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Purpose: Three‐dimensional fast spin‐echo (FSE) sequences commonly use very long echo trains (>64 echoes) and severely reduced refocusing angles. They are increasingly used in brain exams due to high, isotropic resolution and reasonable scan time when using long trains and short interecho spacing. In this study, T2 quantification in 3D FSE is investigated to achieve increased resolution when comparing with established 2D (proton‐density dual‐echo and multi‐echo spin‐echo) methods. Methods: The FSE sequence design was explored to use long echo trains while minimizing T2 fitting error and maintaining typical proton density and T2‐weighted contrasts. Constant and variable flip angle trains were investigated using extended phase graph and Bloch equation simulations. Optimized parameters were analyzed in phantom experiments and validated in vivo in comparison to 2D methods for eight regions of interest in brain, including deep gray‐matter structures and white‐matter tracts. Results: Phantom and healthy in vivo brain T2 measurements showed that optimized variable echo‐train 3D FSE performs similarly to previous 2D methods, while achieving three‐fold‐higher slice resolution, evident visually in the 3D T2 maps. Optimization resulted in better T2 fitting and compared well with standard multi‐echo spin echo (within the 8‐ms confidence limits defined based on Bland‐Altman analysis). Conclusion: T2 mapping using 3D FSE with long echo trains and variable refocusing angles provides T2 accuracy in agreement with 2D methods with additional high‐resolution benefits, allowing isotropic views while avoiding incidental magnetization transfer effects. Consequently, optimized 3D sequences should be considered when choosing T2 mapping methods for high anatomic detail. [ABSTRACT FROM AUTHOR]

Purpose: To extract longitudinal and transverse (T1 and T2) relaxation maps from standard MRI methods. Methods: Bloch simulations were used to model relative signal amplitudes from standard turbo spin‐echo sequences: proton density weighted, T2‐weighted, and either T2‐weighted fluid attenuated inversion recovery or T1‐weighted images. Simulations over a range of expected parameter values yielded a look‐up table of relative signal intensities of these sequences. Weighted images and flip angle maps were acquired in 8 subjects at 3 T using both single and multislice acquisitions. The T1 and T2 maps were fit by comparing the weighted images to the look‐up table, given the measured flip angles. Results were compared with inversion recovery and multi‐echo spin‐echo experiments. Results: A region analysis showed that relaxation maps computed from single‐slice proton density, T2 and T1 weighting provided a mean T1 error of 4% in gray matter and 11% in white matter, and a mean T2 error of 3% and 4%, respectively, in comparison to reference measurements. In multislice acquisitions that are optimized to reduce cross‐talk and incidental magnetization transfer, the mean T1 error was 7% in gray matter and 1% in white matter, and the mean T2 errors were 3% and 4%, respectively. The best T1 results were achieved using proton density, T2 and T1 weighting rather than the fluid attenuated inversion recovery, although T2 maps were largely unaffected by this choice. Incidental magnetization transfer reduced T1 accuracy in standard interleaved multislice acquisitions. Conclusion: Through exact sequence modeling and separate flip angle measurement, T2 and T1 may be quantified from a turbo spin‐echo brain protocol with proton density, T2, and T1 weighting. [ABSTRACT FROM AUTHOR]

Background: Exponential fitting of multiecho spin echo sequences with skipped echoes is still commonly used for quantification of transverse relaxation (T2 ).Purpose: To examine the efficacy of skipped echo methods for T2 quantification against computational modeling of the exact signal decay.Study Type: Prospective comparison of methods.Subjects/phantom: Eight volunteers were imaged at 4.7T, six volunteers at 1.5T, and phantoms ([MnCl2 ] = 68-270 mM).Field Strength/sequence: 1.5T and 4.7T; multiple-echo spin echo.Assessment: Exponential fitting for T2 using all echoes, skipping the first echo or skipping all odd echoes, compared with Bloch simulations. Resulting T2 values were examined over a range of T2 (10-150 msec), refocusing flip angles (90-270°), and echo train lengths (ETL = 6-32).Statistical Tests: Shapiro-Wilk tests and Q-Q plots were used to check for normality of data. Paired sample t-tests and Wilcoxon rank tests were used to compare fitting models using α = 0.05. Multiple comparisons were accounted for with Bonferroni correction.Results: In examined regions of interest, typical incorrect estimation of T2 ranged from 23-39% for exponential fitting of all echoes, or 15-32% for skipped echo methods. In vivo, T2 estimation error was reduced to as little as 10% with skipped echo methods using 180° refocusing and ETL = 8, although error varied due to refocusing angle, T2 , and ETL. In vivo, skipped echo T2 values were significantly different than all echo exponential fitting (P < 0.004), but also were significantly different from reference values (P < 0.002, except frontal white matter). Simulations showed skipping the first echo was the most effective form of exponential fitting, in particular for T2 <50 msec and ETL = 8, with potential to reduce T2 errors to 10%, depending on refocusing angle and T2 .Data Conclusion: Skipping echoes is insufficient for avoiding stimulated echo contamination. Resulting T2 errors depend on a complicated interplay of T2 , refocusing angle, and ETL. Modeling of the multiecho sequence is recommended.Level Of Evidence: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:1432-1440. [ABSTRACT FROM AUTHOR]

