Application of Laplacian-based Methods to Multi-echo Phase Data for Accurate Susceptibility Mapping

In Susceptibility Mapping (SM) using multi-echo gradient-echo phase data, unwrapping and/or background-Òeld removal is often performed using Laplacian-based methods. However, SM pipelines in the literature have applied these methods at di×erent stages. Here, using simulated and acquired images, we compared the performance of three pipelines that apply Laplacian-based methods at di× erent stages. We showed that Laplacian-based methods alter the linearity of the phase over time. We demonstrated that only a processing pipeline that takes this into account, i.e. by Òtting the multi-echo data over time to correctly estimate a Òeld map before applying Laplacian-based methods, gives accurate susceptibility values

Investigating the accuracy and precision of TE‐dependent versus multi‐echo QSM using Laplacian‐based methods at 3 T

Purpose: Multi‐echo gradient‐recalled echo acquisitions for QSM enable optimizing the SNR for several tissue types through multi‐echo (TE) combination or investigating temporal variations in the susceptibility (potentially reflecting tissue microstructure) by calculating one QSM image at each TE (TE‐dependent QSM). In contrast with multi‐echo QSM, applying Laplacian‐based methods (LBMs) for phase unwrapping and background field removal to single TEs could introduce nonlinear temporal variations (independent of tissue microstructure) into the measured susceptibility. Here, we aimed to compare the effect of LBMs on the QSM susceptibilities in TE‐dependent versus multi‐echo QSM. Methods: TE–dependent recalled echo data simulated in a numerical head phantom and gradient‐recalled echo images acquired at 3 T in 10 healthy volunteers. Several QSM pipelines were tested, including four distinct LBMs: sophisticated harmonic artifact reduction for phase data (SHARP), variable‐radius sophisticated harmonic artifact reduction for phase data (V‐SHARP), Laplacian boundary value background field removal (LBV), and one‐step total generalized variation (TGV). Results from distinct pipelines were compared using visual inspection, summary statistics of susceptibility in deep gray matter/white matter/venous regions of interest, and, in the healthy volunteers, regional susceptibility bias analysis and nonparametric tests. Results: Multi‐echo versus TE‐dependent QSM had higher regional accuracy, especially in high‐susceptibility regions and at shorter TEs. Everywhere except in the veins, a processing pipeline incorporating TGV provided the most temporally stable TE‐dependent QSM results with an accuracy similar to multi‐echo QSM. Conclusions: For TE‐dependent QSM, carefully choosing LBMs can minimize the introduction of LBM‐related nonlinear temporal susceptibility variations

open PDS: Protecting the Privacy of Metadata through SafeAnswers.

The rise of smartphones and web services made possible the large-scale collection of personal metadata. Information about individuals' location, phone call logs, or web-searches, is collected and used intensively by organizations and big data researchers. Metadata has however yet to realize its full potential. Privacy and legal concerns, as well as the lack of technical solutions for personal metadata management is preventing metadata from being shared and reconciled under the control of the individual

Investigating the effect of flow compensation and quantitative susceptibility mapping method on the accuracy of venous susceptibility measurement

Quantitative susceptibility mapping (QSM) is a promising non-invasive method for obtaining information relating to oxygen metabolism. However, the optimal acquisition sequence and QSM reconstruction method for reliable venous susceptibility measurements are unknown. Full flow compensation is generally recommended to correct for the influence of venous blood flow, although the effect of flow compensation on the accuracy of venous susceptibility values has not been systematically evaluated. In this study, we investigated the effect of different acquisition sequences, including different flow compensation schemes, and different QSM reconstruction methods on venous susceptibilities. Ten healthy subjects were scanned with five or six distinct QSM sequence designs using monopolar readout gradients and different flow compensation schemes. All data sets were processed using six different QSM pipelines and venous blood susceptibility was evaluated in whole-brain segmentations of the venous vasculature and single veins. The quality of vein segmentations and the accuracy of venous susceptibility values were analyzed and compared between all combinations of sequences and reconstruction methods. The influence of the QSM reconstruction method on average venous susceptibility values was found to be 2.7–11.6 times greater than the influence of the acquisition sequence, including flow compensation. The majority of the investigated QSM reconstruction methods tended to underestimate venous susceptibility values in the vein segmentations that were obtained. In summary, we found that multi-echo gradient-echo acquisition sequences without full flow compensation yielded venous susceptibility values comparable to sequences with full flow compensation. However, the QSM reconstruction method had a great influence on susceptibility values and thus needs to be selected carefully for accurate venous QSM

The strength of the strongest ties in collaborative problem solving

Complex problem solving in science, engineering, and business has become a highly collaborative endeavor. Teams of scientists or engineers collaborate on projects using their social networks to gather new ideas and feedback. Here we bridge the literature on team performance and information networks by studying teams' problem solving abilities as a function of both their within-team networks and their members' extended networks. We show that, while an assigned team's performance is strongly correlated with its networks of expressive and instrumental ties, only the strongest ties in both networks have an effect on performance. Both networks of strong ties explain more of the variance than other factors, such as measured or self-evaluated technical competencies, or the personalities of the team members. In fact, the inclusion of the network of strong ties renders these factors non-significant in the statistical analysis. Our results have consequences for the organization of teams of scientists, engineers, and other knowledge workers tackling today's most complex problems

