Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
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Magnetic resonance imaging (MRI) near metallic implants remains an unmet need because of severe artifacts, which mainly stem from large metal-induced field inhomogeneities. This work addresses MRI near metallic implants with an innovative imaging technique called "Slice Encoding for Metal Artifact Correction" (SEMAC). The SEMAC technique corrects metal artifacts via robust encoding of each excited slice against metal-induced field inhomogeneities. ⋯ By positioning all spins in a region-of-interest to their actual spatial locations, the through-plane distortions can be corrected by summing up the resolved spins in each voxel. The SEMAC technique does not require additional hardware and can be deployed to the large installed base of whole-body MRI systems. The efficacy of the SEMAC technique in eliminating metal-induced distortions with feasible scan times is validated in phantom and in vivo spine and knee studies.
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Dynamic susceptibility contrast MRI (DSC-MRI) is the current standard for the measurement of Cerebral Blood Flow (CBF) and Cerebral Blood Volume (CBV), but it is not suitable for the measurement of Extraction Flow (EF) and may not allow for absolute quantification. The objective of this study was to develop and evaluate a methodology to measure CBF, CBV, and EF from T1-weighted dynamic contrast-enhanced MRI (DCE-MRI). A two-compartment modeling approach was developed, which applies both to tissues with an intact and with a broken Blood-Brain-Barrier (BBB). ⋯ The model provides a consistent description of tracer kinetics in all brain tissues, and an accurate assessment of perfusion and permeability in reference tissues. The measurement sequence requires optimization to improve CNR and the precision in the perfusion parameters. With this approach, DCE-MRI presents a promising alternative to DSC-MRI for quantitative bolus-tracking in the brain.
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To improve the reproducibility of arterial input function (AIF) registration and absolute cerebral blood flow (CBF) quantification in dynamic-susceptibility MRI-perfusion (MRP) at 1.5T, we rescaled the AIF by use of a venous output function (VOF). We compared CBF estimates of 20 healthy, elderly volunteers, obtained by computed tomography (CT)-perfusion (CTP) and MRP on two consecutive days. ⋯ The rescaled MRP showed fair to moderate correlation with CTP for the central gray matter (GM) and the whole brain. Our results indicate that the method used for correction of partial volume effects (PVEs) improves MRP experiments by reducing AIF-introduced variance at 1.5T.
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Quantitative abdominal T(2) measurements may be useful for lesion differentiation and functional tissue characterization. However, T(2) mapping of the abdomen with conventional spin-echo (SE) and turbo-spin-echo (TSE) approaches can be challenging due to physiologic motion artifacts. ⋯ With echo-reordering to accurately estimate effective echo times and an extended slice thickness ratio to reduce stimulated echo effects, a modified PROPELLER approach may permit accurate, robust abdominal T(2) measurements. We validated the accuracy of our modified PROPELLER T(2)-mapping approach by comparison to conventional SE measurements in a phantom model and demonstrated the feasibility of acquiring accurate, high-quality abdominal T(2) maps in normal volunteers.
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For non-Cartesian data acquisition in MRI, k-space trajectory infidelity due to eddy current effects and other hardware imperfections will blur and distort the reconstructed images. Even with the shielded gradients and eddy current compensation techniques of current scanners, the deviation between the actual k-space trajectory and the requested trajectory remains a major reason for image artifacts in non-Cartesian MRI. It is often not practical to measure the k-space trajectory for each imaging slice. ⋯ Then a novel estimation method combining the anisotropic delay model and a simple convolution eddy current model further reduces the artifact level in spiral image reconstruction. The root mean square error and peak error in both phantom and in vivo images reconstructed using the estimated trajectories are reduced substantially compared to the results achieved by only tuning delays. After a one-time calibration, it is thus possible to get an accurate estimate of the spiral trajectory and a high-quality image reconstruction for an arbitrary scan plane.