https://erp.bioscientifica.com/view/journals/echo/6/2/ERP-18-0068.xml
3D acquisitions in SE
The use of 3D echocardiography during SE reduces the time taken for image acquisition (58), improve foreshortened imaging planes (58) and increase reproducibility between imaging planes acquired at different stages of stress (59). New and relatively fast 3D ultrasound imaging devices are entering the market offering superior image quality, higher frame (3D volume) rates and ever-expanding capabilities that increase the potential for routine use.
Modes of 3D SE
3D systems offer several different imaging modes:
- Real-Time 3D (RT3D) Multislice Imaging. Detection of haemodynamically-significant CAD with RT3D relies on the detection of changes in wall motion and thickening between rest and peak stress in the same way as 2D SE. The availability of multislice and multiplane RT3D permits simultaneous viewing of standard parasternal long, parasternal short and apical volumetric data, such that specificity and accuracy may be better than 2D SE (60). In fact, any chosen imaging plane of the LV can theoretically be visualised allowing a more detailed wall motion analysis than is currently available from standard 2D imaging planes. This improves detection of wall motion abnormalities in the apical segments and allows off-axis images to be interrogated, while preserving overall accuracy (60). Moreover, since the whole LV is imaged simultaneously, image acquisition becomes greatly simplified and faster (61).
- Real-Time 3D Full Volume Data Acquisition (RT3DFV): With RT3DFV, full volume 3D datasets are acquired with the transducer positioned over the apex with the volume size adjusted to incorporate the entire left ventricle. Initial studies involving dobutamine stress echocardiography show shorter image acquisition times for 3D imaging than 2D imaging (62). There is no need to acquire parasternal images. As yet, data predominantly show equivalent overall accuracy compared to 2D SE with RT3DFV datasets (63).
3D volume data acquisition
The patient should be asked to stop breathing at end-expiration during the full volume acquisition to minimise issues with ‘fault lines’ between sub-volumes after reconstruction. Care should be given to ensure good-quality ECG gating and currently obtaining good-quality RT3DFV studies is difficult in patients with arrhythmias, particularly atrial fibrillation. With exercise SE, RT3DFV is more challenging and stitching artefacts due to hyperventilation and cardiac translation are more likely to occur, so much of the data acquired in existing publications relate to pharmacological stress.
In an otherwise suboptimal harmonic 3D SE study, LVO contrast has been shown to improve endocardial border delineation to a similar level to that achieved by contrast-enhanced 2D (64). A limitation to the use of LVO in 3D SE is that this does cause a reduction in temporal resolution (65). This has significance during peak exercise, when the heart rate is high and the number of 3D volumes per cardiac cycle is at levels that may be too low for diagnostic use.
Workflow and display
Present workflow issues for 3D stress analysis include cropping the 3D datasets to create a multiplane reconstruction equivalent to standard 2D image planes. However, this takes time and despite initially acquiring a 3D image, the time taken to create the necessary anatomical views may have an impact on the clinical workflow of SE. There are commercially available 3D stress software packages for processing 3D stress images that improve workflow, producing whole volume short axis slices for analysis. These derived 2D images can be ‘shuffled’ and displayed side by side for visual analysis in any format required. The key, however, to improving workflow for 3D SE will be the automation of the cropping and reconstruction process, and the quantification of LV wall motion and thickening.
