Residual Standard Deviation Research Articles

Description of the growth of pequi fruits by nonlinear models

Abstract Pequi tree is a species native to the Brazilian cerrado, with wide geographic distribution, whose fruit is very appreciated in cooking, composing traditional dishes. In general, pequi fruit is consumed when ripe in the fresh form or in the various derived products such as oils, liqueurs, sweets, ice creams among others, involving important socioeconomic activity generating employment and income in family agriculture. The aim of this study was to evaluate the adjustment of Brody, Gompertz, Logistic and Von Bertalanffy models in the growth and development of pequi fruits based on their physical characteristics such as longitudinal and cross-sectional diameter and fresh mass obtained over time. Parameters were estimated using R software routines, using the least squares method and the Gauss-Newton iterative process. The adjustment of models was compared using the following criteria: residual standard deviation, adjusted determination coefficient and corrected Akaike information criterion. In general, data presented no correlation error structure and the Von Bertalanffy model did not fit fresh mass data. The models presented good quality in the adjustment to pequi growth data, except for the Brody model for fresh mass. The Gompertz and Logistic models were those that best described variables, and the Gompertz model was the most suitable to describe diameter and mass data. Based on the adjustment, a slow initial growth was observed up to about 20 days after anthesis; after this period, the fruit developed more rapidly up to 90 days and then presented a tendency to stability until the end of the evaluation period at 117 days after anthesis, with sigmoid curve character. Pequi fruits obtained final average value of 7.1 cm for cross-sectional diameter, 6.8 cm for longitudinal diameter and 113g for fresh mass.

Editors' note: Blood pressure from mid- to late life and risk of incident dementia

In “Blood pressure from mid- to late life and risk of incident dementia,” authors McGrath et al. found that elevated blood pressure (BP) during midlife, persistence of elevated BP into late life, and, among nonhypertensive patients, a steep decline in BP during mid- to late life were associated with an increased dementia risk. Commenting on the article, Drs. Lattanzi and Silvestrini suggest that the analysis of the pulsatile component of BP through pulse pressure, and the BP variability through average real variability, or residual SD, which takes account of temporal trends in BP, could provide a more nuanced perspective of the mechanisms linking vascular aging to neurodegeneration, and add insights toward potential future therapy. Commenting on the same article, Dr. Ganesh makes similar observations and suggests that home readings may allow better monitoring of BP variability. Authors McGrath et al. agree that further exploration of the relationship between blood pressure measures and dementia is necessary and acknowledge that incorporating additional blood pressure measures may provide useful insight into this relationship. In “Blood pressure from mid- to late life and risk of incident dementia,” authors McGrath et al. found that elevated blood pressure (BP) during midlife, persistence of elevated BP into late life, and, among nonhypertensive patients, a steep decline in BP during mid- to late life were associated with an increased dementia risk. Commenting on the article, Drs. Lattanzi and Silvestrini suggest that the analysis of the pulsatile component of BP through pulse pressure, and the BP variability through average real variability, or residual SD, which takes account of temporal trends in BP, could provide a more nuanced perspective of the mechanisms linking vascular aging to neurodegeneration, and add insights toward potential future therapy.

Reader response: Blood pressure from mid- to late life and risk of incident dementia.

We read with interest the article by McGrath et al.,1 which reported a significant association between elevated mid-life blood pressure (BP), persistent late-life BP, steep mid-to-late life BP decline, and risk of dementia, and underscored the vascular contribution to cognitive dysfunction. The exact role of vascular disease in the pathophysiology of Alzheimer disease (AD) and non-AD dementias remains unclear. The analysis of reliable hemodynamic measures besides BP trajectories, like the pulsatile component of BP through pulse pressure,2 and the BP variability through average real variability,3–5 which accounts for the order of BP measurements over time, or residual SD, which takes account of temporal trends in BP, may be advisable. These measures could provide a more nuanced perspective of the mechanisms linking vascular aging to neurodegeneration, and add useful insights toward potential future therapeutic horizons.

