Rapid measurement of intravoxel incoherent motion (IVIM) derived perfusion fraction for clinical magnetic resonance imaging

Objective This study aimed to investigate the reliability of intravoxel incoherent motion (IVIM) model derived parameters D and f and their dependence on b value distributions with a rapid three b value acquisition protocol. Materials and methods Diffusion models for brain, kidney, and liver were assessed for bias, error, and reproducibility for the estimated IVIM parameters using b values 0 and 1000, and a b value between 200 and 900, at signal-to-noise ratios (SNR) 40, 55, and 80. Relative errors were used to estimate optimal b value distributions for each tissue scenario. Sixteen volunteers underwent brain DW-MRI, for which bias and coefficient of variation were determined in the grey matter. Results Bias had a large influence in the estimation of D and f for the low-perfused brain model, particularly at lower b values, with the same trends being confirmed by in vivo imaging. Significant differences were demonstrated in vivo for estimation of D (P = 0.029) and f (P < 0.001) with [300,1000] and [500,1000] distributions. The effect of bias was considerably lower for the high-perfused models. The optimal b value distributions were estimated to be brain500,1000, kidney300,1000, and liver200,1000. Conclusion IVIM parameters can be estimated using a rapid DW-MRI protocol, where the optimal b value distribution depends on tissue characteristics and compromise between bias and variability

GliMR: Cross-Border Collaborations to Promote Advanced MRI Biomarkers for Glioma

Purpose: There is an annual incidence of 50,000 glioma cases in Europe. The optimal treatment strategy is highly personalised, depending on tumour type, grade, spatial localization, and the degree of tissue infiltration. In research settings, advanced magnetic resonance imaging (MRI) has shown great promise as a tool to inform personalised treatment decisions. However, the use of advanced MRI in clinical practice rem

The structure of human parathyroid hormone from a study of fragments in solution using 1H NMR spectroscopy and its biological implications

In order to gain insight into the structure of human parathyroid hormone (hPTH), four fragments [hPTH(1-34), hPTH(18-48), hPTH(28-48), and hPTH(53-84)], which cover all regions of the intact hormone, have been investigated by CD and NMR spectroscopy in combination with distance geometry, and restrained molecular dynamics and energy minimization calculations, under a variety of solution conditions. Significantly, all fragments showed little propensity to form stable structures in aqueous solution alone, and it was only on the addition of trifluoroethanol (TFE) that defined structural features were observed. In an extension of earlier work [Klaus et al. (1991) Biochemistry 30, 6936-6942], hPTH(1-34) in 70% trifluoroethanol (TFE) showed two helices that were longer than in 10% TFE, but essentially showed the same characteristics. Although overlap in the 1H NMR spectra prevented the determination of quantitative NOE data for residues 26-30, the combination of the alpha-proton chemical shift data and quantitative NOE data indicated the helices extend from residues 3 to 13 and 15 to 29. No evidence was found for interaction of the two helical regions. The nature and extent of this second helix in the intact hormone were better defined from the data for hPTH(18-48). Under limiting solution conditions, where the fragment assumed its maximum helical content, a well-defined helix was observed between residues 21 and 38 with a possible discontinuity between Leu-28 and Gln-29. There was little evidence of any form of secondary structure between Gly-38 and the terminus of this fragment, Ser-48. In keeping with this result, the shorter fragment, hPTH(28-48), showed little evidence of stable secondary structure on addition of TFE. From the alpha-proton chemical shifts residues 23-27 appeared to sustain helical structure more readily than the rest of molecule under all solution regimes in both hPTH(1-34) and hPTH(18-48). In contrast to the other two longer fragments hPTH(53-84) showed little propensity for helical secondary structure even at the highest TFE concentrations. However, there was evidence that the molecule did adopt a defined three-dimensional structure. Various long-range NOE's were observed in 10% TFE that allowed the calculation of an open tertiary structure consisting of an initial series of turns surrounded by a loop structure of several loose turn

