Real-time 3-dimensional transesophageal echocardiography (3DTEE, iE33, Philips Medical Systems, Andover, MA) is increasingly used in the setting of cardiac surgery. A growing body of evidence suggests the advantage of real-time 3DTEE over conventional 2DTEE for the diagnosis of cardiac pathologies and for decision making in a variety of clinical settings.1–6 The usefulness of 3DTEE is particularly noteworthy in mitral valve (MV) repair. Mitral regurgitation derives from a complex spectrum of dysfunctions. From a research standpoint, 3DTEE reveals aspects of mechanics and physiology useful for developing new approaches to repair.7,8 From a clinical operations perspective, complex leaflet defects are more readily appreciated by experts and nonexperts alike when observed in 3D.
In the current real-time 3DTEE, both conventional 2D and 3D images can be obtained using the same matrix array probe (X7-2t, Philips). Because these 2 modes differ with respect to handling of the datasets, new basic knowledge and skills are required for echocardiographers to efficiently manipulate the 3D image dataset intraoperatively. Full-volume (FV) 3D imaging is a mode in which 4 to 7 wedge-shaped, gated subvolume datasets are obtained and reconstructed into a large pyramid-shaped 3D image displayed at a relatively high frame rate.4 A single FV dataset contains more information than that obtained from other real-time 3D imaging modes. The FV dataset can be used to analyze left ventricular (LV) volume and MV geometry using plug-in software (QLAB and MVQ, respectively; Philips) installed on the echo machine.6 Information of multiple aspects can be obtained by freely rotating the dataset to view from any orientation. Additionally, valuable information can be obtained by cropping unwanted portions of the 3D dataset using 3 pairs (green, red, and blue) of planes that move along the 3D axes (fixed box cropping) or a plane that can be placed in any desired position (arbitrary plane cropping).3 An important feature of the current real-time 3DTEE system is that the orthogonal axes in each 3D image are set automatically according to the X-Y axes of the initial multiplane 2DTEE image, and therefore axis orientation of the 3D dataset differs depending on the initial 2D plane angle. See, for example, the difference in orthogonal axes and box-crop plane alignment between FV datasets obtained with the midesophageal (ME) 4-chamber (4C) view (panels A and B) and those obtained with the ME mitral commissural (MC) view (panels C and D) in Figure 1.
Intuitively, most echocardiographers acquire the initial FV3D datasets with the ME4C view, because it is a “gold standard” 2DTEE image.9 Other analogues of standard 2DTEE images, however, are difficult to obtain using this 3D dataset. In the 4CFV dataset, box crop planes are aligned to “obliquely” cross the MV or aortic valve (AV) (Fig. 1B). Except for the ME4C and ME2C views, the sectional images obtained using the box-cropping planes are not clinically relevant (Fig. 2). Although analogues of standard 2DTEE views can be obtained using the arbitrary plane-cropping process, the process is time consuming and the image orientation of the cropped images is difficult for other echocardiographers or trainees to envisage. Because of the complexity involved in handling the image datasets, the information contained within a single dataset is not fully used. Instead, multiple 3D datasets concerning the same cardiac structures within a variety of orthogonal axes are obtained as part of a single 3DTEE study. This is quite time consuming and imposes an additional workload on the perioperative echocardiographer. There has been no standardized scanning method for real-time 3DTEE. We therefore developed a comprehensive acquisition approach, bicommissural FV (BCFV) data acquisition, to maximize the information obtained about the cardiac anatomy within the dataset and to simplify the complex cropping process.
Our BCFV acquisition can be accomplished as follows:
- Obtain a 2D ME MC view.
- Press the Full volume button in the console, and a preview of the 2D ME MC and LV long-axis views are displayed in the left and right panels, respectively (Fig. 3).
- Adjust the scan area by turning the Image priority knob to include the AV and the entire MV. Scan depth can be set to include the whole LV (complete BCFV) or reduced to the level of the papillary muscles (shallow BCFV).
- Adjust the probe position (e.g., retroflex) so that the LV apex is aligned to the center of the sector.
