1. Meihua Zhu, MD, PhD; Muhammad Ashraf, MD
ABSTRACT
Background: Strain determination in fetal hearts could provide important clinical information. We tested a new non-gated 4D echocardiography method for accuracy in strain computation. Methods: Fifteen rabbit hearts were studied. Each heart was mounted in a water tank to facilitate ultrasound scanning, connected to a calibrated pump by a balloon sutured into the left ventricle (LV), and pumped at stroke volumes (SV) 1-5 ml and stroke rates (SR) 40 and 80 bpm. Three 0.7mm sonomicrometry crystals were secured within the myocardium to record longitudinal and circumferential strain measurements. At each SV and each SR, 4D images were obtained by an X6-1 probe on a Philips iU22 ultrasound system while sonomicrometry displacement was recorded. This process was done before and after a simulated myocardial infarction (MI). 4D images were analyzed offline for strain by a MatLab-based program. Results: Data collected on the Philips ultrasound system correlated with sonomicrometry derived strain at each SV (CS: R² = 0.91, p<0.05; LS: R² = 0.87, p<0.05). A decrease in strain post-MI was detected by both echocardiography and sonomicrometry. Conclusions: Non-gated 4D echocardiography is a feasible method for strain determination of fetal hearts.
CONCLUSIONS
Non-gated 4D echocardiography is a feasible for computing strain fetal sized hearts.
DISCLOSURE
No relationships to disclose:
David J. Sahn Angela Han
Lydia Tam Vineet Apte
Zhijun Zhang Meihua Zhu
Muhammad Ashraf
BACKGROUND
4D Echocardiography is most recent development in real time cardiac imaging that is rapidly finding applications in clinical imaging of heart.
It offers excellent visualization of cardiac chambers and valves through enhanced three dimensional displays. It also has been shown to provide superior assessment of ventricular volumes and ejection fraction by eliminating the need of geometrical assumptions with 2D echo.
Despite some concerns about relatively lower spatio-temporal resolution as compared to 2D Echo, it is suggested a better way of computing speckle tracking based mechanical function by eliminating errors due to through plane motion.
Fetal Echocardiography is a routinely performed imaging study to screen or diagnose congenital Heart disease. Until recently the non-availability of EKG signal from fetus was major limitation in 4D imaging of fetal heart. Recently a new matrix probe is designed for an obstetric ultrasound system, which is also capable of 4D imaging of fetal heart without an EKG signal from fetus. By using a new spatiotemporal imaging correlation (iSTIC) technology with 4D Echocardiography, acquisition of a heart’s volume has become easier without EKG signal.
Image derived strain determination in fetal hearts could provide important clinical information about dynamic heart function. We tested the feasibility of using new non-gated 4D echocardiography image loops for strain computation in a controlled experimental study.
METHODS
The study was conducted on fifteen freshly harvested rabbit hearts for their smaller size to simulate fetal hearts. Each rabbit heart was attached to a calibrated pump by a balloon into the left ventricle (LV), secured at mitral annulus. Three 0.7mm sonomicrometry crystals were secured into the myocardium to record longitudinal and circumferential displacement.
Pulsatile motion was generated in LV by pumping a known stroke volumes (SV) at a known stroke rate. (SR). Model was placed in a water tank to facilitate ultrasound scanning, Four-D images were acquired on Philips iU22 ultrasound system using an X6-1 probe , and sonomicrometry displacement data recorded at five different SVs (1-5ml) and two different stroke rates (40 & 80 bpm).
After acquiring baseline data, myocardial infarct was simulated by injecting glutaraldehyde into LV wall. The study was repeated to acquire 4D echo and sono data at same SVs and SRs. Sonomicrometry and 4D image data was analyzed offline for strain by a MatLab-based program.
Evaluation of Circumferential and Longitudinal Strain in a Rabbit Fetal Heart Model Using 4D Echocardiography
David J. Sahn, MD, MACC; Angela Han; Lydia Tam; Vineet Apte; Zhijun Zhang, PhD;
Meihua Zhu, MD, PhD; Muhammad Ashraf, MD
Oregon Health & Science University, Portland, OR, USA
RESULTS
Increasing pumped volume increased stretching of myocardial tissue, which was detected as well correlated increases in longitudinal strain both by sonomicrometry and 4D Echo based strain method.
Sonomicrometry derived strains showed a good correlation with 4D Echo derived strains at all SVs studied (CS: R² = 0.91, p<0.05; LS: R² = 0.87, p<0.05).
A significant decrease in strain was detected in simulated infarct by both echocardiography and sonomicrometry.
Our strain results are derived from a pumped heart model passively driven at stroke rate of 40-89/min. Current maximum frame rate of this new 4D Fetal Echo system may not be optimal for strain analysis on images from a fetal heart beating at higher rates.
Off line processing of 4D echo data for strain computation
4D imaging of a pulsatile rabbit heart model 10 20 30 40 50 60 70 80 90
100
-0.1
-0.08
-0.06
-0.04
-0.02
0.02
Strain Curves at different Stroke Volumes