Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
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Three-dimensional spin-lattice relaxation time in the rotating frame (3D-T1rho) with parallel imaging at 3.0T was implemented on a whole-body clinical scanner. A 3D gradient-echo sequence with a self-compensating spin-lock pulse cluster was combined with generalized autocalibrating partially parallel acquisitions (GRAPPA) to acquire T1rho-weighted images. 3D-T1rho maps of an agarose phantom and three healthy subjects were constructed using an eight-channel phased-array coil without parallel imaging and with parallel imaging acceleration factors of 2 and 3, in order to assess the reproducibility of the method. The coefficient of variation (CV) of the median T1rho of the agarose phantom was 0.44%, which shows excellent reproducibility. ⋯ The CV of the median T1rho of the patellar cartilage varied between approximately 1.1% and 4.3%. Similarly, the CV varied between approximately 2.1-5.8%, approximately 1.4-8.7%, and approximately 1.5-4.1% for the biceps femoris and lateral and medial gastrocnemius muscles, respectively. The preliminary results demonstrate that 3D-T1rho maps can be constructed with good reproducibility using parallel imaging. 3D-T1rho with parallel imaging capability is an important clinical tool for reducing both the total acquisition time and RF energy deposition at 3T.
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Viability detection is crucial for the management of myocardial infarction (MI). Signal intensity (SI)-based MRI methods may overestimate infarct size in vivo. In contrast to SI, the longitudinal relaxation-rate enhancement (DeltaR1) is an intrinsic parameter that is linearly proportional to the concentration of contrast agent (CA). ⋯ Median deviations from the true infarction fraction (IF) were 1.23% and 0.49% of LV at 24 hr and 48 hr, respectively. No significant difference was found between PIM24 hr and PIM48 hr. DeltaR1-based PIM is an accurate and reproducible method for quantifying myocardial viability distribution, and thus enhances the clinical utility of CE-MRI.
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Arterial spin labeling (ASL) MRI is a useful technique for noninvasive measurement of cerebral blood flow (CBF) in humans. High field strength provides a unique advantage for ASL because of longer blood T(1) relaxation times, making this technique a promising quantitative approach for functional brain mapping. However, higher magnetic field also introduces new challenges. ⋯ If not accounted for, such an effect can complicate the interpretation of the ASL results, e.g., causing a delayed onset and offset of the response, or inducing an artifactual poststimulus undershoot. The BOLD contribution also decreases the sensitivity of ASL-based fMRI. Correction methods are proposed to reduce the artifact, giving increased number of activated voxels (18+/-5%, P=0.006) and more accurate estimation of CBF temporal characteristics.
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Comparative Study
Comparison of errors associated with single- and multi-bolus injection protocols in low-temporal-resolution dynamic contrast-enhanced tracer kinetic analysis.
Accurate sampling of the arterial input function (AIF) in low-temporal-resolution quantitative dynamic contrast-enhanced MRI (DCE-MRI) studies is crucial for accurate and reproducible parameter estimation. However, when conventional AIFs are sampled at low temporal resolution, they introduce an unpredictable degree of error. ⋯ A range of tissue uptake curves for each AIF form were generated using a distributed parameter model, and Monte Carlo simulation studies were performed over a range of offset times (to mimic temporal mis-sampling), temporal resolutions and SNR in order to compare the performance of both AIF forms in compartmental modeling. Insufficient data sampling of the single bolus AIF at temporal resolutions in excess of 9 s leads to large errors, which can be reduced by employing an additional, appropriately administered, second CA bolus injection.
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The shells trajectory is a 3D data acquisition method with improved efficiency compared to Cartesian sampling. It is a true center-out trajectory that does not repeatedly resample the center of k-space, and also offers advantages for motion correction. This work demonstrates that k-space undersampling can be combined with the shells trajectory to further accelerate the acquisition. ⋯ Various undersampling schemes with different beta values were examined. Phantom and volunteer studies demonstrate that when up to a twofold acceleration is achieved, only minor artifacts are introduced by undersampling the shells trajectory. For a fixed acquisition time, the improved efficiency can be used to increase spatial resolution.