased during cold exposure (perfusion: + 5.2 ml/100 cm3/min, VA: + 4.0 ml/100 cm3). sBAT-perfusion remained elevated and sBAT-VA normalized during reheating. Regardless of temperature condition during the Cooling-reheating protocol, sBAT-FF could predict the cold-induced sBAT-MRglu. The FF decreases observed after reheating were mainly due to lipid consumption, but could potentially be underestimated due to intracellular lipid replenishment. The influence of perfusion and VA, on the changes in FF observed during cold exposure, could not be ruled out.

Estimating the cold-induced brown adipose tissue glucose uptake rate measured by 18F-FDG PET using infrared thermography and water-fat separated MRI.

Brown adipose tissue (BAT) expends chemical energy to produce heat, which makes it a potential therapeutic target for combating metabolic dysfunction and overweight/obesity by increasing its metabolic activity. The most well-established method for measuring BAT metabolic activity is glucose uptake rate (GUR) measured using 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET). However, this is expensive and exposes the subjects to potentially harmful radiation. Cheaper and safer methods are warranted for large-scale or longitudinal studies. Potential alternatives include infrared thermography (IRT) and magnetic resonance imaging (MRI). The aim of this study was to evaluate and further develop these techniques. Twelve healthy adult subjects were studied. The BAT GUR was measured using 18F-FDG PET during individualized cooling. The temperatures of the supraclavicular fossae and a control region were measured using IRT during a simple cooling protocol. The fat fraction and effective transverse relaxation rate of BAT were measured using MRI without any cooling intervention. Simple and multiple linear regressions were employed to evaluate how well the MRI and IRT measurements could estimate the GUR. Results showed that both IRT and MRI measurements correlated with the GUR. This suggest that these measurements may be suitable for estimating the cold-induced BAT GUR in future studies.

Brown adipose tissue estimated with the magnetic resonance imaging fat fraction is associated with glucose metabolism in adolescents.

BACKGROUND: Despite therapeutic potential against obesity and diabetes, the associations of brown adipose tissue (BAT) with glucose metabolism in young humans are relatively unexplored. OBJECTIVES: To investigate possible associations between magnetic resonance imaging (MRI) estimates of BAT and glucose metabolism, whilst considering sex, age, and adiposity, in adolescents with normal and overweight/obese phenotypes. METHODS: In 143 subjects (10-20 years), MRI estimates of BAT were assessed as cervical-supraclavicular adipose tissue (sBAT) fat fraction (FF) and T2* from water-fat MRI. FF and T2* of neighbouring subcutaneous adipose tissue (SAT) were also assessed. Adiposity was estimated with a standardized body mass index, the waist-to-height ratio, and abdominal visceral and subcutaneous adipose tissue volumes. Glucose metabolism was represented by the 2h plasma glucose concentration, the Matsuda index, the homeostatic model assessment of insulin resistance, and the oral disposition index; obtained from oral glucose tolerance tests. RESULTS: sBAT FF and T2* correlated positively with adiposity before and after adjustment for sex and age. sBAT FF, but not T2* , correlated with 2h glucose and Matsuda index, also after adjustment for sex, age, and adiposity. The association with 2h glucose persisted after additional adjustment for SAT FF. CONCLUSIONS: The association between sBAT FF and 2h glucose, observed independently of sex, age, adiposity, and SAT FF, indicates a role for BAT in glucose metabolism, which potentially could influence the risk of developing diabetes. The lacking association with sBAT T2* might be due to FF being a superior biomarker for BAT and/or to methodological limitations in the T2* quantification.

Metabolic Risk Factors Associated with Visceral and Subcutaneous Adipose Tissue in a Sex-Specific Manner in Seven-Year-Olds.

