1. Sreyas Ravi; Austin Park; Muhammad Ashraf, MD; David J. Sahn, MD, FASE
ABSTRACT
Background: Radial strain is an important index of myocardial function. 2D echo research on cardiac strain has verified speckle tracking for assessing cardiac mechanics despite lost information from out of plane motion. This study tested whether a novel 4D echo image-based 3D-Wall Motion Tracking (3D-WMT) program is capable of accurately measuring radial strain. Methods: A custom pulsatile pump apparatus drove each phantom heart model with constant rotation (5 degrees) and compaction (10 mm) to simulate physiological cardiac motion. Stroke volumes used were 30, 40, 50, 60, and 70 ml. A latex balloon was sutured into the LV of five adult porcine hearts. The hearts were fixed to a rotating plate at the base and lightly fixed at the apex. The model was submerged in a water tank with the Toshiba matrix array PST-25SX 2.5-MHz transducer. Sonomicrometry (sono) crystals were sutured into the epicardium and on the endocardium adjacent to the LAD. Full volume data was acquired for all stroke volumes and analyzed by Toshiba 3D-WMT. Results: Linear regression analysis suggests a strong correlation between sono data and 3D-WMT derived strain values, with a high correlation coefficient for radial strain (R² =.759). The P-value was less than Bland-Altman analysis revealed a slight overestimation of strain values. Conclusions: The results suggest that Toshiba 3D-WMT can be used to study radial strain.
CONCLUSIONS
This was a validation study to determine the accuracy and efficacy of the Toshiba 3D-WMT strain-determination in quantifying RS in a beating-heart model. The results suggest that the Toshiba 3D-WMT can accurately measure radial strain, though values were consistently higher than the sonomicrometry. The beating-heart model introduced compaction and rotation, which are components of the cardiac mechanics of contraction.
A future study is proposed to validate the accuracy of Toshiba 3D-WMT in detecting changes in strain after a simulated myocardial infarction, which would have important clinical applications to assess damage to cardiac tissue after myocardial infarctions.
DISCLOSURES
No relationships to disclose:
Rosie Bleck Kacie Amacher
Meihua Zhu Cole Streiff
Sumito Kimura Sreyas Ravi
Austin Park Muhammad Ashraf
David J. Sahn
BACKGROUND
METHODS
Five freshly harvested pig hearts were studied. Each heart was fixed to a rotating plate at the base and lightly fixed at the apex to model twisting heart motion. A latex balloon over a tube was secured into the LV cavity by stitching at mitral annulus, and connected to a calibrated pulsatile pump, for pulsatile motion. The model was submerged in a water tank to facilitateUltrasound scanning, with the Toshiba matrix array PST-25SX 2.5-MHz transducer fixed near the apex. Two Sono crystals were sutured, one at epicardium and one at endocardium of LV adjacent to the LAD.
Pulsatile motion of heart was generated at different pumped stroke volumes (30, 40, 50, 60, and 70 ml) at a constant rotation (5 degrees) and compaction (10 mm) to simulate physiological cardiac motion. Full volume data was acquired by a Toshiba Artida ultrasound system (Toshiba Medical Systems, Tochigi, Japan). The 4D images were analyzed by Toshiba UltraExtend 3D-Wall Motion Tracking (3D-WMT), focusing on the Mid Anterior segment of the heart.(Figure 2) Strain measurements from the sono data were computed using a custom software. The echo derived strain values from Toshiba ultrasound system and analysis software were compared to sono derived strain measurements. .
Radial Strain Determination from 4D Echocardiographic Volumes Using 3D-Wall Motion Tracking
Rosie Bleck, BA; Kacie Amacher, BA; Meihua Zhu, MD, PhD; Cole Streiff, BA; Sumito Kimura, MD;
Sreyas Ravi; Austin Park; Muhammad Ashraf, MD; David J. Sahn, MD, FASE
Oregon Health & Science University, Portland, Oregon
RESULTS
Linear regression analysis suggested a strong correlation between sonomicrometry derived strain measurements and the Toshiba 3D-Wall Motion Tracking derived strain values. A high correlation coefficient for radial strain (R² =.759) was found. The P-value verified these results, and was less than .001 (top graph, Figure 3) Bland-Altman analysis showed that 100% of the data was within a 95% Confidence Interval for RS. A slight consistent overestimation by the Toshiba 3D-WMT system was observed, but the strong linear correlation suggests that the Toshiba Artida ultrasound imaging system and the Toshiba UltraExtend 3D-Wall Motion Tracking software accurately quantified radial strain, despite this constant overestimation (bottom graph, Figure 3).
Accurate quantification of left ventricular function is important in clinical decision-making and follow-up assessment. The evaluation of abnormalities of left ventricular (LV) function by qualitative estimation of wall thickening (WT) is routinely performed during stress echocardiography, but is highly subjective and requires a high level of expertise to obtain correct readings.
New speckle-tracking based strain analysis enables objective evaluation of the all three components of myocardial deformation including myocardial thickening. Strain Imaging, therefore, is evolving as a mature tool for accurate and more reliable non-invasive assessment of cardiac mechanics. Speckle tracking derived radial strain (RS) is measure of myocardial thickening during systole and is suggested an important index of myocardial function. Although two-dimensional (2D) strain has been shown to be accurate in the detection of contraction changes in different clinical conditions including myocardial ischemia and dobutamine infusion for stress testing, out of plane myocardial motion during 2D scanning is suggested a potential source of error in strain computation.
Recent improvements in resolution quality of 4D Echocardiography images has allowed tracking speckles in 3D volumes for accurate assessment of myocardial deformation, avoiding any through plane motion. We sought to test the accuracy of Toshiba's Artida Ultrasound system and 3D-WMT software in radial strain determination.
Figure 1. Experimental Setup
Figure 2. Toshiba 3D-WMT UltraExtend software analysis of ultrasound images of the LV for strain determination
Figure 3. Linear Regression analysis of Toshiba 3D-WMT compared to sono derived strain values (Top) and Bland-Altman Analysis (bottom)