Etalon fringe removal of tunable diode laser multi-pass spectroscopy by wavelet transforms

Tunable diode laser absorption spectroscopy (TDLAS) is an important technique for trace gas detection. The sensitivity of TDLAS system, especially for multi-pass absorption, is usually limited by optical fringes. It is an effective approach to suppressing optical fringes of spectral lines using digital filtering. The parameters derived from filtering simulations are key factors and they are related to the noise characteristic. In the paper, the precise Airy functions were used to simulate optical interference and the interference signal was effectively minimized by the wavelet transforms. The root-mean-square error and the residual standard deviation are introduced to quantify the suppression ratio of etalon fringes. It is demonstrated that the optimum wavelet function in denoising the observed CO2 lines is fk18, in comparison with haar, db02, coif1 etc. In addition, the absorption signals recorded by direct absorption spectroscopy and wavelength modulation spectroscopy at second-harmonic (WMS-2f) with a 10 m White-type cell were subjected to low-pass, averaging and fk18 wavelet filtering, respectively. The results show that only wavelet transform is capable of suppressing optical interference noise. The detection limit of WMS-2f can reach 7 ppm and the perfect calibration curves between signal intensity and gas concentration are obtained after wavelet filtering. To further demonstrate the feasibility of the approach, spectral signals at different pressures and temperatures were acquired and the etalon interference is substantially eliminated by fk18 wavelet at 13th level of decomposition.

PATHOPHYSIOLOGY OF HYPERTENSION

Objective: The Xenon-133 washout technique can be used to assess mean renal blood flow as well as intrarenal blood flow patterns. Disappearance of tracer from the kidney generally follows either a bi-exponential or a mono-exponential decay pattern. The latter pattern suggest homogenization of blood flow. In addition, oscillatory patterns in the decay curves may point to local vasomotor activity. In this study, we compared patients with essential hypertension (EH) to patients with hypertension due to fibromuscular dysplasia (FMD) or atherosclerotic renal artery stenosis (ARAS) to assess possible differences in Xenon washout characteristics between these groups. Design and method: Renal blood flow was measured by injecting Xenon-133 gas through a catheter placed in the renal artery and monitoring the disappearance of the isotope within 180 seconds. The acquired curves were fitted to one- or two-phase decay models and oscillation in the curves was calculated using standard deviation of residuals. All measurements were obtained before contrast was injected. Results: There were no differences in the number of one-phase or two-phase fits between groups (p = 0.135). For two-phase decays, the fast component was markedly lower in both FMD and ARAS groups compared to EH (p < 0.001). The slow component was lower in ARAS compared to EH (p = 0.002). Mono-exponential decay values did not differ significantly between groups (p = 0.088). Oscillations in curves were lesser in EH as compared to both FMD (p = 0.004) and ARAS (p < 0.001). Conclusions: A fall in the fast blood flow component in FMD and ARAS may be due to either redistribution of blood flow from cortical nephrons with a high perfusion rate to deeper nephrons with slower flow rates or to possible recruitment of ‘dormant’ cortical nephrons. Differences between ARAS and FMD groups in fast and slow flow could mean that the responsible pathophysiological process has proceeded further in ARAS compared to FMD. Enhanced oscillation patterns may be due to an increase in local vasomotor activity. Lesser oscillation in EH patients could mean that this pathophysiological process is not activated in this group.

An Improved Protocol for Performing Two-Way Satellite Time and Frequency Transfer Using a Satellite in an Inclined Geo-Synchronous Orbit.

Two-way satellite time and frequency transfer (TWSTFT) using satellites in inclined geo-synchronous orbit (IGSO) is fundamentally more difficult than using satellites in geostationary orbit (GEO), due to the fact that IGSO satellites are constantly moving relative to a ground station, which brings in large residual effects. In this paper, we designed a protocol and an algorithm to correct several factors that affect the precision of TWSTFT using IGSO satellites. We used two ground stations, each equipped with sending and receiving channels, to conduct real-time measurements of the distance and the speed of an IGSO satellite, and data collected were used to make appropriate corrections. We tested this concept by conducting TWSTFT experiments using an IGSO satellite (BEIDOU I1-S), and compared the results with that obtained using a GEO satellite (CHINASAT 12). Indeed, the individual components that contribute to the residual effects of TWSTFT measurements using the IGSO satellite were several orders of magnitude greater than that of the GEO satellite. By using our modified protocol, TWSTFT results with an IGSO satellite were well accorded with that of using a GEO satellite; the standard deviation of residuals was less than 0.4 ns, well within the limit for the measurement uncertainty of TWSTFT. Therefore, we have expanded the use of IGSO satellites for TWSTFT. In principle, it should also be applicable to medium earth orbit and other satellites.

