2.2. Echocardiographic studies and image acquisition
The device used for conventional 2DE and RT3DE was the Philips IE33 system with a matrix array ultrasonographic transducer (X4.1 transducer; Philips Medical Systems, Bothell, WA, USA). We used Simpson’s biplane method for measurement of ejection fraction with in an apical 4 and 2 chamber views according to recent guidelines (7). After endocardial tracing of borders at end systole and end diastole was performed, we calculated LVEF with the formula by using LV end-diastolic (EDV) and LV end-systolic volumes (ESV) as follows: EF = (EDV-ESV) ⁄ EDV.
To achieve optimal Real-time 3D echocardiographic acquisition of the left ventricle, images were optimized by managing the gain, compress, and time-gain compensation controls. Sector width and depth at two dimensional setting and we switched to xPlane imaging to detect the quality of endocardial borders at orthogonal view. After obtaining a satisfactory image which included all segments of myocardium clearly, full-volume acquisition with capturing of 4 adjacent ECG gated sub-volumes over 4 consecutive cardiac cycles in a pyramidal scan was performed during patients end-expiratory apnea within single breathhold to prevent stitching artifacts. Acquisition of each sub‐volume was triggered to the ECG R‐wave of every other heartbeat to allow sufficient time for the probe to be recalibrated and each subvolume stored.
Post processing analysis of volumes and EF were performed using Qlab software (Version 9.0; Philips Medical Systems) by two expert echocardiographer with extensive training in 3D echocardiography. The multiplanar view was aligned to maximize the LV cavity long- and short-axes in the 2- and 4-chamber views. End- diastole was defined as the first frame after mitral valve closure and end- systole was defined as the first frame after aortic valve closure. After first identifying the apex and mitral annulus on the end-diastolic and end-systolic frames, transverse plane was adjusted at the level of papillary muscles and saggital plane was adjusted from the midline of mitral annulus to apex. Then automatic endocardial border definition was performed by applying 4 mitral annular and 1 apical points: septal, lateral, anterior, inferior annular, and apex (Figure 1). Manual corrections of the LV endocardial borders including papillary muscles and trabeculations were performed if the operator judges the automatically detected surface as suboptimal. Sequence analysis were performed and checked for correct border detection frame- by- frame. At the end of analysis LVEDV, LVESV, LVEF, stroke volume, cardiac output, 16 segments and 12 segments SDI were obtained (Figure 2) (8).