A breath-hold two-dimensional cine magnetic resonance (MR) pulse sequence based on displacement encoding with stimulated echoes (DENSE) for quantitative myocardial motion tracking was developed and evaluated. In the sequence, complementary spatial modulation of magnetization was used for time-independent artifact suppression, and echo-planar imaging was used for rapid data sampling. Twelve healthy volunteers underwent cine DENSE MR imaging, and six of them also underwent conventional MR imaging myocardial tagging. The circumferential shortening component of strain (E(cc)) was measured on cine DENSE MR images and conventional tagged MR images. With complementary spatial modulation of magnetization, 10% or less of the total cine DENSE MR image energy was attributed to an artifact-generating echo during systolic imaging. Two-dimensional intramyocardial displacement and strain were measured at cine DENSE MR imaging with spatial resolution and temporal resolution of 2.7 x 2.7 mm and 60 msec, respectively. E(cc) measured at cine DENSE MR imaging correlated well with that measured at conventional MR imaging tagging (slope = 0.88, intercept = 0.00, R = 0.87).

Myocardial Tissue Tracking with Two-dimensional Cine Displacement-encoded MR Imaging: Development and Initial Evaluation

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 0.24plusmn0.15mm. 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 2.5plusmn3.0% at end-diastole, 3.1plusmn3.1% at end-systole, and 5.3plusmn5.0% 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

Tracking Myocardial Motion From Cine DENSE Images Using Spatiotemporal Phase Unwrapping and Temporal Fitting

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From the Publisher:
In recent years, the use of finite element analysis as a design tool has grown rapidly. Easy to use comprehensive packages such as ANSYS, a general-purpose finite element computer program, have become common tools in the hands of engineers. This book is written to assist engineering students and practicing engineers new to the field of finite element modeling, to gain a clear understanding of the fundamentals of finite element modeling. The text offers insight into the theoretical aspects of finite element analysis and great care has been exercised to avoid overwhelming students with theory. Yet, enough theoretical background is offered to allow individuals to use ANSYS intelligently and effectively. ANSYS is an integral part of this text.

Saeed Moaveni

Papers

Finite Element Analysis: Theory and Application With Ansys