Echocardiographic Analysis of Cardiac Function after Infarction in Mice: Validation of Single-Plane Long-Axis View Measurements and the Bi-Plane Simpson Method

Although echocardiography is commonly used to analyze cardiac function in small animal models of cardiac remodeling after myocardial infarction, the different echocardiographic methods are validated poorly. End-diastolic volume, end-systolic volume and ejection fraction were analyzed using either standard single-plane analysis from parasternal long-axis B-mode views (PSLAX) or the bi-plane Simpson method (using PSLAX and three short-axis views) and validated using magnetic resonance imaging as standard. Ejection fraction measured by PSLAX was moderately correlated with a coefficient of R2 = 0.49. The standard deviation of residuals was 9.91. Simpson analysis revealed an improved correlation coefficient of R2 = 0.77 and a reduction in standard deviation of residuals by 45% (5.45 vs. 9.92, p = 0.014). Subgroup analysis revealed that the high variation in PSLAX is due to changes in ventricular geometry after myocardial infarction. Our results indicate that the bi-plane Simpson method is advantageous for the assessment of cardiac function after myocardial infarction.

Optimal design for longitudinal studies to estimate pubertal height growth in individuals

Background: The SITAR model expresses individual pubertal height growth in terms of mean size, peak height velocity (PHV) and age at PHV.Aim: To use SITAR to identify the optimal time interval between measurements to summarise individual pubertal height growth.Subjects and methods: Heights in 3172 boys aged 9–19 years from Christ’s Hospital School measured on 128 679 occasions (a median of 42 heights per boy) were analysed using the SITAR (SuperImposition by Translation And Rotation) mixed effects growth curve model, which estimates a mean curve and three subject-specific random effects. Separate models were fitted to sub-sets of the data with measurement intervals of 2, 3, 4, 6, 12 and 24 months, and the different models were compared.Results: The models for intervals 2–12 months gave effectively identical results for the residual standard deviation (0.8 cm), mean spline curve (6 degrees of freedom) and random effects (correlations >0.9), showing there is no benefit in measuring height more often than annually. The model for 2-year intervals fitted slightly less well, but needed just four-to-five measurements per individual.Conclusions: Height during puberty needs to be measured only annually and, with slightly lower precision, just four biennial measurements can be sufficient.

A Generalized Lidar-Based Model for Predicting the Merchantable Volume of Balsam Fir of Sites Located along a Bioclimatic Gradient in Quebec, Canada

Lidar-based models rely on an optimal relationship between the field and the lidar data for accurate predictions of forest attributes. This relationship may be altered by the variability in the stand growth conditions or by the temporal discrepancy between the field inventory and the lidar survey. In this study, we used lidar data to predict the timber merchantable volume (MV) of five sites located along a bioclimatic gradient of temperature and elevation. The temporal discrepancies were up to three years. We adjusted a random canopy height coefficient (accounting for the variability amongst sites), and a growth function (accounting for the growth during the temporal discrepancy), to the predictive model. The MV could be predicted with a pseudo-R2 of 0.86 and a residual standard deviation of 24.3 m3 ha−1. The average biases between the field-measured and the predicted MVs were small. The variability of MV predictions was related to the bioclimatic gradient. Fixed-effect models that included a bioclimatic variable provided similar prediction accuracies. This study suggests that the variability amongst sites, the occurrence of a bioclimatic gradient and temporal discrepancies are essential in building a generalized lidar-based model for timber volume.

Modelling of Basin Wide Daily Evapotranspiration with a Partial Integration of Remote Sensing Data

