This study demonstrates the applicability of a PD bias correction based on T1 to yield tissue water content at 3T.

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Little information is available on the impact of hemodialysis on cerebral water homeostasis and its distribution in chronic kidney disease. We used a neuropsychological test battery, structural magnetic resonance imaging (MRI) and a novel technique for quantitative measurement of localized water content using 3T MRI to investigate ten hemodialysis patients (HD) on a dialysis-free day and after hemodialysis (2.4±2.2 hours), and a matched healthy control group with the same time interval. Neuropsychological testing revealed mainly attentional and executive cognitive dysfunction in HD. Voxel-based-morphometry showed only marginal alterations in the right inferior medial temporal lobe white matter in HD compared to controls. Marked increases in global brain water content were found in the white matter, specifically in parietal areas, in HD patients compared to controls. Although the global water content in the gray matter did not differ between the two groups, regional increases of brain water content in particular in parieto-temporal gray matter areas were observed in HD patients. No relevant brain hydration changes were revealed before and after hemodialysis. Whereas longer duration of dialysis vintage was associated with increased water content in parieto-temporal-occipital regions, lower intradialytic weight changes were negatively correlated with brain water content in these areas in HD patients. Worse cognitive performance on an attention task correlated with increased hydration in frontal white matter. In conclusion, long-term HD is associated with altered brain tissue water homeostasis mainly in parietal white matter regions, whereas the attentional domain in the cognitive dysfunction profile in HD could be linked to increased frontal white matter water content.

BACKGROUND AND PURPOSE:Hyperattenuated cerebral areas on postinterventional CT are a common finding after endovascular stroke treatment. There is uncertainty about the extent to which these hyperattenuated areas correspond to hemorrhage or contrast agent that extravasated into infarcted parenchyma during angiography. We evaluated whether it is possible to distinguish contrast extravasation from blood on MR imaging.

Purpose Every year, hundreds of people have died and thousands have been injured because of insufficient management of well control at oil and gas drilling and production sites. Major causes which have been reported in previous studies included uncontrollable blowouts and failure of blowout preventers because of insufficient safety practices. These onshore and offshore blowout disasters not only harm the work force but also critically affect the environment and marine life. In this research paper, a detailed quantitative survey and qualitative risk assessments (RA) have been carried out for assessing the potentially hazardous activities associated with well control along with their appropriate controls and risk reduction factors and mitigating measures in Middle East and south East Asian countries. Design/methodology/approach The sequential explanatory research design has been adopted in this study. Whereas, descriptive statistical approach has been used for the quantitative data analysis of this study. While, in-depth interview approach has been used for qualitative data collection. Similarly, what-if analysis method has been adopted in this study for the identification of effective safety and health risk mitigating factors because it provides in-depth information from health and safety environment experts. Findings The cumulative quantitative results based on the response from Saudi Arabian drilling industry have indicated that the well control operation is highly hazardous then Malaysian and Pakistani oil and gas industries. Likewise, findings from what-if analysis approach demonstrate that the drilling crewmembers have repetitively faced life threatening hazards which occur (safety and chemical) during well control onshore and offshore operation because of oil base mud, confined space at site, pinch points and falling during working on blow out preventers. According to the overall result, respondents have highly recommended engineering and administrative hazard controlling factors as most suitable for the elimination of safety and chemical hazards during well control activities. Practical implications Besides, the developed methodological framework for the identification of suitable hazard controls can also be effectively used for potential hazards reorganization and identification of suitable hazard controls for other drilling and production industries and regions for accident prevention and safety and health management. Originality/value This is a first comparative research study which has been carried out in Malaysian, Saudi Arabian and Pakistani onshore and offshore oil and gas industries for well control health and safety management and reorganization of most effective hazards mitigating factors at drilling sites.

