Balanced spin‐lock preparation for B₁‐insensitive and B₀‐insensitive quantification of the rotating frame relaxation time T_1ρ

Abstract

Purpose Accurate and artifact‐free T1ρ quantification is still a major challenge due to a susceptibility of the spin‐locking module to B0 and/or B1 field inhomogeneities. In this study, we present a novel spin‐lock preparation module (B‐SL) that enables an almost full compensation of both types of inhomogeneities. Methods The new B‐SL module contains a second 180° refocusing pulse to compensate each pulse in the preparation block by a corresponding pulse with opposite phase. For evaluation and validation of B‐SL, extensive simulations as well as phantom measurements were performed. Furthermore, the new module was compared to three common established compensation methods. Results Both simulations and measurements demonstrate a much lower susceptibility to artifacts for the B‐SL module, therefore providing an improved accuracy in T1ρ quantification. In the presence of field inhomogeneities, measurements revealed an increased banding compensation by 79% compared with the frequently used composite module. The goodness of the mono‐exponential T1ρ fitting procedure was improved by 58%. Conclusion The B‐SL preparation enables the generation of accurate relaxation maps with significantly reduced artifacts, even in the case of large field imperfections. Therefore, the B‐SL module is suggested to be highly beneficial for in vivo T1ρ quantification.

Simultaneous comprehensive liver T1, T2, , T1ρ, and fat fraction characterization with MR fingerprinting

“…Because the multiparametric quantification is performed on several tissues, including liver, the dictionary T 1 , T 2 , and T 1⍴ combinations were chosen to represent a broad range of combinations that 20 five SL pulses are applied here with different SLT in order to provide additional T 1⍴ encoding. The SL pulses used in this work are totally balanced, 29,44,45 which have been shown to be robust to B 1 and B 0 inhomogeneities. [46][47][48] A SL amplitude of SLA = 350 Hz was chosen for these experiments.…”

Establishing an in vitro model of MR-T1ρ imaging technology to quantify nucleus pulposus tissue proteoglycans: a preliminary study

“…The quantification and calibration of T1ρ values are technical difficulties in the clinical setting (19), and some methods have been reported to calibrate T1ρ values to increase the detection rate of diseases (20)(21)(22). In the present study, we set up in vitro model samples with different proteoglycan content or water content to simulate different degenerated nucleus pulposus tissues.…”

An efficient R1ρ dispersion imaging method for human knee cartilage using constant magnetization prepared turbo‐FLASH

“…A pair of refocusing RF pulses (180 ) was inserted in the middle of two pairs of antiphase rotary-echo pulses as sketched in Figure 1A, leading to fully refocusing the chemical shift (Δω 0 ) artifacts from non-uniform B 0 even when the FA of the refocusing pulse was not exactly equal to 180 because of B 1 inhomogeneity. 32,35 R 1ρ dispersion imaging was performed on an Ingenia 3 T MR system (Philips Healthcare, Best, The Netherlands) in the sagittal plane, using a 16-channel T/R knee coil that was capable of generating an SL amplitude as high as 1150 Hz, ie a maximum B 1 27 μT. Each R 1ρ -weighted image was acquired using a pair of T SL and ω 1 as listed in Table 1.…”

“…Without any concerns on the SAR issues, the employed turbo FLASH sequence in the proposed R 1ρ dispersion acquisition has been demonstrated to be nearly as efficient as EPI. 37 While the implemented SL scheme has been demonstrated to be less prone to the image artefacts associated with non-uniform B 0 and B 1 fields, 32,35 the deviations of actual B 1 fields from the prescribed ones might still have an adverse effect on the accuracy of R 1ρ dispersion quantification, particularly on the edged imaging slices in the human knee where the B 1 inhomogeneity (ie ΔB 1 ) usually deteriorates. In the literature, 47 ΔB 1 has been demonstrated to be relatively small (5%) in the human knee cartilage, and our previous B 1 mapping (data not shown) was largely consistent with the literature.…”

“…It has been well documented that the prepared SL magnetization (M prep ) is highly susceptible to B 0 and B 1 non-uniform field artifacts. [28][29][30][31][32] Although many advanced SL schemes, including those using adiabatic pulses, have been developed in the past, none of these methods was specifically designed or optimized for R 1ρ dispersion imaging using a broad range of ω 1 .…”