Evapotranspiration (ET) is the most significant water balance component and is also a very complex component to evaluate in spatio–temporal scales. Remotely-sensed data greatly increases the accuracy of basin wide ET estimation but only in periods with available satellite images. This paper describes an attempt to estimate daily ET regardless of the availability of the satellite images. The method is based on application of the interpolated evaporative fraction (Λ) from “historical” satellite images to periods with no satellite data available. Basin wide daily ET is obtained by combining interpolated Λ and standard PET methods on meteorological stations. The reliability of such approach was evaluated by comparing the obtained daily ET to the SEBAL ET estimates through the analysis of residuals (Δ), standard deviations of residuals (σ) and the Nash–Sutcliffe coefficient (NSE) over the basin. The SEBAL ET estimates were validated with the data from two lysimeters. The discrepancy of obtained ET versus the SEBAL ET estimates (Δ = 0.13 mm day−1, σ = 0.64 mm day−1, NSE = 0.07) indicated that the proposed concept has relatively high accuracy, which is notably higher than the Penman–Monteith interpolated ET estimates (Δ = 1.94 mm day−1, σ = 1.03 mm day−1, NSE = −4.71). It was shown that a total of five images can provide a reliable estimate of interpolated Λ and thus represent specific characteristics of a basin. As the presented concept requires minimum remote sensing data and ground based inputs, it could be applied to estimate basin wide daily ET in data scarce regions and in periods with no satellite images available.

Kinetic models of Fischer-Tropsch synthesis reaction over granule-type Pt-promoted Co/Al2O3 catalyst

Kinetic models of CO hydrogenation to paraffinic hydrocarbons through Fischer-Tropsch synthesis (FTS) reaction were studied by using Langmuir-Hinshelwood Hougen-Watson (LHHW) model of 16 different reaction steps with a pseudo steady-state assumption (PSSA) on the prototype Pt-promoted Co/Al2O3 catalyst having a granule size of ∼1 mm of spherical γ-Al2O3 support (surface area of 149m2/g). The derived kinetic models from ten sets of experimental data by altering the reaction conditions such as temperatures, pressures, space velocities and H2/CO molar ratios were found to be well fitted with reasonable kinetic parameters and small errors of conversion of CO and hydrocarbon distributions in terms of mean absolute relative residual (MARR) and relative standard deviation error (RSDE). The derived reaction rates and CO activation energy of -86 kJ/mol well correspond to the our previously reported results using power-type catalysts. Based on the LHHW model with PSSA, the possible chemical intermediates on the granule ball-type Co-Pt/Al2O3 surfaces were precisely considered to explain the typical adsorption, initiation, propagation and termination steps of FTS reaction as well as to derive elementary reaction rates with their kinetic parameters and hydrocarbon distributions. The derived kinetic models were further used to verify temperature-profiles in a pilot-scale fixed-bed tubular FTS reactor with a packing depth of 100 cm catalyst, and it confirmed that the temperature gradients were less than 10 °C in a length of reactor by effectively removing the generated heat by an exothermic FTS reaction.

Unary Non-Structural Fertilizer Response Model for Rice Crops and Its Field Experimental Verification

The quadratic polynomial fertilizer response model (QPFM) is the primary method for implementing quantitative fertilization in crop production, but the success rate of this model’s recommended fertilization rates in China is low because the model contains a high setting bias. This paper discusses a new modelling method for expanding the applicability of QPFM. The results of field experiments with 8 levels of N, P, or K fertilization showed that the dynamic trend between rice yield increases and fertilizer application rate exhibited a typical exponential relationship. Therefore, we propose a unary non-structural fertilizer response model (NSFM). The responses of 18 rice field experiments to N, P, or K fertilization indicated that the new models could significantly predict rice yields, while two experimental fitting results using the unary QPFM did not pass statistical significance tests. The residual standard deviations of 13 new models were significantly lower than that of the unary QPFM. The linear correlation coefficient of the recommended application rates between the new model and the unary QPFM reached a significant level. Theoretical analysis showed that the unary QPFM was a simplified version of the new model, and it had a higher fitting precision and better applicability.

Quantitative analysis of Ni2+/Ni3+ in Li[NixMnyCoz]O2 cathode materials: Non-linear least-squares fitting of XPS spectra

