Spatial two tissue compartment model for DCE-MRI

In the quantitative analysis of Dynamic Contrast-Enhanced Magnetic Resonance Imaging (DCE-MRI) compartment models allow to describe the uptake of contrast medium with biological meaningful kinetic parameters. As simple models often fail to adequately describe the observed uptake behavior, more complex compartment models have been proposed. However, the nonlinear regression problem arising from more complex compartment models often suffers from parameter redundancy. In this paper, we incorporate spatial smoothness on the kinetic parameters of a two tissue compartment model by imposing Gaussian Markov random field priors on them. We analyse to what extent this spatial regularisation helps to avoid parameter redundancy and to obtain stable parameter estimates. Choosing a full Bayesian approach, we obtain posteriors and point estimates running Markov Chain Monte Carlo simulations. The proposed approach is evaluated for simulated concentration time curves as well as for in vivo data from a breast cancer study

Relation between high-sensitivity C-reactive protein and cardiovascular and renal markers in a middle-income country in the African region.

BACKGROUND: High-sensitivity C-reactive protein (hs-CRP) is associated with several cardiovascular risk factors (CVRF) and with renal function markers. However, these associations have not been examined in populations in the African region. We analyzed the distribution of hs-CRP and the relationship with a broad set of CVRF, renal markers and carotid intima-media thickness (IMT), in the Seychelles (African region). METHODS: We conducted a survey in the population aged 25-64years (n=1255, participation rate: 80.2%). Analyses were restricted to persons of predominantly African descent (n=1011). RESULTS: Mean and median hs-CRP serum concentrations (mg/l) were 3.1 (SD 7.6) and 1.4 (IQR 0.7-2.9) in men and 4.5 (SD 6.7) and 2.2 (IQR 1.0-5.4) in women (p<0.001 for difference between men and women). hs-CRP was significantly associated with several conventional CVRF, and particularly strongly with markers of adiposity. With regards to renal markers, hs-CRP was strongly associated with cystatin C and with microalbuminuria but not with creatinine. hs-CRP was not associated with IMT. CONCLUSIONS: Serum concentration of hs-CRP was significantly associated with sex, several CVRF and selected renal function markers, which extends similar findings in Europe and in North America to a population in the African region. These findings can contribute to guide recommendations for the use of hs-CRP in clinical practice in the region

Multi‐system repeatability and reproducibility of apparent diffusion coefficient measurement using an ice‐water phantom

Purpose: To determine quantitative quality control procedures to evaluate technical variability in multi‐center measurements of the diffusion coefficient of water as a prerequisite to use of the biomarker apparent diffusion coefficient (ADC) in multi‐center clinical trials. Materials and Methods: A uniform data acquisition protocol was developed and shared with 18 participating test sites along with a temperature‐controlled diffusion phantom delivered to each site. Usable diffusion weighted imaging data of ice water at five b‐values were collected on 35 clinical MRI systems from three vendors at two field strengths (1.5 and 3 Tesla [T]) and analyzed at a central processing site. Results: Standard deviation of bore‐center ADCs measured across 35 scanners was 10%) vendor‐specific and system‐specific spatial nonuniformity ADC bias was detected for the off‐center measurement that was consistent with gradient nonlinearity. Conclusion: Standardization of DWI protocol has improved reproducibility of ADC measurements and allowed identifying spatial ADC nonuniformity as a source of error in multi‐site clinical studies. J. Magn. Reson. Imaging 2013;37:1238–1246. © 2012 Wiley Periodicals, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97442/1/23825_ftp.pd

Об анатомическом строении членистостебельного растения Annulina Neuburgiana Radczenko

The purpose was to compare two approaches for the acquisition and analysis of dynamic-contrast-enhanced MRI data with respect to differences in the modelling of the arterial input-function (AIF), the dependency of the model parameters on physiological parameters and their numerical stability. Eight hundred tissue concentration curves were simulated for different combinations of perfusion, permeability, interstitial volume and plasma volume based on two measured AIFs and analysed according to the two commonly used approaches. The transfer constants (Approach 1) K (trans) and (Approach 2) k (ep) were correlated with all tissue parameters. K (trans) showed a stronger dependency on perfusion, and k (ep) on permeability. The volume parameters (Approach 1) v (e) and (Approach 2) A were mainly influenced by the interstitial and plasma volume. Both approaches allow only rough characterisation of tissue microcirculation and microvasculature. Approach 2 seems to be somewhat more robust than 1, mainly due to the different methods of CA administration

Influence of B1 Inhomogeneity on Pharmacokinetic Modeling of Dynamic Contrast-Enhanced MRI: A Simulation Study

