To compare accuracy, precision, and reproducibility of four commonly used myocardial T1 mapping sequences: modified Look-Locker inversion recovery (MOLLI), shortened MOLLI (ShMOLLI), saturation recovery single-shot acquisition (SASHA), and saturation pulse prepared heart rate independent inversion recovery (SAPPHIRE). Materials andMethods:This HIPAA-compliant study was approved by the institutional review board. All subjects provided written informed consent. Accuracy, precision, and reproducibility of the four T1 mapping sequences were first compared in phantom experiments. In vivo analysis was performed in seven healthy subjects (mean age 6 standard deviation, 38 years 6 19; four men, three women) who were imaged twice on two separate days. In vivo reproducibility of native T1 mapping and extracellular volume (ECV) were measured. Differences between the sequences were assessed by using Kruskal-Wallis and Wilcoxon rank sum tests (phantom data) and mixed-effect models (in vivo data). Results:T1 mapping accuracy in phantoms was lower with ShMOLLI (62 msec) and MOLLI (44 msec) than with SASHA (13 msec; P , .05) and SAPPHIRE (12 msec; P , .05). MOLLI had similar precision to ShMOLLI (4.0 msec vs 5.6 msec; P = .07) but higher precision than SAPPHIRE (6.8 msec; P = .002) and SASHA (8.7 msec; P , .001). All sequences had similar reproducibility in phantoms (P = .1). The four sequences had similar in vivo reproducibility for native T1 mapping (~25-50 msec; P . .05) and ECV quantification (~0.01-0.02; P . .05). Conclusion:SASHA and SAPPHIRE yield higher accuracy, lower precision, and similar reproducibility compared with MOLLI and ShMOLLI for T1 measurement. Different sequences yield different ECV values; however, all sequences have similar reproducibility for ECV quantification.q RSNA, 2014

The STONE sequence allows accurate and precise quantification of native myocardial T times with the additional benefit of covering the entire ventricle. Magn Reson Med 74:115-124, 2015. © 2014 Wiley Periodicals, Inc.

The use of proton resonance frequency shift-based magnetic resonance (MR) thermometry for interventional guidance on abdominal organs is hampered by the constant displacement of the target due to the respiratory cycle and the associated thermometry artifacts. Ideally, a suitable MR thermometry method should for this role achieve a subsecond temporal resolution while maintaining a precision comparable to those achieved on static organs while not introducing significant processing latencies. Here, a computationally effective processing pipeline for two-dimensional image registration coupled with a multibaseline phase correction is proposed in conjunction with high-frame-rate MRI as a possible solution. The proposed MR thermometry method was evaluated for 5 min at a frame rate of 10 images/sec in the liver and the kidney of 11 healthy volunteers and achieved a precision of less than 2°C in 70% of the pixels while delivering temperature and thermal dose maps on the fly. The ability to perform MR thermometry and dosimetry in vivo during a real intervention was demonstrated on a porcine kidney during a high-intensity focused ultrasound heating experiment. Magn Reson Med 63:1080-1087, 2010. V C 2010 Wiley-Liss, Inc. Key words: MRI; thermometry; temperature; interventional; imaging; real time system; motion artifacts; proton resonance frequency shift; PRF MR thermometry relying on the water proton resonance frequency is gaining importance for monitoring and guiding thermal therapies such as radiofrequency (1), laser (2), or focused ultrasound thermal ablation (3-5). Typically, proton resonance frequency-based MR thermometry relies on the voxelwise evaluation of phase differences between sequentially acquired gradient echo images. However, for the use on abdominal organs, this renders the method very sensitive to motion artifacts and magnetic field changes. These motion artifacts can be coarsely classed into the two following types: intrascan motion artifacts and interscan motion artifacts. Intrascan motion artifacts are caused by displacement during the MR acquisition process and lead to image blurring and object ghosting. Commonly, this type of artifact is addressed using fast MR acquisition schemes or alternatively with respiratory-gated sequences that reduce the temporal resolution to the respiratory frequency. Interscan motion artifacts are due to organ displacement between the MR acquisitions and lead to a misregistration between subsequent phase images and thus to artifacts in the subtraction process. Furthermore, since any displacement or plastic deformation of the abdominal organs will in general also lead to a modified demagnetization field and thus to a change of the local magnetic field (6-8), additional phase artifacts are introduced.To overcome these problems, several correction strategies have been proposed, such as respiratory gating (9), navigator echoes (10), multibaseline acquisition to sample periodic changes (11,12), and referenceless phase corrections (13). Furthermore, the concept of the equivalent...