- Acquire FV data, which displays as a 3D image oriented in the initial plane. Press the Reset crop button to display an uncropped FV image.
In the uncropped BCFV dataset, the heart is aligned in the crop box with en face view of the AV and MV through the front (green) and top (blue) cropping planes, respectively (Fig. 1, C and D). Furthermore, box cropping of the dataset by turning the plane adjustment knob yields many useful sectional images in addition to the analogues of standard 2DTEE views (Fig. 4, Table 1). The 3 pairs of cropping planes can be used as “windows” through which the 3D cardiac anatomy can be efficiently analyzed from a single 3D dataset. Cropping the dataset using the red planes shows sagittal cuts of mitral anterior–posterior leaflets, which allows for assessment of the coaptation of the anterior and posterior segments of the mitral leaflets (Fig. 4). The shallow BCFV dataset provides images of the MV and AV at a higher frame rate and is also useful for quantifying the 3D variables of the MV structure using MVQ software. The reference points required for MV modeling (anterior, posterior, anterolateral, and posteromedial edges of the mitral annulus, papillary muscles, and the AV) are prealigned in the windows of the multiplanar reformatting display (Fig. 5).
The advantage of this method is that a single dataset can be used with minimal manipulation for simple on-cart analysis of cardiac structures from multiple aspects. Because the direction of each cropping plane's movement is fixed, a comprehensive, reproducible assessment is possible using datasets acquired from different patients. Standardizing the 3D alignment of the heart may allow different echocardiographers to easily understand image orientation in similar 3D datasets. As shown in Figure 1C, the AV is critical to image orientation and is readily apparent in this 3D dataset. The sectional images of the LV system obtained using the green, red, and blue cropping planes by our method can be simulated as the sagittal, coronal, and axial sections of the LV system (thus cardiac axis oriented), respectively. It is interesting to note that the LV system (AV, left ventricle, papillary muscles, and MV) set in our present orthogonal axis alignment appears to be a single apparatus, like a teapot, that has a symmetric property, with the LV long-axis plane as a midline. Our speculation is supported by the fact that images obtained using the 2 red crop planes provide the mirror images of each other (panels E and F versus panels H and I in Fig. 4, respectively). Further anatomic investigation is necessary to validate our speculation.
Despite its usefulness, there are several limitations to the present method. First, the image quality of the FV dataset depends on electrocardiogram gating and thus may not be useful in patients with arrhythmia. Second, this method is not suitable for intraoperative real-time monitoring during surgical procedures because the FV 3D mode is not a “true” real-time 3D image modality. Third, a large part of the interatrial septum is out of the scan area of the BCFV dataset, requiring a different approach for analysis of the interatrial septum. Fourth, our method is exclusively applicable to the current Philips real-time 3DTEE system, which is the only real-time 3DTEE imaging modality currently available, and therefore it is not clear whether our technique can be applied to future real-time 3DTEE imaging modalities. The mitral anterior–posterior and mitral bicommissural lines, however, should be recognized by any cardiac imaging modality as the fundamental axes for evaluating LV morphology.
We present a useful method to obtain a single FV dataset that allows for efficient assessment of cardiac structures in real-time 3DTEE. The mitral bicommissural region, mitral anterior–posterior axes, and the line that connects the mitral annular center with the LV apex appear to be the key axes for 3D assessment of the cardiac morphology in a geometry-oriented manner. Further investigation to assess the feasibility of our method across patients with a variety of cardiac diseases is necessary.
Name: Yuji Hirasaki, MD.
Contribution: This author helped design the study and write the manuscript.
Attestation: Yuji Hirasaki approved the final manuscript.
Name: Yusuke Seino, MD.
Contribution: This author helped write the manuscript.
Attestation: Yusuke Seino approved the final manuscript.
Name: Yuko Tomita, MD.
Contribution: This author helped write the manuscript.
Attestation: Yuko Tomita approved the final manuscript.
Name: Minoru Nomura.
Contribution: This author helped write the manuscript.
Attestation: Minoru Nomura approved the final manuscript.
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