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

Abstract

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.

Monocyte and/or Macrophage Infiltration of Heart after Myocardial Infarction: MR Imaging by Using T1-shortening Liposomes

“…and F.H.E., with 3 and 20 years of experience, respectively) by using custom-written programs developed in MATLAB (Mathworks, Natick, Mass). For cine DENSE images, circumferential strain (E cc ) was calculated (25). A marked deficit in circumferential strain (E cc greater than −0.06) was used to define the infarct zone (26,27).…”

Tracking brain motion during the cardiac cycle using spiral cine-DENSE MRI

“…22 Briefly speaking, complementary raw data sets for each displacement-encoding direction were subtracted as the CSPAMM reconstruction to suppress the T1-relaxation echo. A 2D inverse Fourier transform ͑2D-IFT͒ was applied to create complex images.…”

“…The phase images with displacement encoded in each orthogonal direction were then reconstructed and corrected for background phase error using the phase reference images. A quality-guided path following spatiotemporal ͑two spatial dimensions and time͒ phaseunwrapping algorithm 22 was applied to the pixels within the boundary of the brain tissue, in which a seed point was selected at the center of the brain tissue on the first cardiac phase assuming no phase wrap occurred at the initial time, and a measure of phase "quality" was then used to guide the path of unwrapping from pixel to pixel. Dividing the unwrapped phase value of each pixel by the displacement encoding frequency then directly yielded the displacement of this pixel relative to the time when the displacement encoding was initiated.…”

The role of imaging and molecular imaging in the early detection of metabolic and cardiovascular dysfunctions

“…With regard to the regional function, two MR techniques can provide strain curves: DENSE 16,17 and TAGGING. 18,19 Myocardial tagging allows assessment of the regional function of the LV.…”