Purpose To evaluate transverse relaxation (T2) and flip angle maps derived from signal pathway modeling of multiple spin echoes using simultaneous or independent T2 and flip angle fitting. Methods We examined different approaches to indirect and stimulated echo compensated T2 relaxometry from multiple spin echoes to evaluate both T2 and flip angle accuracy in simulation, phantom, and human brain. Signal pathways were modeled with or without independent flip angle maps using either Bloch simulations, or Extended Phase Graph (EPG) with Fourier or Shinnar-Le Roux approximation of slice profiles. Results Slice-selective decay curves differ substantially between models. Inaccurate flip angles are obtained with EPG methods, although T2 values are relatively accurate. Providing measured flip angles to EPG methods yields erroneous T2. Bloch methods improve both T2 and flip angle results. Simultaneous fitting can suffer from flip angle redundancy yielding multiple T2 solutions, particularly in low signal-to-noise ratio cases. Conclusion EPG fitting provides reasonably accurate T2, but is limited by poor accuracy in resulting flip angles, and T2 errors increase when flip angles are provided. Bloch simultaneous fitting of T2 and flip angle provides excellent results, but can be limited by multiple solutions which can be overcome by including a flip angle map. Magn Reson Med 77:2057-2065, 2017. © 2016 International Society for MagneticResonance in Medicine [ABSTRACT FROM AUTHOR]

Macromolecular gadolinium (Gd)-based contrast agents are in development as blood pool markers for MRI. HPG-GdF is a 583 kDa hyperbranched polyglycerol doubly tagged with Gd and Alexa 647 nm dye, making it both MR and histologically visible. In this study we examined the location of HPG-GdF in whole-tumor xenograft sections matched to in vivo DCE-MR images of both HPG-GdF and Gadovist. Despite its large size, we have shown that HPG-GdF extravasates from some tumor vessels and accumulates over time, but does not distribute beyond a few cell diameters from vessels. Fractional plasma volume (fPV) and apparent permeability-surface area product (aPS) parameters were derived from the MR concentration-time curves of HPG-GdF. Non-viable necrotic tumor tissue was excluded from the analysis by applying a novel bolus arrival time (BAT) algorithm to all voxels. aPS derived from HPG-GdF was the only MR parameter to identify a difference in vascular function between HCT116 and HT29 colorectal tumors. This study is the first to relate low and high molecular weight contrast agents with matched whole-tumor histological sections. These detailed comparisons identified tumor regions that appear distinct from each other using the HPG-GdF biomarkers related to perfusion and vessel leakiness, while Gadovist-imaged parameter measures in the same regions were unable to detect variation in vascular function. We have established HPG-GdF as a biocompatible multi-modal high molecular weight contrast agent with application for examining vascular function in both MR and histological modalities. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Purpose: Three-dimensional fast spin-echo (FSE) sequences commonly use very long echo trains (>64 echoes) and severely reduced refocusing angles. They are increasingly used in brain exams due to high, isotropic resolution and reasonable scan time when using long trains and short interecho spacing. In this study, T 2 quantification in 3D FSE is investigated to achieve increased resolution when comparing with established 2D (proton-density dual-echo and multi-echo spin-echo) methods., Methods: The FSE sequence design was explored to use long echo trains while minimizing T 2 fitting error and maintaining typical proton density and T 2 -weighted contrasts. Constant and variable flip angle trains were investigated using extended phase graph and Bloch equation simulations. Optimized parameters were analyzed in phantom experiments and validated in vivo in comparison to 2D methods for eight regions of interest in brain, including deep gray-matter structures and white-matter tracts., Results: Phantom and healthy in vivo brain T 2 measurements showed that optimized variable echo-train 3D FSE performs similarly to previous 2D methods, while achieving three-fold-higher slice resolution, evident visually in the 3D T 2 maps. Optimization resulted in better T 2 fitting and compared well with standard multi-echo spin echo (within the 8-ms confidence limits defined based on Bland-Altman analysis)., Conclusion: T 2 mapping using 3D FSE with long echo trains and variable refocusing angles provides T 2 accuracy in agreement with 2D methods with additional high-resolution benefits, allowing isotropic views while avoiding incidental magnetization transfer effects. Consequently, optimized 3D sequences should be considered when choosing T 2 mapping methods for high anatomic detail., (© 2021 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)

Purpose: To extract longitudinal and transverse (T 1 and T 2 ) relaxation maps from standard MRI methods., Methods: Bloch simulations were used to model relative signal amplitudes from standard turbo spin-echo sequences: proton density weighted, T 2 -weighted, and either T 2 -weighted fluid attenuated inversion recovery or T 1 -weighted images. Simulations over a range of expected parameter values yielded a look-up table of relative signal intensities of these sequences. Weighted images and flip angle maps were acquired in 8 subjects at 3 T using both single and multislice acquisitions. The T 1 and T 2 maps were fit by comparing the weighted images to the look-up table, given the measured flip angles. Results were compared with inversion recovery and multi-echo spin-echo experiments., Results: A region analysis showed that relaxation maps computed from single-slice proton density, T 2 and T 1 weighting provided a mean T 1 error of 4% in gray matter and 11% in white matter, and a mean T 2 error of 3% and 4%, respectively, in comparison to reference measurements. In multislice acquisitions that are optimized to reduce cross-talk and incidental magnetization transfer, the mean T 1 error was 7% in gray matter and 1% in white matter, and the mean T 2 errors were 3% and 4%, respectively. The best T 1 results were achieved using proton density, T 2 and T 1 weighting rather than the fluid attenuated inversion recovery, although T 2 maps were largely unaffected by this choice. Incidental magnetization transfer reduced T 1 accuracy in standard interleaved multislice acquisitions., Conclusion: Through exact sequence modeling and separate flip angle measurement, T 2 and T 1 may be quantified from a turbo spin-echo brain protocol with proton density, T 2 , and T 1 weighting., (© 2018 International Society for Magnetic Resonance in Medicine.)