The quantification of sodium MR images from an arbitrary intensity scale into a bioscale fosters image interpretation in terms of the spatially resolved biochemical process of sodium ion homeostasis. A methodology for quantifying tissue sodium concentration using a flexible twisted projection imaging sequence is proposed that allows for optimization of tradeoffs between readout time, signal-to-noise ratio efficiency, and sensitivity to static field susceptibility artifacts. The gradient amplitude supported by the slew rate at each k-space radius regularizes the readout gradient waveform design to avoid slew rate violation. Static field inhomogeneity artifacts are corrected using a frequency-segmented conjugate phase reconstruction approach, with field maps obtained quickly from coregistered proton imaging. High-quality quantitative sodium images have been achieved in phantom and volunteer studies with real isotropic spatial resolution of 7.5 3 7.5 3 7.5 mm 3 for the slow T 2 component in~8 min on a clinical 3-T scanner. After correcting for coil sensitivity inhomogeneity and water fraction, the tissue sodium concentration in gray matter and white matter was measured to be 36.6 6 0.6 mmol/g wet weight and 27.6 6 1.2 mmol/g wet weight, respectively. Magn Reson Med 63:1583-1593, 2010. V C 2010 Wiley-Liss, Inc. Key words: sodium imaging; twisted projection imaging; quantitative imaging; tissue sodium concentration; ultra-short TE imagingRegulation of sodium homeostasis through counterbalancing low intracellular and high extracellular sodium ion concentrations with potassium ions is of vital importance for cellular function (1,2). These ion gradients across the cell membrane provide the potential energy for many important cellular transport processes. Action potentials, intracellular pH regulation, and many membrane transport processes are all directly dependent on the sodium ion gradient across the cell membrane. Damage to brain cell integrity and disruption of cell packing produce local increases in tissue sodium concentration (TSC) (3,4). TSC, determined by quantitative MRI, has been shown to have a potential role in monitoring tissue viability in humans with diseases such as stroke and in monitoring treatment of brain tumors (3-6).Despite these potential medical applications described more than two decades ago (7), quantitative sodium imaging has been slow to evolve. The sodium MR signal has a detection sensitivity of four orders of magnitude lower than that of the proton signal. It exhibits biexponential relaxation behavior with fast and slow transverse relaxation characteristics (T 2fast $1-3 ms and T 2slow $12-25 ms, respectively) in biologic tissues (8). Therefore, sodium imaging requires an imaging sequence with a short excitation radiofrequency (RF) pulse and a short echo time (TE) to reduce signal loss from the rapid decay of the transverse magnetization.Twisted projection imaging (TPI) is a three-dimensional (3D) projection reconstruction sequence-based approach that can achieve short TE values and high a...

).q RSNA, 2015 Purpose:To demonstrate that a new set of parameters (D, b, and m) from a fractional order calculus (FROC) diffusion model can be used to improve the accuracy of MR imaging for differentiating among low-and high-grade pediatric brain tumors. Materials and Methods:The institutional review board of the performing hospital approved this study, and written informed consent was obtained from the legal guardians of pediatric patients. Multi-b-value diffusion-weighted magnetic resonance (MR) imaging was performed in 67 pediatric patients with brain tumors. Diffusion coefficient D, fractional order parameter b (which correlates with tissue heterogeneity), and a microstructural quantity m were calculated by fitting the multi-b-value diffusion-weighted images to an FROC model. D, b, and m values were measured in solid tumor regions, as well as in normal-appearing gray matter as a control. These values were compared between the lowand high-grade tumor groups by using the Mann-Whitney U test. The performance of FROC parameters for differentiating among patient groups was evaluated with receiver operating characteristic (ROC) analysis. Results:None of the FROC parameters exhibited significant differences in normal-appearing gray matter (P  .24), but all showed a significant difference (P , . Conclusion:The FROC parameters can be used to differentiate between low-and high-grade pediatric brain tumor groups. The combination of FROC parameters or individual parameters may serve as in vivo, noninvasive, and quantitative imaging markers for classifying pediatric brain tumors.q RSNA, 2015

Mapping anatomical brain networks with graph-theoretic analysis of diffusion tractography has recently gained popularity, because of its presumed value in understanding brain function. However, this approach has seldom been used to compare brain connectomes across species, which may provide insights into brain evolution. Here, we employed a data-driven approach to compare interregional brain connections across three primate species: 1) the intensively studied rhesus macaque, 2) our closest living primate relative, the chimpanzee, and 3) humans. Specifically, we first used random parcellations and surface-based probabilistic diffusion tractography to derive the brain networks of the three species under various network densities and resolutions. We then compared the characteristics of the networks using graph-theoretic measures. In rhesus macaques, our tractography-defined hubs showed reasonable overlap with hubs previously identified using anterograde and retrograde tracer data. Across all three species, hubs were largely symmetric in the two hemispheres and were consistently identified in medial parietal, insular, retrosplenial cingulate and ventrolateral prefrontal cortices, suggesting a conserved structural architecture within these regions. However, species differences were observed in the inferior parietal cortex, polar and medial prefrontal cortices. The potential significance of these interspecies differences is discussed.

Background Dilated brain perivascular spaces (PVSs) are found to be associated with many conditions, including aging, dementia, and Alzheimer's disease (AD). Conventionally, PVS assessment is mainly based on subjective observations of the number, size and shape of PVSs in MR images collected at clinical field strengths (≤ 3T). This study tests the feasibility of imaging and quantifying brain PVS with an ultrahigh 7T whole-body MRI scanner. New Method 3D high resolution T2-weighted brain images from healthy subjects (n=3) and AD patients (n=5) were acquired on a 7T whole-body MRI scanner. To automatically segment the small hyperintensive fluid-filling PVS structures, we also developed a quantitative program based on algorithms for spatial gradient, component connectivity, edge-detection, k-means clustering, etc, producing quantitative results of white matter PVS volume densities. Results The 3D maps of automatically segmented PVS show an apparent increase in PVS density in AD patients compared to age-matched healthy controls due to the PVS dilation (8.0 ± 2.1 v/v% in AD vs. 4.9 ± 1.3% in controls, p<0.05). Comparison with Existing Method We demonstrated that 7T provides sufficient SNR and resolution for quantitatively measuring PVSs in deep white matter that is challenging with clinical MRI systems (≤ 3T). Compared to the conventional visual counting and rating for the PVS assessment, the quantitation method we developed is automatic and objective. Conclusions Quantitative PVS MRI at 7T may serve as a non-invasive and endogenous imaging biomarker for diseases with PVS dilation.