Displacement encoding with stimulated echoes (DENSE) encodes myocardial tissue displacement into the phase of the MR image. Cine DENSE allows for rapid quantification of myocardial displacement at multiple cardiac phases through the majority of the cardiac cycle. For practical sensitivities to motion, relatively high displacement encoding frequencies are used and phase wrapping typically occurs. In order to obtain absolute measures of displacement, a two-dimensional (2-D) quality-guided phase unwrapping algorithm was adapted to unwrap both spatially and temporally. Both a fully automated algorithm and a faster semi-automated algorithm are proposed. A method for computing the 2-D trajectories of discrete points in the myocardium as they move through the cardiac cycle is introduced. The error in individual displacement measurements is reduced by fitting a time series to sequential displacement measurements along each trajectory. This improvement is in turn reflected in strain maps, which are derived directly from the trajectories. These methods were validated both in vivo and on a rotating phantom. Further measurements were made to optimize the displacement encoding frequency and to estimate the baseline strain noise both on the phantom and in vivo. The fully automated phase unwrapping algorithm was successful for 767 out of 800 images (95.9%), and the semi-automated algorithm was successful for 786 out of 800 images (98.3%). The accuracy of the tracking algorithm for typical cardiac displacements on a rotating phantom is 0.24 +/- 0.15 mm. The optimal displacement encoding frequency is in the region of 0.1 cycles/mm, and, for 2 scans of 17-s duration, the strain noise after temporal fitting was estimated to be 2.5 +/- 3.0% at end-diastole, 3.1 +/- 3.1% at end-systole, and 5.3 +/- 5.0% in mid-diastole. The improvement in intra-myocardial strain measurements due to temporal fitting is apparent in strain histograms, and also in identifying regions of dysfunctional myocardium in studies of patients with infarcts.

A navigator-gated 3D spiral cine displacement encoding with stimulated echoes (DENSE) pulse sequence for imaging 3D myocardial mechanics was developed. In addition, previously described 2D postprocessing algorithms including phase unwrapping, tissue tracking, and strain tensor calculation for the left ventricle (LV) were extended to 3D. These 3D methods were evaluated in five healthy volunteers, using 2D cine DENSE and historical 3D myocardial tagging as reference standards. With an average scan time of 20.5 6 5.7 min, 3D data sets with a matrix size of 128 3 128 3 22, voxel size of 2.8 3 2.8 3 5.0 mm 3 , and temporal resolution of 32 msec were obtained with displacement encoding in three orthogonal directions. Mean values for end-systolic mid-ventricular mid-wall radial, circumferential, and longitudinal strain were 0.33 6 0.10, 20.17 6 0.02, and 20.16 6 0.02, respectively. Transmural strain gradients were detected in the radial and circumferential directions, reflecting high spatial resolution. Good agreement by linear correlation and Bland-Altman analysis was achieved when comparing normal strains measured by 2D and 3D cine DENSE. Also, the 3D strains, twist, and torsion results obtained by 3D cine DENSE were in good agreement with historical values measured by 3D myocardial tagging. Magn Reson Med 64:1089-1097, 2010. V C 2010 WileyLiss, Inc.Key words: three dimensional; DENSE; myocardial mechanics; cardiac function; stimulated echo; strain Quantitative imaging of myocardial motion and strain is of growing importance. In addition to conventional applications such as ischemia detection (1,2) and evaluation of myocardial mechanics related to cardiac surgery (3-5), newer applications include quantifying mechanical dyssynchrony in heart failure (6,7), and measuring the functional effects of experimental therapies such as stem cells (8). Potential advantages of quantitative methods are that they may improve diagnostic sensitivity and specificity (9), may reduce subjectivity and intraobserver and interobserver variability, and may facilitate statistical comparisons of cardiac function between different experimental groups.While quantitative two-dimensional (2D) imaging is more common than three-dimensional (3D) imaging, motion of the left ventricle (LV) is, in fact, complex and 3D. The myocardial strain tensor has significant components in the radial, circumferential and longitudinal directions, as well as important off-diagonal components, reflecting the 3D contraction, twist, and torsion that are integral to efficient pump function. A technique that is 3D both with respect to spatial coverage and motion measurement is required for a complete assessment of LV motion. Three-dimensional myocardial tagging MRI has previously been used to noninvasively measure the 3D mechanics of the LV in detail (10-13), and these data provide a reference standard against which new methods may be compared. However, strain analysis of 3D tagged MR images is laborious and time consuming due to the need to detect tag lines, rendering th...

This multi-step adaptive fitting approach performed well in both simulated and initial clinical evaluation, and shows potential in the quantification of hepatic steatosis.

1 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:431-439.