Rapid acquisition of multifrequency, multislice and multidirectional MR elastography data with a fractionally encoded gradient echo sequence

Abstract

In MR elastography (MRE), periodic tissue motion is phase encoded using motion-encoding gradients synchronized to an externally applied periodic mechanical excitation. Conventional methods result in extended scan time for quality phase images, thus limiting the broad application of MRE in the clinic. For practical scan times, researchers have been relying on one-dimensional or two-dimensional motion-encoding, low-phase sampling and a limited number of slices, and artifact-prone, single-shot, echo planar imaging (EPI) readout. Here, we introduce a rapid multislice pulse sequence capable of three-dimensional motion encoding that is also suitable for simultaneously encoding motion with multiple frequency components. This sequence is based on a gradient-recalled echo (GRE) sequence and exploits the principles of fractional encoding. This GRE MRE pulse sequence was validated as capable of acquiring full three-dimensional motion encoding of isotropic voxels in a large volume within less than a minute. This sequence is suitable for monofrequency and multifrequency MRE experiments. In homogeneous paraffin phantoms, the eXpresso sequence yielded similar storage modulus values as those obtained with conventional methods, although with markedly reduced variances (7.11 ± 0.26 kPa for GRE MRE versus 7.16 ± 1.33 kPa for the conventional spin-echo EPI sequence). The GRE MRE sequence obtained better phase-to-noise ratios than the equivalent spin-echo EPI sequence (matched for identical acquisition time) in both paraffin phantoms and in vivo data in the liver (59.62 ± 11.89 versus 27.86 ± 3.81, 61.49 ± 14.16 versus 24.78 ± 2.48 and 58.23 ± 10.39 versus 23.48 ± 2.91 in the X, Y and Z components, respectively, in the case of liver experiments). Phase-to-noise ratios were similar between GRE MRE used in monofrequency or multifrequency experiments (75.39 ± 14.93 versus 86.13 ± 18.25 at 28 Hz, 71.52 ± 24.74 versus 86.96 ± 30.53 at 56 Hz and 95.60 ± 36.96 versus 61.35 ± 26.25 at 84Hz, respectively).

New imaging techniques for liver diseases

“…These visco-elastic properties include the shear modulus G ⁄ , the storage modulus Gd reflecting elasticity, and the loss modulus Gl reflecting viscosity. Moreover, with multifrequency MR elastography, the wave scattering coefficient corresponding to the slope of the visco-elasticity vs. frequency curve can be obtained [24,114].…”

MR Elastography Can Be Used to Measure Brain Stiffness Changes as a Result of Altered Cranial Venous Drainage During Jugular Compression

“…Tissue displacements were imaged in 3 directions at 8 time points during the sinusoidal vibration with a fastfield echo MRE sequence. 21 Imaging parameters were the following: FOV ϭ 192 ϫ 192 mm, matrix ϭ 96 ϫ 96, 9 sections, section thickness ϭ 2-mm, TR/TE ϭ 104.1/9.2 ms, flip angle ϭ 20°, sensitivity encoding ϭ 1.5 with no k-space reduction. Acquisition time was 4 minutes.…”

In vivo high-resolution magnetic resonance elastography of the uterine corpus and cervix

“…Preliminary quantitative values of uterine leiomyomas have been reported using MRE [9], although in those studies there was no analysis of healthy uterine tissue. Recent developments in driver technology, accelerated MRE sequences [10][11][12] and multifrequency reconstruction algorithms [13] make highresolution elastography of abdominal and intrapelvic tissue technically feasible.…”