Quantitative analysis of Ni2+/Ni3+ using X-ray photoelectron spectroscopy (XPS) is important for evaluating the crystal structure and electrochemical performance of Lithium-nickel–cobalt-manganese oxide (Li[NixMnyCoz]O2, NMC). However, quantitative analysis based on Gaussian/Lorentzian (G/L) peak fitting suffers from the challenges of reproducibility and effectiveness. In this study, the Ni2+ and Ni3+ standard samples and a series of NMC samples with different Ni doping levels were synthesized. The Ni2+/Ni3+ ratios in NMC were quantitatively analyzed by non-linear least-squares fitting (NLLSF). Two Ni 2p overall spectra of synthesized Li [Ni0.33Mn0.33Co0.33]O2(NMC111) and bulk LiNiO2 were used as the Ni2+ and Ni3+ reference standards. Compared to G/L peak fitting, the fitting parameters required no adjustment, meaning that the spectral fitting process was free from operator dependence and the reproducibility was improved. Comparison of residual standard deviation (STD) showed that the fitting quality of NLLSF was superior to that of G/L peaks fitting. Overall, these findings confirmed the reproducibility and effectiveness of the NLLSF method in XPS quantitative analysis of Ni2+/Ni3+ ratio in Li[NixMnyCoz]O2 cathode materials.

Fourier Harmonic Regression Method for Bearing Condition Monitoring using Vibration Measurements

Recently, condition monitoring and fault diagnosis of rolling element bearings in rotary machinery is an important task in industries for system preventive maintenance, increase reliability, improved productivity and increase machine availability. Existing methods for condition monitoring of bearings require extensive experimental arrangements using costly sensors and complex computational techniques in frequency domain for fault diagnosis. This work presents a simple time domain based approach using Fourier harmonic regression analysis method for condition monitoring of rolling element bearings. In the present work, bearing vibrations are acquired in normal and faulty conditions. A Fourier harmonic regression analysis method is applied to determine the confidence intervals for the bearing condition monitoring. The magnitude of harmonics and standard deviation of residuals are analyzed for identifying effect of faults like outer race fault, inner race fault and bearing ball fault. Experimental results show the effectiveness in detection of bearing conditions using the calculations in time domain.

Analysis of growth curves of Guinea fowl (Numida meleagris) fed diets containing dry oregano (Origanum vulgare L.) in an organic system

In this study, 240 day-old guinea fowl ( Numida meleagris ) keets were utilized. They were divided into four treatment groups each containing 20 chicks and were randomly distributed into 12 mobile coops placed in a 100-m2 grazing area. Guinea fowl chicks were randomly allocated to 4 treatment diets containing 0%, 5%, 10%, and 15% dry oregano leaf (DOL) supplements. Nonlinear Gompertz and logistic growth models were used to estimate the mean age-body weight. The growth curve parameters for these models and the following characteristics for fowl were estimated: β0, the asymptotic weight parameter; β1, the scaling parameter; β2, the instantaneous per week growth rate; weight at age of inflection point (WIP); maximum weight gain at inflection point (MWG); and age at the inflection point (AIP). The goodness of fit (GF) for the models was assessed using the following variables: coefficients of determination (r2), mean square error (MSE), adjusted determination coefficient (ADR2), Akaike’s information criteria (AIC), chi-square test (Chi.Sq2) and residual standard deviation (RSD). The different nonlinear function results of the individual data indicated that supplementation of diets with DOL had no significant effects on growth curve parameters when compared with the control diet. Greater correlation values were estimated among β0, β1, β2, WIP, MWG and AIP in the Gompertz equation, and similar results were estimated in the logistic equation, but there was no significant correlation between β2-β1 and β2-MWG. According to the results obtained from the GF, high r2 and ADR2 were estimated in Gompertz and logistic equations (above 0.96).

THE ROLE OF ANALYTICAL APPROACH IN PLANNING OPERATING EXPENSES OF AN ENTERPRISE

Generating economic benefits from the sale of “labor effects” precedes expenses incurrence. The basic criterion for grouping them is a nature of expense method. From the point of view of planning manufacturing processes in an enterprise, it is important to learn about the future expenses estimates, thanks to the use of one of a priori cost accounting systems. The aim of the paper is to review analytical functions for determining the estimated expenses from operating activities, to study the effectiveness thereof against the mechanical approach. The following research theses have been included in the study. Within the analytical approach, due to the non-linearity of the costs by nature, the “good” quality of their “projection” in the depicted enterprise provides a logarithmic curve. Achieving the minimum amount of mean error (ME) of this function in the control area implies the accuracy of the forecast. For the expenses, which are not determined as by nature, satisfactory prediction accuracy appears to be “supplied” by the Holt and Winters models, taking into account possibility of seasonal fluctuations. Each time the distance between the standard deviation of residuals (SE) and the root of mean squared error (MSE) is a necessary condition, whereas the minimization of mean absolute percentage error (MAPE) within the control range a sufficient condition for this fit.