Quantitative susceptibility mapping (QSM) and R2* of silent cerebral infarcts in sickle cell anemia

Silent cerebral infarction (SCI) is the most commonly reported radiological abnormality in patients with sickle cell anemia (SCA) and is associated with future clinical stroke risk. To date, there have been few histological and quantitative MRI studies of SCI and multiple radiological definitions exist. As a result, the tissue characteristics and composition of SCI remain elusive. The objective of this work was therefore to investigate the composition of segmented SCI lesions using quantitative MRI for R 2 * and quantitative magnetic susceptibility mapping (QSM). 211 SCI lesions were segmented from 32 participants with SCA and 6 controls. SCI were segmented according to two definitions (FLAIR+/-T1w-based threshold) using a semi-automated pipeline. Magnetic susceptibility (χ) and R 2 * maps were calculated from a multi-echo gradient echo sequence and mean SCI values were compared to an equivalent region of interest in normal appearing white matter (NAWM). SCI χ and R 2 * were investigated as a function of SCI definition, patient demographics, anatomical location, and cognition. Compared to NAWM, SCI were significantly less diamagnetic (χ = -0.0067 ppm vs. -0.0153 ppm, p < 0.001) and had significantly lower R 2 * (16.7 s-1 vs. 19.2 s-1, p < 0.001). SCI definition had a significant effect on the mean SCI χ and R 2 * , with lesions becoming significantly less diamagnetic and having significantly lower R 2 * after the application of a more stringent T1w-based threshold. SCI-NAWM R 2 * decrease was significantly greater in patients with SCA compared with controls (-2.84 s-1 vs. -0.64 s-1, p < 0.0001). No significant association was observed between mean SCI-NAWM χ or R2* differences and subject age, lesion anatomical location, or cognition. The increased χ and decreased R 2 * in SCI relative to NAWM observed in both patients and controls is indicative of lower myelin or increased water content within the segmented lesions. The significant SCI-NAWM R 2 * differences observed between SCI in patients with SCA and controls suggests there may be differences in tissue composition relative to NAWM in SCI in the two populations. Quantitative MRI techniques such as QSM and R 2 * mapping can be used to enhance our understanding of the pathophysiology and composition of SCI in patients with SCA as well as controls

Quantitative Susceptibility Mapping (QSM) is Sensitive to Hippocampal and Subcortical Gray Matter Changes in Temporal Lobe Epilepsy

Although temporal lobe epilepsy (TLE) results in widespread changes in MRI measures of tissue volume, diffusion and functional connectivity, changes in tissue composition in TLE have not been investigated with MRI. Quantitative susceptibility mapping (QSM) is sensitive to changes in tissue composition, in particular to iron and myelin. Here, we show for the first time that QSM is sensitive to gray matter abnormalities in 31patients with temporal lobe epilepsy (TLE) compared to 23 healthy controls, and showed significant susceptibility changes in the hippocampus in left TLE patients, and in the bilateral thalamus in both left and right TLE

Evaluating the Accuracy of Susceptibility Maps Calculated from Single-echo versus Multi-echo Gradient-echo Acquisitions

For Susceptibility Mapping (SM), Laplacian-based methods (LBMs) can be used on single- or multi-echo gradient echo phase data. Previous studies have shown the advantage of using multi-echo versus single-echo data for noise reduction in susceptibility-weighted images and simulated data. Here, using simulated and acquired images, we compared the performance of two SM pipelines that used multi- or single-echo phase data and LBMs. We showed that the pipeline that fits the multi-echo data over time first and then applies LBMs gives more accurate local fields and $\chi$ maps than the pipelines that apply LBMs to single-echo phase data

Non-invasive measurement of hepatic venous oxygen saturation (ShvO₂) with quantitative susceptibility mapping in normal mouse liver and livers bearing colorectal metastases

PURPOSE: The purpose of this prospective study was to investigate the potential of QSM to noninvasively measure hepatic venous oxygen saturation (ShvO2). Materials & Methods: All animal studies were performed in accordance with the UK Home Office Animals Science Procedures Act (1986) and UK National Cancer Research Institute (NCRI) guidelines. QSM data was acquired from a cohort of mice (n=10) under both normoxic (medical air, 21% O2/balance N), and hyperoxic conditions (100% O2). Susceptibility measurements were taken from large branches of the portal and hepatic vein under each condition and were used to calculate venous oxygen saturation in each vessel. Blood was extracted from the IVC of three mice under norm- and hyperoxic conditions, and oxygen saturation was measured using a blood gas analyser to act as a gold standard. QSM data was also acquired from a cohort of mice bearing colorectal liver metastases (CRLM). SvO2 was calculated from susceptibility measurements made in the portal and hepatic veins, and compared to the healthy animals. RESULTS: SvO2 calculated from QSM measurements showed a significant increase of 14.93% in the portal vein (p < 0.05), and an increase of 21.39% in the hepatic vein (p < 0.01). Calculated results showed excellent agreement with those from the blood gas analyser (26.14% increase). ShvO2 was significantly lower in the disease cohort (30.18 ± 11.6%), than the healthy animals (52.67 ± 17.8%) (p < 0.05), but differences in the portal vein were not significant. CONCLUSION: QSM is a feasible tool for non-invasively measuring hepatic venous oxygen saturation and can detect differences in oxygen consumption in livers bearing colorectal metastases