NeuroImage
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Quantitative susceptibility mapping (QSM) has recently emerged as a novel magnetic resonance imaging (MRI) method to detect non-haem iron deposition, calcifications, demyelination and vascular lesions in the brain. It has been suggested that QSM is more sensitive than the more conventional quantifiable MRI measure, namely the transverse relaxation rate, R2*. Here, we conducted the first high-resolution, whole-brain, simultaneously acquired, comparative study of the two techniques using 7Tesla MRI. ⋯ QSM, however, provided superior anatomical contrast and revealed age-related differences in the thalamus and in white matter, which were otherwise largely undetected by R2* measurements. In contrast, in occipital cortex, age-related differences were much greater with R2* compared to QSM. The present study, therefore, demonstrated that in vivo QSM using ultra-high field MRI provides a novel means to characterise age-related differences in the human brain, but also combining QSM and R2* using multi-gradient recalled echo imaging can potentially provide a more complete picture of mineralisation, demyelination and/or vascular alterations in aging and disease.
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In multi-shot diffusion imaging, motion induced phase variations are traditionally seen as a source of artifacts and corrected in the image domain using SENSE-based methods. This correction usually requires image echo and navigator echo to be geometrically matched. Recently, a k-space based method, realigned GRAPPA, has been proposed. ⋯ Then a compact kernel is used which only includes acquired data with significant contribution for the data synthesis, and can generate accurate weights without strict navigator size requirements. Simulation studies as well as brain and cervical spine experiments demonstrate that the proposed reconstruction method can effectively suppress artifacts caused by phase variations, and provide diffusion images with high resolution and low distortion. Compared with SENSE-based methods, the proposed method is less sensitive to mismatch between image echo and navigator echo.