Water proton T 1 measurements in brain tissue at 7, 3, and 1.5T using IR-EPI, IR-TSE, and MPRAGE: results and optimization

Wright, Philip; Mougin, Olivier; Totman, John J.; Peters, Andrew M.; Brookes, Matthew J.; Coxon, R.; Morris, Peter D.; Clemence, M; Francis, Susan T.; Bowtell, Richard; Gowland, Penny A.

doi:10.1007/s10334-008-0104-8

Cited by 238 publications

(248 citation statements)

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“…This can be due to the choice of sequence or its parameters, the fitting routines or not taking into account the efficiency of the inversion and hence, each different study has a well-defined bias or simply very different populations between studies (both age and gender are known to affect longitudinal relaxation times). The T 1 estimates presented here are in a good agreement with previous reports at 3 T (Lu et al, 2005;Wansapura et al, 1999;Wright et al, 2008). T 1 values at 7 T were in agreement, within the experimental error, with previous studies, although both cortical and subcortical grey matter approximately 10% shorter than the study by (Rooney et al, 2007).…”

Section: Discussionsupporting

confidence: 92%

MP2RAGE, a self bias-field corrected sequence for improved segmentation and T1-mapping at high field

et al. 2010

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The large spatial inhomogeneity in transmit B 1 field (B 1 + ) observable in human MR images at high static magnetic fields (B 0 ) severely impairs image quality. To overcome this effect in brain T 1 -weighted images, the MPRAGE sequence was modified to generate two different images at different inversion times, MP2RAGE. By combining the two images in a novel fashion, it was possible to create T 1 -weigthed images where the result image was free of proton density contrast, T 2 ⁎ contrast, reception bias field, and, to first order, transmit field inhomogeneity. MP2RAGE sequence parameters were optimized using Bloch equations to maximize contrast-to-noise ratio per unit of time between brain tissues and minimize the effect of B 1 + variations through space. Images of high anatomical quality and excellent brain tissue differentiation suitable for applications such as segmentation and voxel-based morphometry were obtained at 3 and 7 T. From such T 1 -weighted images, acquired within 12 min, high-resolution 3D T 1 maps were routinely calculated at 7 T with sub-millimeter voxel resolution (0.65-0.85 mm isotropic). T 1 maps were validated in phantom experiments. In humans, the T 1 values obtained at 7 T were 1.15 ± 0.06 s for white matter (WM) and 1.92 ± 0.16 s for grey matter (GM), in good agreement with literature values obtained at lower spatial resolution. At 3 T, where whole-brain acquisitions with 1 mm isotropic voxels were acquired in 8 min, the T 1 values obtained (0.81 ± 0.03 s for WM and 1.35 ± 0.05 for GM) were once again found to be in very good agreement with values in the literature. © 2009 Elsevier Inc. All rights reserved. IntroductionIn the past decade, the magnetization-prepared rapid gradient echo, MPRAGE (Mugler and Brookeman, 1990), sequence has become one of the most commonly used sequences to obtain T 1 -weighted anatomical images of the human brain, in particular at high magnetic field. MPRAGE images are routinely used as anatomical reference for fMRI or for brain tissue classification in voxel-based morphometry (Ashburner and Friston, 2000). However, at high static magnetic fields (≥ 3 T), the increased inhomogeneity of the transmit B 1 + and receive B 1 − fields creates intensity variations throughout the image (bias field). Bias fields not only render segmentation and quantitative analysis difficult but also severely affect image quality at ultra-high fields (≥7 T). The use of adiabatic pulses to perform the inversion in the MPRAGE is only partially able to mitigate the effects of inhomogeneous B 1 . A number of strategies have been proposed to minimize or to correct bias fields generated by the inhomogeneity of the B 1 fields. Most correction strategies aim at correcting the combined (transmit and receive) bias field via post-processing techniques. This can be done either by low-pass filtering (Cohen et al., 2000;Wald et al., 1995) or by fitting slowly varying functions such as Gaussians or low order polynomials (Styner et al., 2000). The result from these low pass filters or fits is then su...