Objective: To simulate the B1-inhomogeneity-induced variation of pharmacokinetic parameters on DCE-MRI. Materials and Methods: B1-inhomogeneity-induced flip angle (FA) variation was estimated in a phantom study. Monte Carlo simulation was performed to assess the FA-deviation-induced measurement error of the pre-contrast R1, contrast-enhancement ratio, Gd concentration, and two-compartment pharmacokinetic parameters (Ktrans, ve and vp). Results: B1-inhomogeneity resulted in -23% ~ 5% fluctuations (95% confidence interval (CI) of % error) of FA. The 95% CIs of FA-dependent % errors in the gray matter and blood were as follows: -16.7% - 61.8% and -16.7% - 61.8% for the pre-contrast R1, -1.0% - 0.3% and -5.2% - 1.3% for the contrast-enhancement ratio, and -14.2% - 58.1% and -14.1% - 57.8% for the Gd concentration, respectively. These resulted in -43.1% - 48.4% error for Ktrans, -32.3% - 48.6% error for the ve, and -43.2% - 48.6% error for vp. The pre-contrast R1 was more vulnerable to FA error than the contrast-enhancement ratio, and was therefore a significant cause of the Gd-concentration error. For example, a -10% FA error led to a 23.6% deviation in the pre-contrast R1, -0.4% in the contrast-enhancement ratio, and 23.6% in the Gd concentration. In a simulated condition with a 3% FA error in a target lesion and a -10% FA error in a feeding vessel, the % errors of the pharmacokinetic parameters were -23.7% for Ktrans, -23.7% for ve, and -23.7% for vp. Conclusion: Even a small degree of B1-inhomogeneity can cause a significant error in the measurement of pharmacokinetic parameters on DCE-MRI, while the vulnerability of the pre-contrast R1 calculations to FA deviations is a significant cause of the miscalculation.ope

On the Existence of Solutions to the Muskat Problem With Surface Tension

We consider the Muskat Problem with surface tension in two dimensions over the real line, with $H^{s}$ initial data and allowing the two fluids to have different constant densities and viscosities. We take the angle between the interface and the horizontal, and derive an evolution equation for it. We use energy methods to prove that a solution $\theta$ exists locally and can be continued while $||\theta||_{s}$ remains bounded and the arc chord condition holds. Furthermore, the resulting solution is unique, and depends continuously on the initial data. Additionally, when both fluids have the same viscosity and the initial data is sufficiently small, we show the energy is non-increasing, and that the solution $\theta$ exists globally in time

On the assembly of a grassland plant community

The species pool for a site is defined as that set of species which have a non-zero probability of maintaining viable populations under the prevailing environmental conditions. it may contain many more species than are actually present in the community of the site. The science of community assembly attempts to understand how particular communities arise from the welter of possible species combinations. The assembly of a grassland plant community from the local species pool was examined in a phylogenetically corrected trait-based study. Competition theory suggests coexisting species should be less similar than expected by chance, whilst environmental sorting theory suggests they should be more similar. This work suggests that, at the whole community scale, species tend to be more similar and that their likelihood of occurrence in communities can to an extent be predicted from their traits. Experimental studies revealed a complicated picture. Species naturally occurring in the community did not show convincing signs of outperforming their absent congeners. Community composition appears to depend in considerable measure upon chance events such as seed dispersal coinciding with the availability of vacant microsites in the community, rather than just a sorting process in which the best suited species are invariably present. These findings suggest that it modelling community assembly is possible, but that it is unlikely ever to be an exact science because it is influenced to a large extent by unpredictable events

Estimate of vascular permeability and cerebral blood volume using Gd-DTPA contrast enhancement and dynamic T2*-weighted MRI

Purpose To develop a numerical approach for estimation of vascular permeability from dynamic T2*-weighted imaging, a technique routinely used to measure cerebral blood volume (CBV) and flow in gliomas. Materials and Methods This study describes a process for estimating both the gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) transvascular transfer constant and CBV from dynamic T2*-weighted images. The algorithm was applied to data from the brains of 12 patients with grade IV gliomas. The stability of the method was assessed. Estimates of CBV by this technique were compared to those of the conventional method. Results The algorithm was found to be insensitive to noise and to generate stable voxel-by-voxel estimates of permeability and CBV. Conclusion Using a single imaging acquisition, the three most important vascular properties, CBV, cerebral blood flow (CBF), and permeability, can be estimated. This approach may have potential in clinical evaluation of patients with brain tumor or acute ischemic stroke. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/55796/1/20634_ftp.pd