The use of the nonlinear models in the growth of pears of ‘Shinseiki’ cultivar

ABSTRACT: The goal of this study was to elucidate the growth and development of the Asian pear fruit, on the grounds of length, diameter and fresh weight determined over time, using the non-linear Gompertz and Logistic models. The specifications of the models were assessed utilizing the R statistical software, via the least squares method and iterative Gauss-Newton process (DRAPER &amp; SMITH, 2014). The residual standard deviation, adjusted coefficient of determination and the Akaike information criterion were used to compare the models. The residual correlations, observed in the data for length and diameter, were modeled using the second-order regression process to render the residuals independent. The logistic model was highly suitable in demonstrating the data, revealing the Asian pear fruit growth to be sigmoid in shape, showing remarkable development for three variables. It showed an average of up to 125 days for length and diameter and 140 days for fresh fruit weight, with values of 72mm length, 80mm diameter and 224g heavy fat.

Gompertz and Logistic Models to the Productive Traits of Sunn Hemp

Studies on growth models for productive character of sunn hemp are important to know the behavior of the culture. Therefore, the objective of this research was to adjust non-linear models, Gompertz and Logistic, in the description of productive traits of sunn hemp in two sowing periods. Two uniformity trials were performed. The evaluations began on October the 29th 2014 and December the 16th 2014, totaling 94 and 76 evaluation days for periods 1 and 2, respectively. After the emergence of the seeds of sunn hemp, for first period from 7 days after sowing, and from 2 to 13 days after sowing, on each day, they were collected randomly four plants. The traits: fresh matter leaf, stem, root, shoot, and total, and dry matter leaf, stem, root, shoot, and total. For both models the confidence interval was calculated of parameters a, b and c. The adjustment quality of the Gompertz and Logistic models was verified by the determination coefficient, the Akaike information criteria, residual standard deviation, mean absolute deviation, mean absolute percentage error and mean prediction error. The Gompertz model when compared between the sowing periods through the confidence interval of the parameters, for the productive traits, differs. The same result was found for the Logistic model. The growth models of Gompertz and Logistic presented good adjustment quality.

Research on Time Domain Characteristics and Mathematical Model of Electromagnetic Radiation Noise Produced by Single Arc

Current-carrying sliding friction pair is the key part of many systems such as high-speed railway’s pantograph-catenary system, electromagnetic gun’s launch system, and space satellite’s solar panel system. Arc discharge phenomenon will occur due to sliding electrical contact fault. It will radiate high-intensity electromagnetic noise. The electromagnetic radiation noise (EMRN) will disturb communication system, even cause failure of the whole system. EMRN experiments under single arc conditions were carried out with the self-developed experimental system in anechoic chamber environment. The time domain characteristics of EMRN were analyzed under different measure distance and contact current conditions. The time domain waveform of EMRN is symmetrical and convergent. Its continuous time is shorter than 0.8 $\mu \text{s}$ . A mathematical model of the time domain waveform was established by using the least-square method. The performance of the model was evaluated by using determination coefficient, residual standard deviation, and correlation coefficient. The time domain waveform obtained from the model is almost the same as the waveform measured from experiments.

Template-based field map prediction for rapid whole brain B0 shimming.

PurposeIn typical MRI protocols, time is spent acquiring a field map to calculate the shim settings for best image quality. We propose a fast template‐based field map prediction method that yields near‐optimal shims without measuring the field.MethodsThe template‐based prediction method uses prior knowledge of the B0 distribution in the human brain, based on a large database of field maps acquired from different subjects, together with subject‐specific structural information from a quick localizer scan. The shimming performance of using the template‐based prediction is evaluated in comparison to a range of potential fast shimming methods.ResultsStatic B0 shimming based on predicted field maps performed almost as well as shimming based on individually measured field maps. In experimental evaluations at 7 T, the proposed approach yielded a residual field standard deviation in the brain of on average 59 Hz, compared with 50 Hz using measured field maps and 176 Hz using no subject‐specific shim.ConclusionsThis work demonstrates that shimming based on predicted field maps is feasible. The field map prediction accuracy could potentially be further improved by generating the template from a subset of subjects, based on parameters such as head rotation and body mass index. Magn Reson Med 80:171–180, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.