On probing intravoxel incoherent motion in the heart‐spin‐echo versus stimulated‐echo DWI

Purpose: Mapping intravoxel incoherent motion (IVIM) in the heart remains challenging despite advances in cardiac DWI and DTI. In the present work, simulations and experimental imaging are used to compare the IVIM encoding efficiency of spin-echo- and stimulated-echo-based DWI/DTI for assessing myocardial perfusion. Methods: Using normalized phase distributions and statistical models of capillary networks derived from histological studies, along with typical diffusion gradient waveforms for in vivo cardiac DWI/DTI, Monte Carlo simulations were performed. The simulation results were compared to IVIM measurements of perfused porcine hearts regarding both magnitude and phase modulation. An IVIM tensor model was used to account for anisotropy of the capillary network, and potential bias of parameter estimation was reported based on simulations. Results: Both computer simulations and experimental data demonstrate a low sensitivity of spin-echo DWI/DTI sequences for IVIM parameters, whereas stimulated-echo-based DWI/DTI with typical mixing times can differentiate between no-flow baseline and perfused myocardium (+129% IVIM-derived flow). In addition, ischemic territories induced by coronary occlusion could be successfully detected. With increasing order of motion compensation (M0/M1/M2) of the diffusion encoding gradients, as required for cardiac in vivo spin-echo DWI/DTI, the low IVIM sensitivity of spin-echo DWI/DTI decreased further in simulations: maximum attenuations of perfusion compartment 52/13/5% (b = 500 s/mm2 ). Conclusion: Given the short encoding time of spin-echo-based DWI/DTI sequences, a limited perfusion sensitivity results, in particular in combination with motion-compensated diffusion gradients. In contrast, stimulated-echo based DWI/DTI has the potential to identify perfusion changes in cardiac IVIM in vivo

Enhancing intravoxel incoherent motion parameter mapping in the brain using k-b PCA

Intravoxel incoherent motion (IVIM) imaging of diffusion and perfusion parameters in the brain using parallel imaging suffers from local noise amplification. To address the issue, signal correlations in space and along the diffusion encoding dimension are exploited jointly using a constrained image reconstruction approach. IVIM imaging was performed on a clinical 3 T MR system with diffusion weighting along six gradient directions and 16 b‐values encoded per direction across a range of 0–900 s/mm2. Data were collected in 11 subjects, retrospectively undersampled in k‐space with net factors ranging from 2 to 6 and reconstructed using CG‐SENSE and the proposed k‐b PCA approach. Results of k‐b PCA and CG‐SENSE from retrospectively undersampled data were compared with those from the fully sampled reference. In addition, prospective single‐shot k‐b undersampling was implemented and data were acquired in five additional volunteers. IVIM parameter maps were derived using a segmented least‐squares method. The proposed k‐b PCA method outperformed CG‐SENSE in terms of reconstruction errors for effective undersampling factors of 3 and beyond. Undersampling artifacts were effectively removed with k‐b PCA up to sixfold undersampling. At net sixfold undersampling, relative errors (compared with the fully sampled reference) of image magnitude and IVIM parameters (D, f and D*) were (median ± interquartile range): 3.5 ± 3.7 versus 25.3 ± 25.8%, 2.7 ± 3.6 versus 14.2 ± 20.4%, 15.1 ± 26.1 versus 96.6 ± 67.4% and 14.8 ± 26.6 versus 100 ± 195.1% for k‐b PCA versus CG‐SENSE, respectively. Acquisition with sixfold prospective undersampling yielded average IVIM parameters in the brain of 0.79 ± 0.18 × 10−3 mm2/s for D, 7.35 ± 7.27% for f and 7.11 ± 2.39 × 10−3 mm2/s for D*. Constrained reconstruction using k‐b PCA improves IVIM parameter mapping from undersampled data when compared with CG‐SENSE reconstruction. Prospectively undersampled single‐shot echo planar imaging acquisition was successfully employed using k‐b PCA, demonstrating a reduction of image artifacts and noise relative to parallel imaging