The variability of 2D and 3D transthoracic echocardiography applied in a general population : Intermodality, inter- and intraobserver variability

Assessment of the left ventricular (LV) function by three-dimensional echocardiography (3DE) is potentially superior to 2D echo echocardiography (2DE) for LV performance assessment. However, intra- and interobserver variation needs further investigation. We examined the intra- and interobserver variability between 2 and 3DE in a general population. In total, 150 participants from the Copenhagen City Heart Study were randomly chosen. Two observers assessed left ventricular ejection fraction (LVEF), end-diastolic (EDV) and end-systolic volumes (ESV) by 2DE and 3DE. Inter-, intraobserver and intermodality variabilities are presented as means of difference (MD), limits of agreement (LoA), coefficient of correlation (r), intraclass correlation coefficients (ICC). The lowest MD and LoA and highest r- and ICC-values was generally seen among the 3D acquisitions, with the 3D EDV interobserver as the best performing estimate (r = 0.95, ICC = 0.94). The largest MD, LoA and lowest r- and ICC-values was found in the interobserver 2D LVEF (r = 0.76, ICC = 0.63. For the intraobserver analysis, there were statistically significant differences between observations for all but 3DE EDV (p = 0.06). For interobserver analysis, there were statistically significant differences between observers for all estimates but 2DE EDV (p = 0.11), 3D ejection fraction (p = 0.9), 3DE EDV (p = 0.11) and 3D ESV (p = 0.15). Three-dimensional echocardiography is more robust and reproducible than 2DE and should be preferred for assessment of LV function.

High frame rate multi-perspective cardiac ultrasound imaging using phased array probes

Ultrasound (US) imaging is used to assess cardiac disease by assessing the geometry and function of the heart utilizing its high spatial and temporal resolution. However, because of physical constraints, drawbacks of US include limited field-of-view, refraction, resolution and contrast anisotropy. These issues cannot be resolved when using a single probe. Here, an interleaved multi-perspective 2-D US imaging system was introduced, aiming at improved imaging of the left ventricle (LV) of the heart by acquiring US data from two separate phased array probes simultaneously at a high frame rate. In an ex-vivo experiment of a beating porcine heart, parasternal long-axis and apical views of the left ventricle were acquired using two phased array probes. Interleaved multi-probe US data were acquired at a frame rate of 170 frames per second (FPS) using diverging wave imaging under 11 angles. Image registration and fusion algorithms were developed to align and fuse the US images from two different probes. First- and second-order speckle statistics were computed to characterize the resulting probability distribution function and point spread function of the multi-probe image data. First-order speckle analysis showed less overlap of the histograms (reduction of 34.4%) and higher contrast-to-noise ratio (CNR, increase of 27.3%) between endocardium and myocardium in the fused images. Autocorrelation results showed an improved and more isotropic resolution for the multi-perspective images (single-perspective: 0.59 mm × 0.21 mm, multi-perspective: 0.35 mm × 0.18 mm). Moreover, mean gradient (MG) (increase of 74.4%) and entropy (increase of 23.1%) results indicated that image details of the myocardial tissue can be better observed after fusion. To conclude, interleaved multi-perspective high frame rate US imaging was developed and demonstrated in an ex-vivo experimental setup, revealing enlarged field-of-view, and improved image contrast and resolution of cardiac images.

Multi-View 3-D Fusion Echocardiography: Enhancing Clinical Feasibility with a Novel Processing Technique

A novel system for fusing 3-D echocardiography data sets from complementary acoustic windows was evaluated in 12 healthy volunteers and 12 patients with heart failure. We hypothesized that 3-D fusion would enable 3-D echocardiography in patients with limited acoustic windows. At least nine 3-D data sets were recorded, while three infrared cameras tracked the position and orientation of the transducer and chest respiratory movements. Corresponding 2-D planes of the fused 3-D data sets and of single-view 3-D data sets were assessed for image quality and compared with measurements of left ventricular function obtained with contrast 2-D echocardiography. The signal-to-noise ratio in accurately fused 3-D echocardiography recordings improved by 55% in systole (p < 0.001) and 47% in diastole (p < 0.00001) compared with the apical single-view recordings. The 3-D data sets acquired during short breath holds were successfully fused in 11 of 12 patients. The improvement in endocardial border definition (from 11.7 ± 6.0 to 24.0 ± 3.3, p < 0.01) enabled quantitative assessment of left ventricular function in 10 patients, with no significant difference in ejection fraction compared with contrast 2-D echocardiography. In patients with heart failure and limited acoustic windows, the novel fusion protocol provides 3-D data sets suitable for quantitative analysis of left ventricular function.