Spoiled fast low‐angle shot (FLASH) magnetic resonance imaging (MRI) provides a simple contrast, largely independent of the spin‐spin relaxation time. Three‐dimensional FLASH imaging (3D FLASH) has gained importance due to its simplicity and its ability to produce isotropic, high‐resolution images. Nevertheless, 2D FLASH imaging can be more suited than 3D FLASH imaging in various specific applications requiring long repetition time, such as imaging of the proton density (PD), as it allows interleaved slice acquisition rather than consecutive slice acquisition. In practice, however, a slice‐selective excitation produces a nonuniform excitation profile, which needs to be taken into account to allow reliable quantitative data analysis. In this work, the influence of the nonuniform excitation profile on the detected signal is modeled as a dimensionless multiplicative correction, function of the flip angle, and the ratio of the repetition time to the spin‐lattice relaxation time T1. This model is validated experimentally by measuring the PD and T1 MR parameters in a phantom experiment on a 3T clinical scanner. A good accuracy in the estimation of T1 and in the reconstruction of the PD (weighted by the receiver sensitivity profile) is obtained, for example, a relative error of 3% in T1 within the range [500, 2000] ms and a precision of 1% in PD. It is also shown how the proposed theory can be extended to magnetization‐prepared 2D‐spoiled FLASH as well as other variations of the 2D‐spoiled FLASH sequence. © 2013 Wiley Periodicals, Inc. Concepts Magn Reson Part A 42A: 89–100, 2013.

Water concentration is tightly regulated in the healthy human brain and changes only slightly with age and gender in healthy subjects. Consequently, changes in water content are important for the characterization of disease. MRI can be used to measure changes in brain water content, but as these changes are usually in the low percentage range, highly accurate and precise methods are required for detection. The method proposed here is based on a long-TR (10 s) multiple-echo gradient-echo measurement with an acquisition time of 7:21 min. Using such a long TR ensures that there is no T 1 weighting, meaning that the image intensity at zero echo time is only proportional to the water content, the transmit field, and to the receive field. The receive and transmit corrections, which are increasingly large at higher field strengths and for highly segmented coil arrays, are multiplicative and can be approached heuristically using a bias field correction. The method was tested on 21 healthy volunteers at 3T field strength. Calibration using cerebral-spinal fluid values (∼100% water content) resulted in mean values and standard deviations of the water content distribution in white matter and gray matter of 69.1% (1.7%) and 83.7% (1.2%), respectively. Measured distributions were coil-independent, as seen by using either a 12-channel receiver coil or a 32-channel receiver coil. In a test-retest investigation using 12 scans on one volunteer, the variation in the mean value of water content for different tissue types was ∼0.3% and the mean voxel variability was ∼1%. Robustness against reduced SNR was assessed by comparing results for 5 additional volunteers at 1.5T and 3T. Furthermore, water content distribution in gray matter is investigated and regional contrast reported for the first time. Clinical applicability is illustrated with data from one stroke patient and one brain tumor patient. It is anticipated that this fast, stable, easyto-use, high-quality mapping method will facilitate routine quantitative MR imaging of water content.

A new reconstruction method, coined MIRAGE, is presented for accurate, fast, and robust parameter mapping of multiple-echo gradient-echo (MEGE) imaging, the basis sequence of novel quantitative magnetic resonance imaging techniques such as water content and susceptibility mapping. Assuming that the temporal signal can be modeled as a sum of damped complex exponentials, MIRAGE performs model-based reconstruction of undersampled data by minimizing the rank of local Hankel matrices. It further incorporates multi-channel information and spatial prior knowledge. Finally, the parameter maps are estimated using nonlinear regression. Simulations and retrospective undersampling of phantom and in vivo data affirm robustness, e.g., to strong inhomogeneity of the static magnetic field and partial volume effects. MIRAGE is compared with a state-of-the-art compressed sensing method, -ESPIRiT. Parameter maps estimated from reconstructed data using MIRAGE are shown to be accurate, with the mean absolute error reduced by up to 50% for in vivo results. The proposed method has the potential to improve the diagnostic utility of quantitative imaging techniques that rely on MEGE data.