Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
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Multicenter Study Comparative Study
Myocardial T2* measurements in iron-overloaded thalassemia: An in vivo study to investigate optimal methods of quantification.
Reproducible and accurate myocardial T2* measurements are required for the quantification of iron in heart tissue in transfused thalassemia. The aim of this study was to determine the best method to measure the myocardial T2* from multi-gradient-echo data acquired both with and without black-blood preparation. Sixteen thalassemia patients from six centers were scanned twice locally, within 1 week, using an optimized bright-blood T2* sequence and then subsequently scanned at the standardization center in London within 4 weeks, using a T2* sequence both with and without black-blood preparation. ⋯ The black-blood data were well fitted by the monoexponential model, which suggests that a more accurate measure of T2* can be obtained by removing the main source of errors in the bright-blood data. For bright-blood data, the offset model appeared to underestimate T2* values substantially and was less reproducible. The truncation model gave rise to more reproducible T2* measurements, which were also closer to the values obtained from the black-blood data.
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Multiecho chemical shift-based water-fat separation methods are seeing increasing clinical use due to their ability to estimate and correct for field inhomogeneities. Previous chemical shift-based water-fat separation methods used a relatively simple signal model that assumes both water and fat have a single resonant frequency. However, it is well known that fat has several spectral peaks. ⋯ The fat spectrum can be assumed to be constant in all subjects and measured a priori using MR spectroscopy. Alternatively, the fat spectrum can be estimated directly from the data using novel spectrum self-calibration algorithms. The improvement in water-fat separation and T(2) (*) estimation is demonstrated in a variety of in vivo applications, including knee, ankle, spine, breast, and abdominal scans.
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The use of spectroscopic Missing Pulse--SSFP (spMP-SSFP) for fast three-dimensional (3D) proton MR spectroscopic imaging (MRSI) at 7 Tesla (T) is demonstrated. Sequence modifications were required regarding the limits of the specific absorption rate as well as hardware limitations with respect to maximum B(1) field strength and B(0) gradient slew rate, as compared to previous studies performed at 3T. The combination of two spatially selective radiofrequency (RF) pulses (with orthogonal slice orientation) and a dual-band chemical shift selective RF pulse for simultaneous water and lipid suppression proved to enable fast 3D MRSI measurements of the brain of healthy volunteers. Using a total measurement time of approximately 8.5 minutes and a nominal and real voxel size of 0.62 cm(3) and 2.6 cm(3), respectively, signals of N-acetyl aspartate, total creatine, choline containing compounds, myo-inositol, and glutamate+glutamine could be detected.