OBJECTIVE: This study aimed to investigate how visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) volumes were associated with metabolic risk factors in 7-year-old children. METHODS: A total of 81 children (52% girls) from a Swedish birth cohort were studied. At 6 years of age, anthropometric data, fasting insulin, glucose, cholesterol, and blood pressure were collected on 53 children with normal weight and 28 children with overweight or obesity, and insulin resistance was estimated. At 7 years of age, magnetic resonance imaging quantified VAT and SAT. Sex and regression analyses were conducted. RESULTS: SAT was more strongly associated with metabolic risk factors than VAT. The associations between VAT and metabolic risk factors were stronger in girls (P < 0.05). When VAT was adjusted for birth weight and maternal BMI and education, it accounted for 51% of insulin variance (ß = 11.72; P = 0.001) but only in girls. The key finding of this study was that adjusted SAT accounted for 63% of the fasting insulin variance in girls (ß = 2.76; P < 0.001). Waist circumference was the best anthropometric marker for insulin resistance. CONCLUSIONS: Insulin resistance was associated with abdominal adipose tissue and its associated metabolic risk factors in children as young as 7 years old.

Separation of water and fat signal in whole-body gradient echo scans using convolutional neural networks.

PURPOSE: To perform and evaluate water-fat signal separation of whole-body gradient echo scans using convolutional neural networks. METHODS: Whole-body gradient echo scans of 240 subjects, each consisting of 5 bipolar echoes, were used. Reference fat fraction maps were created using a conventional method. Convolutional neural networks, more specifically 2D U-nets, were trained using 5-fold cross-validation with 1 or several echoes as input, using the squared difference between the output and the reference fat fraction maps as the loss function. The outputs of the networks were assessed by the loss function, measured liver fat fractions, and visually. Training was performed using a graphics processing unit (GPU). Inference was performed using the GPU as well as a central processing unit (CPU). RESULTS: The loss curves indicated convergence, and the final loss of the validation data decreased when using more echoes as input. The liver fat fractions could be estimated using only 1 echo, but results were improved by use of more echoes. Visual assessment found the quality of the outputs of the networks to be similar to the reference even when using only 1 echo, with slight improvements when using more echoes. Training a network took at most 28.6 h. Inference time of a whole-body scan took at most 3.7 s using the GPU and 5.8 min using the CPU. CONCLUSION: It is possible to perform water-fat signal separation of whole-body gradient echo scans using convolutional neural networks. Separation was possible using only 1 echo, although using more echoes improved the results.

MRI estimates of brown adipose tissue in children - Associations to adiposity, osteocalcin, and thigh muscle volume.

CONTEXT: Brown adipose tissue is of metabolic interest. The tissue is however poorly explored in children. METHODS: Sixty-three 7-year old subjects from the Swedish birth-cohort Halland Health and Growth Study were recruited. Care was taken to include both normal weight and overweight children, but the subjects were otherwise healthy. Only children born full term were included. Water-fat separated whole-body MRI scans, anthropometric measurements, and measurements of fasting glucose and levels of energy homeostasis related hormones, including the insulin-sensitizer osteocalcin, were performed. The fat fraction (FF) and effective transverse relaxation time (T2*) of suspected brown adipose tissue in the cervical-supraclavicular-axillary fat depot (sBAT) and the FFs of abdominal visceral (VAT) and subcutaneous adipose tissue (SAT) were measured. Volumes of sBAT, abdominal VAT and SAT, and thigh muscle volumes were measured. RESULTS: The FF in the sBAT depot was lower than in VAT and SAT for all children. In linear correlations including sex and age as explanatory variables, sBAT FF correlated positively with all measures of adiposity (p < 0.01), except for VAT FF and weight, positively with sBAT T2* (p = 0.036), and negatively with osteocalcin (p = 0.017). When adding measures of adiposity as explanatory variables, sBAT FF also correlated negatively with thigh muscle volume (p < 0.01). CONCLUSIONS: Whole-body water-fat MRI of children allows for measurements of sBAT. The FF of sBAT was lower than that of VAT and SAT, indicating presence of BAT. Future studies could confirm whether the observed correlations corresponds to a hormonally active BAT.

Water-fat separation incorporating spatial smoothing is robust to noise.

PURPOSE: To develop and evaluate a noise-robust method for reconstruction of water and fat images for spoiled gradient multi-echo sequences. METHODS: The proposed method performs water-fat separation by using a graph cut to minimize an energy function consisting of unary and binary terms. Spatial smoothing is incorporated to increase robustness to noise. The graph cut can fail to find a solution covering the entire image, in which case the relative weighting of the unary term is iteratively increased until a complete solution is found. The proposed method was compared to two previously published methods. Reconstructions were performed on 16 cases taken from the 2012 ISMRM water-fat reconstruction challenge dataset, for which reference reconstructions were provided. Robustness towards noise was evaluated by reconstructing images with different levels of noise added. The percentage of water-fat swaps were calculated to measure performance. RESULTS: At low noise levels the proposed method produced similar results to one of the previously published methods, while outperforming the other. The proposed method significantly outperformed both of the previously published methods at moderate and high noise levels. CONCLUSION: By incorporating spatial smoothing, an increased robustness towards noise is achieved when performing water-fat reconstruction of spoiled gradient multi-echo sequences.

