T₂ mapping with magnetization‐prepared 3D TSE based on a modified BIR‐4 T₂ preparation

Abstract

The purpose of this work was to investigate the performance of the modified BIR-4 T preparation for T mapping and propose a method to remove T quantification errors in the presence of large B and B offsets. The theoretical investigation of the magnetization evolution during the T preparation in the presence of B and B offsets showed deviations from a mono-exponential T decay (two parameter fit). A three parameter fit was used to improve T accuracy. Furthermore, a two parameter fit with an additional saturation preparation scan was proposed to improve T accuracy and precision. These three fitting methods were compared based on simulations, phantom measurements and an in vivo healthy volunteer study of the neck musculature using a 3D TSE readout. The results based upon the pure two parameter fit overestimated T in regions with high B offsets (up to 40% in phantoms). The three parameter fit T values were robust to B offsets but with higher standard deviation (up to 40% in simulations). The two parameter fit with the saturation preparation yielded high robustness towards B offsets with a noise performance comparable to that of the two parameter fit. In the volunteer study the T values obtained by the pure two parameter fit showed a dependence on the field inhomogeneities, whereas the T values from the proposed fitting approach were shown to be insensitive to B offsets. The proposed method enabled accurate and precise T mapping in the presence of large B and B offsets.

Patients with episodic migraine show increased T2 values of the trapezius muscles – an investigation by quantitative high-resolution magnetic resonance imaging

“…A T2 preparation duration of 15 – 30 – 45 ms was applied and an additional saturation preparation scan was acquired to mitigate quantification errors due to B0 inhomogeneities. The flip angle train was determined according to the vendor’s routines, leading to a constant signal over the entire shot for the relaxation properties of skeletal musculature ( 13 , 24 ). The FOV of the sequence covered the entire course of the trapezius muscle in the vertical axis and the entire body width at the shoulder level in the horizontal axis.…”

“…The T2-weighted raw images of the T2‐prepared 3D TSE sequence were processed by in-house developed scripts coded in MATLAB. A voxel-by-voxel fitting for the T2 value with additional accounting for B0 field inhomogeneities was applied as described previously ( 13 , 24 , 25 ). The obtained datasets were transferred to the open-source software Medical Imaging Interaction Toolkit (MITK; developed by the Division of Medical and Biological Informatics, German Cancer Research Center, Heidelberg, Germany; www.mitk.org ), followed by visual quality assessment.…”

Isotropic resolution diffusion tensor imaging of lumbosacral and sciatic nerves using a phase‐corrected diffusion‐prepared 3D turbo spin echo

“…) consists of an adiabatic diffusion preparation followed by a phase‐navigated 3D TSE readout. The adiabatic diffusion preparation has for an RF component a modified four‐segment B 1 ‐insensitive rotation (BIR‐4) pulse, previously shown to increase robustness against B 0 and transmit B 1 effects when applied for T 2 preparation . The modified RF configuration consists of a BIR‐4 pulse with gaps between the three RF components added to fit diffusion‐sensitizing gradients, where the total duration of the BIR‐4 RF pulse without gaps is 10 ms.…”

T2 mapping of the distal sciatic nerve in healthy subjects and patients suffering from lumbar disc herniation with nerve compression

“…Both thighs were scanned subsequently, with the side scanned first being subject to randomization. The scanning protocol included the following sequences: , SENSE acceleration factor = 2.5, T2 preparation applying a B1-insensitive rotation radiofrequency pulse as previously used [36,37], T2 preparation duration = 20/40/60/80 ms. Together with the effective T2 weighting during the TSE readout, the effective TE of the sequence was 47.9 ms, 67.9 ms, 87.9 ms, and 107.9 ms. was based on the T2-weighted DIXON images and the VOI was placed in such a way that it incorporated the distal sciatic nerve.…”