Simultaneous Quantitative MRI Mapping of T1, T2* and Magnetic Susceptibility with Multi-Echo MP2RAGE

Abstract

The knowledge of relaxation times is essential for understanding the biophysical mechanisms underlying contrast in magnetic resonance imaging. Quantitative experiments, while offering major advantages in terms of reproducibility, may benefit from simultaneous acquisitions. In this work, we demonstrate the possibility of simultaneously recording relaxation-time and susceptibility maps with a prototype Multi-Echo (ME) Magnetization-Prepared 2 RApid Gradient Echoes (MP2RAGE) sequence. T1 maps can be obtained using the MP2RAGE sequence, which is relatively insensitive to inhomogeneities of the radio-frequency transmit field, . As an extension, multiple gradient echoes can be acquired in each of the MP2RAGE readout blocks, which permits the calculation of and susceptibility maps. We used computer simulations to explore the effects of the parameters on the precision and accuracy of the mapping. In vivo parameter maps up to 0.6 mm nominal resolution were acquired at 7 T in 19 healthy volunteers. Voxel-by-voxel correlations and the test-retest reproducibility were used to assess the reliability of the results. When using optimized paramenters, T1 maps obtained with ME-MP2RAGE and standard MP2RAGE showed excellent agreement for the whole range of values found in brain tissues. Simultaneously obtained and susceptibility maps were of comparable quality as Fast Low-Angle SHot (FLASH) results. The acquisition times were more favorable for the ME-MP2RAGE (≈ 19 min) sequence as opposed to the sum of MP2RAGE (≈ 12 min) and FLASH (≈ 10 min) acquisitions. Without relevant sacrifice in accuracy, precision or flexibility, the multi-echo version may yield advantages in terms of reduced acquisition time and intrinsic co-registration, provided that an appropriate optimization of the acquisition parameters is performed.

Denoising High-field Multi-dimensional MRI with Local Complex PCA

“…Multi-parametric quantitative methods acquire multiple images within a single sequence, in order to estimate the underlying quantity (Helms et al 2008;Metere et al 2017;Caan et al, 2019). This is comparable to diffusion-weighted MR imaging (DWI) where multiple images with different weighting are acquired.…”

SNR efficiency of combined bipolar gradient echoes: Comparison of three-dimensional FLASH, MPRAGE, and multiparameter mapping with VFA-FLASH and MP2RAGE

“…In fact, the map is unusable, therefore the map from the VFA‐FLASH9 protocol was used instead to correct the proton density for decay. Good‐quality mapping from unipolar multiecho MP2RAGE was reported recently , but the total scan time was more than twice as long (∼18 min), and the field strength was 7T, which alone provides a significant SNR advantage compared with the present study. The VFA‐FLASH12 protocol yields the highest NR, but lower‐quality PD and T 1 maps.…”

“…A T 1 map can be calculated via a look‐up table, and if multiple echoes are acquired, and PD mapping are also possible. An MPM pipeline with MP2RAGE was also recently proposed to map T 1 , and quantitative susceptibility mapping using unipolar echoes .…”

Increased Sensitivity and Signal-to-Noise Ratio in Diffusion-Weighted MRI using Multi-Echo Acquisitions

“…Noise informed MLE fitting can be beneficial for the quantitative mapping of magnetic tissue properties. For example, noise informed MLE reconstruction could be advantageous for other quantitative MRI strategies using Multi-Echo acquisitions such as ME-FLASH (43) or ME-MP2RAGE (44). Multi-Echo reconstructions are commonly performed using LLS (45,46).…”