1. ABSTRACT
Background: Although 2D strain imaging has shown promise to define myocardial dysfunction, it provides only subjective assessment about the extent of dysfunction due to limited scanning window and is subject to errors due to through-plane myocardial motion. We studied a new 3D based strain method on open chest pigs.
Methods: We studied five adult pigs that underwent midline sternotomy to expose their heart for high resolution ultrasound scanning directly from the surface of the heart. The left anterior descending coronary artery (LAD) was isolated from the vein and arbitrarily divided into three equal zones from the LV apex distally to the origin of the first diagonal branch proximally. Baseline 3D full volume image loops were acquired from apex with an X7-2 probe on a Phillips IE 33 ultrasound system. The LAD was occluded in the distal-most zone first and the visibly ischemic area, as shown by change in color, was measured and 3D full volume images acquired. The study was repeated after occluding the LAD in proximal zones. Images were analyzed offline in an envelope detected MatLab based program. Average image size was 192 x 237 x 214 voxels with 0.63 mm/voxel spatial and 20 volume/cycle temporal resolution.
Results: Images were analyzed to obtain the color coded strain maps and dysfunctional area was measured from display in end-systolic frames. Average size of infarct was x mm for distal LAD occlusion and x mm for proximal LAD occlusion. Extending the level of LAD ligation proximally also increased the size of ischemic zone as measured from color change on the surface of heart that correlated with the size of myocardial dysfunction as quantified from parametric strain maps from 3D image analysis.
Conclusions: Three-dimensional strain maps could provide an objective evaluation of myocardial dysfunction in coronary ischemia.
DISCLOSURES
No relationships to disclose:
Muhammad Ashraf Andriy Myronenko
Xubo Song Zhiwen Zhou
Keith DesRochers Uyen T. Truong
David J. Sahn
BACKGROUND
Echocardiography derived strain and strain rate have emerged as quantitative techniques to estimate myocardial function and contractility objectively. Non-Doppler 2D strain imaging is a relatively new technique that analyzes myocardial motion by digital tracking of speckles in high resolution dynamic ultrasonic images. Being angle-independent, this technique has shown significant promise in evaluation of myocardial dysfunction and segmental dyssynchrony of the LV. Data regarding accuracy, validity and clinical applications of this new modality is rapidly accumulating. However, 2D echo based strain analysis can only provide the information about the myocardial area within the scanning window. Dynamic heart function is a continuous interaction of linear and twisting motion in all three dimensions. Acquisition of 2D images with a static scanner can move myocardial tissue out of the scanning window during a cardiac cycle. This factor could result in erroneous strain computation due to in-plane decorrelation . Therefore, 2D echo based strain provides only a subjective assessment of the extent of myocardial dysfunction and is subject to errors, as well, due to through-plane myocardial motion. To avoid these limitations, high resolution 3D echocardiography has been introduced and tested for speckle-tracking based strain determination. The quantitative estimation of regional cardiac deformation from 3D image sequences would have important clinical implications. In this study, we sought to evaluate the feasibility of 3D echo based strain to delineate the extent of ischemic myocardial dysfunction.
METHODS
We studied five adult pigs of either sex that underwent midline sternotomy under anesthesia in a well equipped controlled animal surgery lab. The pericardium was incised vertically to expose their heart for high resolution ultrasound scanning directly from the surface of the heart. Vital signs and oxygen saturation were continuously monitored throughout the study. The left anterior descending coronary artery (LAD) was isolated from the vein and arbitrarily divided into three equal zones from the LV apex distally to the origin of the first diagonal branch proximally. Baseline 3D full volume image loops were acquired from the apex with an X7-2 probe on a Phillips IE33 ultrasound system. The LAD was occluded in the distal-most zone first and the visibly ischemic area, as shown by change in color, was measured and 3D full volume images acquired. The study was repeated after occluding the LAD in proximal zones. Images were analyzed offline in an envelope detected MatLab based program. Average image size was 192 x 237 x 214 voxels with 0.63 mm/voxel spatial and 20 volume/cycle temporal resolution.
Three-Dimensional Strain Maps Can Delineate the Extent of Ischemic Myocardial Dysfunction
Muhammad Ashraf, MD; Andriy Myronenko, MS; Xubo Song, PhD; Zhiwen Zhou, MD; Keith DesRochers, BA;
Uyen T. Truong, MD; David J. Sahn, MD, FASE
Oregon Health & Science University, Portland, OR
Analysis
Full volume 3D image loops were analyzed in a 3D speckle tracking program based on frame-to-frame volumetric non-rigid image registration. The deformation between adjacent frames was parameterized using free form deformation (FFD) maps based on B-splines. From the control point locations, the location of an arbitrary speckle target in the 3D volumes was derived through interpolation. The output of this algorithm is an estimation of the three components of a continuous displacement field as shown in 3D space at two viewing angles.
A full-volume 3D image acquired directly from the surface of heart in an open chest pig and processed for 3D strain in an envelope detected program.
Color-coded strain maps as derived from analysis of high-resolution 3D echocardiographic image loops.
RESULTS
Strain results were projected as color coded maps in a quantitative parametric display. Dysfunctional myocardial area was measured from the display in end-systolic frames. Extending the level of LAD ligation proximally also increased the size of the ischemic zone as measured from color change on the surface of the heart that correlated with the size of myocardial dysfunction as quantified from parametric strain maps from 3D image analysis.
Displacement Field
CONCLUSIONS
Quantitative 3D strain maps could provide an objective evaluation of myocardial dysfunction in coronary ischemia.