1. Using 4D Nongated Echocardiography
ABSTRACT
Background: The non-gated 4D echocardiogram is the most recently developed tool for visualizing cardiac mechanics without the requisite use of electrocardiogram (EKG) wires. This study was designed to determine the left ventricular (LV) stroke volume (SV) and mass (LVM) of fetal heart models using non-gated 4D echo. Methods: 4D volumes of fetal heart models (rabbit LVs) were acquired at five different stroke volumes (SV) between 1 and 5mL with an X6-1 matrix transducer interfaced with a Philips® iU22 ultrasound system. Data was collected at two different stroke rates (SR), 40 and 80 strokes per minute, for each SV and analyzed offline with QLab®. LVM and SV were calculated in QLab® according to stacked endocardial and epicardial ellipses and compared to displacement data. Results: We found no significant difference between the displacement and 4D echo-derived values for LVM (R2=0.98, p<0.01) and SV (R2=0.92, p<0.01). It was also determined that 97% of the data was contained within a 95% confidence interval (CI) in a Bland-Altman analysis. Conclusions: Thus, we determined that the new Philips® iU22 4D echocardiogram is an accurate way to measure the LV mass and SV of fetal hearts.
CONCLUSIONS
Thus, we determined that the new Philips® iU22 4D echocardiography derived measurements of SV and LVM are accurate for fetal sized hearts. Analysis of volume loops acquired from the same experimental state suggested that this image acquisition and analysis system was capable of a high level of precision. We look forward to increases in temporal resolution and feature tracking to improve the utility of this technology in the clinical analysis of fetal heart function.
DISCLOSURES
No relationships to disclose:
Kevin Truong Kaavya Mandi
Christine Kang Meihua Zhu
Muhammad Ashraf Cole Streiff
David J Sahn
REFERENCES
Kautzner, J., & Peichl, P. (2008). 3D And 4D Echo—applications In EP Laboratory Procedures. Journal of Interventional Cardiac Electrophysiology, 22(2),
Yagel, S., Cohen, S., Shapiro, I., & Valsky, D. (2007). 3D and 4D ultrasound in fetal cardiac scanning: a new look at the fetal heart. Ultrasound Obstet Gynecol, 29,
BACKGROUND
Echocardiography is extensively used in clinical practice to evaluate cardiac anatomy and function. Cardiac motion results in myocardial tissue movement outside of a static 2D imaging plane over the course of a cardiac cycle, and is considered a major source of error for quantitative evaluation of heart function.
Recent advances in medical imaging have made it possible to acquire full volume dynamic 3D image loops of the heart (Kautzner, et al., 2008). However, to improve the frame rate of 3D echo of a beating heart, an EKG signal is used to stitch multiple pyramidal volumes together. Poor quality of an EKG signal may limit the ability of software to stitch together 3D volumes. Lack of EKG signal limits application of this new 4D imaging technology in Fetal echocardiography.
A new 4D imaging method is developed recently, which allows acquisition of high frame rate 4D images without the use of EKG gating. Since it does not require EKG, this 4D echo may prove useful for acquiring image loops of fetal hearts. We sought to test this new imaging modality in a controlled phantom study for measuring stroke volume (SV) and left ventricular mass (LVM) in freshly harvested fetal sized rabbit hearts.
METHODS
We studied ten freshly harvested rabbit hearts. The right ventricle of each rabbit heart was removed and the aorta was sutured shut. A balloon was inserted into the LV through the mitral annulus and then attached to a Harvard pulsatile pump apparatus.
The heart was immersed in a water bath and fixed in place (Figure 1). The stroke volume was set to 1 mL and the stroke rate was set to 40 beats per minute (BPM). The pump was turned on and two image loops were acquired. The stroke rate was then switched to 80 BPM and two additional volumes were acquired. This process was then repeated for stroke volumes of 2mL, 3mL, 4mL, and 5 mL.
All echo data was downloaded to QLab for analysis. Echo-derived SV and LVM values were compared against fluid displacement values at each state.
Image-Based Validation of Left Ventricular Mass and Stroke Volume in Fetal Sized Hearts
Using 4D Nongated Echocardiography
Kevin Truong; Kaavya Mandi; Christine Kang; Meihua Zhu, MD, PhD; Muhammad Ashraf, MD;
Cole Streiff, BA; David J Sahn, MD, FAHA
Oregon Health & Science University, Portland, OR, USA
RESULTS
Image data was analyzed offline in the QLab software. The endocardial and epicardial borders were user-defined at end diastolic (ED) and end systolic (ES) frames. The stroke volume was determined by the difference of the endocardial volumes at ED and ES. The LVM was determined by the difference in the epicardial and endocardial volumes at ED. This value was then multiplied by the density of cardiac tissue (1.053 g/mL). No significant difference was found between the displacement and 4D echo-derived values for LVM (p<0.01) and SV (p<0.01). Linear regression analyses reveal excellent agreement between both methods for SV and LVM (R2=0.92 and R2=0.98 respectively) as can be seen in Figures 3 and 4. Bland-Altman analyses revealed 97 percent of our data to be within limits of agreement.
Figure 1: Experimental Set up
Figure 2: Analysis in QLab
Figure 3: Linear-Regression Analysis of SV
Figure 4: Linear-Regression Analysis of LVM