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Section: Discussionsupporting

confidence: 92%

MP2RAGE, a self bias-field corrected sequence for improved segmentation and T1-mapping at high field

et al. 2010

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“…However, image contrast and signal intensity changes occurring during the first year of life necessitate careful optimization of the experimental parameters used in neonatal MRI [13][14][15][16][17][18]. In neonates, image contrast is inverted relative to adults [19][20][21][22], as relaxation times of white matter (WM) are longer than those of gray matter (GM) [15,23]. Decreases in brain water content, neuronal and synaptic development and increases in the concentration of macromolecules associated with myelin cause T1 and T2 relaxation times to decrease significantly during the first 2 years [1,2,5,8,18].…”

Section: Introductionmentioning

confidence: 99%

Optimized T1- and T2-weighted volumetric brain imaging as a diagnostic tool in very preterm neonates

et al. 2010

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Background T1-and T 2 -W MR sequences used for obtaining diagnostic information and morphometric measurements in the neonatal brain are frequently acquired using different imaging protocols. Optimizing one protocol for obtaining both kinds of information is valuable. Objective To determine whether high-resolution T1-and T 2 -W volumetric sequences optimized for preterm brain imaging could provide both diagnostic and morphometric value. Materials and methods Thirty preterm neonates born between 24 and 32 weeks' gestational age were scanned during the first 2 weeks after birth. T1-and T 2 -W highresolution sequences were optimized in terms of signal-tonoise ratio, contrast-to-noise ratio and scan time and compared to conventional spin-echo-based sequences. Results No differences were found between conventional and high-resolution T 1 -W sequences for diagnostic confidence, image quality and motion artifacts. A preference for conventional over high-resolution T 2 -W sequences for image quality was observed. High-resolution T1 images provided better delineation of thalamic myelination and the superior temporal sulcus. No differences were found for detection of myelination and sulcation using conventional and high-resolution T 2 -W images. Conclusion High-resolution T1-and T 2 -W volumetric sequences can be used in clinical MRI in the very preterm brain to provide both diagnostic and morphometric information.R. Nossin-Manor (*)

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“…5,[17][18][19][20][21][22][23][24] The measured relaxation values at 3T were: GM, T 1 v (1524 ms) and T 2 v (85 ms) and WM, T 1 v (750 ms) and T 2 v (65 ms). At 1.5T, they were: GM, T 1 v (1251 ms) and T 2 v (99 ms) and WM, T 1 v (623 ms) and T 2 v (75 ms).…”

Section: Resultsmentioning

confidence: 98%

Optimization of Scan Parameters for T1-FLAIR Imaging at 1.5 and 3T using Computer Simulation

et al. 2013

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Purpose: We attempted to optimize scan parameters for T 1 -weighted ‰uid-attenuated inversion recovery (T 1 -FLAIR) sequence at 3 and 1.5 tesla (T) using computer simulation.Methods: We measured the T 1 and T 2 relaxation time values (T 1 v and T 2 v) of gray (GM) and white matter (WM) at 3 and 1.5T, generated computer-simulated T 1 -FLAIR (CS-T 1 -FLAIR) images using those values, and compared the simulated and actual T 1 -FLAIR images to verify the contrast reliability of our computer simulation. We mathematically and visually evaluated CS-T 1 -FLAIR images at various repetition times (TR) and echo times (TE).Results: At 3T, the measured relaxation values for GM were T 1 v, 1524 ms, and T 2 v, 85 ms, and for WM, T 1 v, 750 ms, and T 2 v, 65 ms. At 1.5T, the measured relaxation values for GM were T 1 v, 1251 ms, and T 2 v, 99 ms, and for WM, T 1 v, 623 ms, and T 2 v, 75 ms. Contrast of CS-T 1 -FLAIR and actual T 1 -FLAIR images was identical. An optimal TR of 3140 ms was determined for T 1 -FLAIR at 3T and 2440 ms at 1.5T based on mathematical evaluation. The optimal TR ranges were 2400 to 3900 ms at 3T and 1800 to 3200 ms at 1.5T based on visual assessment of CS-T 1 -FLAIR. A shorter TE provided better T 1 contrast.Conclusion: We optimized T 1 -FLAIR by focusing on its most important scan parameters using computer simulations and determined that a longer TR was suitable at 3T than at 1.5T. Our computer simulation was useful for determining the optimal scan parameters.

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Water proton T 1 measurements in brain tissue at 7, 3, and 1.5T using IR-EPI, IR-TSE, and MPRAGE: results and optimization

Cited by 238 publications

References 20 publications

MP2RAGE, a self bias-field corrected sequence for improved segmentation and T1-mapping at high field

MP2RAGE, a self bias-field corrected sequence for improved segmentation and T1-mapping at high field

Optimized T1- and T2-weighted volumetric brain imaging as a diagnostic tool in very preterm neonates

Optimization of Scan Parameters for T1-FLAIR Imaging at 1.5 and 3T using Computer Simulation

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