Multiview Three-Dimensional Echocardiography Image Fusion Using a Passive Measurement Arm

Three-dimensional (3D) echocardiography offers a fast and efficient way to scan and assess the structures and function of the heart. However, due to limitations inherent to 3D echocardiography such as limited field-of-view and low signal-to-noise ratio, 3D assessment of the heart is performed only in a minority of patients who undergo transthoracic echocardiography. One approach for improving the field-of-view and image quality is to scan the heart from multiple locations by moving the transducer and fusing the resulting images into a single volume, which requires 3D alignment of individual volumetric echocardiography scans. Previous approaches relied on optical or electromagnetic trackers for transducer tracking. This study proposes a passive measurement arm system for tracking the position of the ultrasound transducer and thereby aligning multiple echocardiography scans. The proposed system does not suffer from line-of-sight limitation as in the case of an optical tracking based fusion system. Additionally, in contrast to an electromagnetic based tracking system, measurement arm measurements are not affected by other ferromagnetic materials in the vicinity. The proposed approach was tested by scanning a heart phantom and fusing nine echocardiography volumes acquired from different locations. The fusion of all nine scans yielded a percentage field-of-view improvement of 98.5%.

Patient movement compensation for 3D echocardiography fusion

Limited field of view (FOV) is a major problem for 3D real-time echocardiography (3DRTE), which results in an incomplete representation of cardiac anatomy. Various image registration techniques have been proposed to improve the field of view in 3DRTE by fusing multiple image volumes. However, these techniques require significant overlap between the individual volumes and rely on high image resolution and high signal-to-noise ratio. Changes in the heart position due to patient movement during image acquisition can also reduce the quality of image fusion. In this paper, we propose a multi-camera based optical tracking system which 1) eliminates the need for image overlap and 2) compensates for patient movement during acquisition. We compensate for patient movement by continuously tracking the patient position using skin markers and incorporating this information into the fusion process. We fuse volumes acquired during R-R wave peaks based on Electrocardiogram (ECG) data to account for retrospective image acquisition. The fusion technique was validated using a heart phantom (Shelley Medical Imaging Technologies) and on one healthy volunteer. The fused ultrasound volumes could be generated in within 2 seconds and were found to have complete myocardial boundaries alignment upon visual assessment. No stitching artefacts or movement related artefacts were observed in the fused image.

Multiview 3-D Echocardiography Fusion with Breath-Hold Position Tracking Using an Optical Tracking System

Recent advances in echocardiography allow real-time 3-D dynamic image acquisition of the heart. However, one of the major limitations of 3-D echocardiography is the limited field of view, which results in an acquisition insufficient to cover the whole geometry of the heart. This study proposes the novel approach of fusing multiple 3-D echocardiography images using an optical tracking system that incorporates breath-hold position tracking to infer that the heart remains at the same position during different acquisitions. In six healthy male volunteers, 18 pairs of apical/parasternal 3-D ultrasound data sets were acquired during a single breath-hold as well as in subsequent breath-holds. The proposed method yielded a field of view improvement of 35.4 ± 12.5%. To improve the quality of the fused image, a wavelet-based fusion algorithm was developed that computes pixelwise likelihood values for overlapping voxels from multiple image views. The proposed wavelet-based fusion approach yielded significant improvement in contrast (66.46 ± 21.68%), contrast-to-noise ratio (49.92 ± 28.71%), signal-to-noise ratio (57.59 ± 47.85%) and feature count (13.06 ± 7.44%) in comparison to individual views.