Resistance training enhances insulin suppression of endogenous glucose production in elderly women.

An altered prenatal environment during maternal obesity predisposes offspring to insulin resistance, obesity, and their consequent comorbidities, type 2 diabetes and cardiovascular disease. Telomere shortening and frailty are additional risk factors for these conditions. The aim of this study was to evaluate the effects of resistance training on hepatic metabolism and ectopic fat accumulation. Thirty-five frail elderly women, whose mothers' body mass index (BMI) was known, participated in a 4-mo resistance training program. Endogenous glucose production (EGP) and hepatic and visceral fat glucose uptake were measured during euglycemic hyperinsulinemia with [(18)F]fluorodeoxyglucose and positron emission tomography. Ectopic fat was measured using magnetic resonance spectroscopy and imaging. We found that the training intervention reduced EGP during insulin stimulation [from 5.4 (interquartile range 3.0, 7.0) to 3.9 (-0.4, 6.1) µmol·kg body wt(-1)·min(-1), P = 0.042] in the whole study group. Importantly, the reduction was higher among those whose EGP was more insulin resistant at baseline (higher than the median) [-5.6 (7.1) vs. 0.1 (5.4) µmol·kg body wt(-1)·min(-1), P = 0.015]. Furthermore, the decrease in EGP was associated with telomere elongation (r = -0.620, P = 0.001). The resistance training intervention did not change either hepatic or visceral fat glucose uptake or the amounts of ectopic fat. Maternal obesity did not influence the studied measures. In conclusion, resistance training improves suppression of EGP in elderly women. The finding of improved insulin sensitivity of EGP with associated telomere lengthening implies that elderly women can reduce their risk for type 2 diabetes and cardiovascular disease with resistance training.

Resistance training improves skeletal muscle insulin sensitivity in elderly offspring of overweight and obese mothers.

AIMS/HYPOTHESIS: Maternal obesity predisposes offspring to adulthood morbidities, including type 2 diabetes. Type 2 diabetes and insulin resistance have been associated with shortened telomere length. First, we aimed to investigate whether or not maternal obesity influences insulin sensitivity and its relationship with leucocyte telomere length (LTL) in elderly women. Second, we tested whether or not resistance exercise training improves insulin sensitivity in elderly frail women. METHODS: Forty-six elderly women, of whom 20 were frail offspring of lean/normal weight mothers (OLM, BMI ≤26.3 kg/m2) and 17 were frail offspring of overweight/obese mothers (OOM,BMI ≥28.1 kg/m2), were studied before and after a 4 month resistance training (RT) intervention. Muscle insulin sensitivity of glucose uptake was measured using 18F-fluoro-2-deoxyglucose and positron emission tomography with computed tomography during a hyperinsulinaemic­euglycaemic clamp. Muscle mass and lipid content were measured using magnetic resonance and LTL was measured using real-time PCR. RESULTS: The OOM group had lower thigh muscle insulin sensitivity compared with the OLM group (p=0.048) but similar whole body insulin sensitivity. RT improved whole body and skeletal muscle insulin sensitivity in the OOM group only (p=0.004 and p=0.013, respectively), and increased muscle mass in both groups (p <0 .01). In addition, in the OOM group, LTL correlated with different thigh muscle groups insulin sensitivity (ρ ≥ 0.53; p ≤ 0.05). Individuals with shorter LTL showed a higher increase in skeletal muscle insulin sensitivity after training (ρ ≥ −0.61; p ≤ 0.05). CONCLUSIONS/INTERPRETATION: Maternal obesity and having telomere shortening were associated with insulin resistance in adult offspring. A resistance exercise training programme may reverse this disadvantage among offspring of obese mothers. Trial registration: ClinicalTrials.gov NCT01931540.