Three‐dimensional simultaneous brain mapping of T1, T2, and magnetic susceptibility with MR Multitasking

Abstract

Purpose To develop a new technique that enables simultaneous quantification of whole‐brain T1, T2, T2∗, as well as susceptibility and synthesis of six contrast‐weighted images in a single 9.1‐minute scan. Methods The technique uses hybrid T2‐prepared inversion‐recovery pulse modules and multi‐echo gradient‐echo readouts to collect k‐space data with various T1, T2, and T2∗ weightings. The underlying image is represented as a six‐dimensional low‐rank tensor consisting of three spatial dimensions and three temporal dimensions corresponding to T1 recovery, T2 decay, and multi‐echo behaviors, respectively. Multiparametric maps were fitted from reconstructed image series. The proposed method was validated on phantoms and healthy volunteers, by comparing quantitative measurements against corresponding reference methods. The feasibility of generating six contrast‐weighted images was also examined. Results High quality, co‐registered T1, T2, and T2∗ susceptibility maps were generated that closely resembled the reference maps. Phantom measurements showed substantial consistency (R2 > 0.98) with the reference measurements. Despite the significant differences of T1 (p < .001), T2 (p = .002), and T2∗ (p = 0.008) between our method and the references for in vivo studies, excellent agreement was achieved with all intraclass correlation coefficients greater than 0.75. No significant difference was found for susceptibility (p = .900). The framework is also capable of synthesizing six contrast‐weighted images. Conclusion The MR Multitasking–based 3D brain mapping of T1, T2, T2∗, and susceptibility agrees well with the reference and is a promising technique for multicontrast and quantitative imaging.

MR multitasking‐based dynamic imaging for cerebrovascular evaluation (MT‐DICE): Simultaneous quantification of permeability and leakage‐insensitive perfusion by dynamic T1/T2* mapping

“…Eight subjects (aged 24-67 y, three females) without known brain abnormalities were recruited. MT 36 and our pilot study shown in Supporting Information Appendix S1, Section C), SR period (the temporal resolution of dynamic T 1 ∕T * 2 mapping) is approximately 1.2 s, containing 60 segments at time points varying from 19.30 to 1160 ms, flip angle = 10 • , total time = 7.6 min. Single dose (0.1 mmol/kg of body weight) of CA (Gadavist; Bayer Schering Pharma, Berlin, Germany) was administered through antecubital intravenous access 1.5 min into the scan at the rate of 3.0 mL/s, followed by a 20 mL saline flush at the same rate.…”

“…Eight subjects (aged 24–67 y, three females) without known brain abnormalities were recruited. MT‐DICE imaging was performed in an oblique transverse orientation with the following imaging parameters: field‐of‐view (FOV) = 216 × 216 × 128 mm 3 , spatial resolution = 1.5 × 1.5 × 4.0 mm 3 , pulse TR = 19.30 ms, TEs = 2.46/4.92/7.38/9.84/12.30/17.22 ms (which is enough to generate relatively accurate $$$ {\mathrm{T}}_2^{\ast } $$$ maps, according to 36 and our pilot study shown in Supporting Information Appendix S1, Section C), SR period (the temporal resolution of dynamic $$$ {\mathrm{T}}_1/{\mathrm{T}}_2^{\ast } $$$ mapping) is approximately 1.2 s, containing 60 segments at time points varying from 19.30 to 1160 ms, flip angle = 10°, total time = 7.6 min. Single dose (0.1 mmol/kg of body weight) of CA (Gadavist; Bayer Schering Pharma, Berlin, Germany) was administered through antecubital intravenous access 1.5 min into the scan at the rate of 3.0 mL/s, followed by a 20 mL saline flush at the same rate.…”

Free‐breathing, non‐ECG, simultaneous myocardial T1, T2, T2*, and fat‐fraction mapping with motion‐resolved cardiovascular MR multitasking

“…Constant TR Multitasking using multi-echo readouts and a constant TR for both training and imaging data has been recently presented for T 2 * mapping in the brain 30 and T 2 */FF mapping in the liver. 31 The VTR approach proposed in this work clearly outperformed the CTR approach in motion phantoms and in the heart, as shown in Figure 3 and Supporting Information Figures S4 and S5.…”

“…Two interleaved data sets are collected during the continuous acquisition: The training data ($$$ {\mathbf{d}}_{\mathrm{tr}} $$$) are frequently collected at k‐space center (0° radial spoke) to provide temporal information, and the imaging data ($$$ {\mathbf{d}}_{\mathrm{img}} $$$) are collected with golden‐angle radial trajectory to provide spatial information. In previous MR Multitasking work for T 2 * mapping, 30,31 multi‐echo readouts were used for both training and imaging data (Figure 1B), which limited the temporal resolution and imaging efficiency. To achieve a higher temporal resolution to characterize cardiac motion, instead of using constant T R (CTR) for both datasets, a VTR scheme was developed in this work, in which the training data are collected using a single‐echo, short T R readout and imaging data are collected using a multi‐echo, long T R readout (Figure 1C).…”

“…However, this framework has yet to include T 2 * and fat fraction (FF) mapping in the heart. Multi‐echo extensions of Multitasking for T 1 , T 2 , and T 2 * mapping in the brain 30 and T 1 , R 2 *, and FF mapping in the liver 31 have been described. However, adding multiple echoes after every excitation pulse comes at the price of prolonged scan time and reduced temporal resolution, limiting the direct translation of these multi‐echo extensions to cardiac imaging.…”