Recognizing the critical need for standardization in strain imaging, in 2010, the European Association of Echocardiography (now the European Association of Cardiovascular Imaging, EACVI) and the American Society of Echocardiography (ASE) invited technical representatives from all interested vendors to participate in a concerted effort to reduce intervendor variability of strain measurement. As an initial product of the work of the EACVI/ASE/Industry initiative to standardize deformation imaging, we prepared this technical document which is intended to provide definitions, names, abbreviations, formulas, and procedures for calculation of physical quantities derived from speckle tracking echocardiography and thus create a common standard.
Introduction
This document represents a consensus statement from the EACVI/ASE/Industry Task Force to standardize deformation imaging (‘the Task Force’) to communicate standard physical and mathematical definitions of various parameters commonly reported in myocardial deformation imaging. It is aimed primarily at the technical engineering community and also interested clinicians. The document is not intended to explore the wide range of clinical applications of deformation imaging.
There is a growing body of evidence showing that the assessment of myocardial deformation by Doppler or speckle tracking techniques provides incremental information in the clinical setting. Deformation imaging has been shown to provide unique information on regional and global ventricular function with some studies showing reduced inter- and intraobserver variability in assessing regional left ventricular (LV) function. The main areas of application of these techniques have been assessment of myocardial mechanics, ischaemic heart disease, cardiomyopathies, LV diastolic dysfunction, and in detecting subclinical myocardial dysfunction in patients undergoing chemotherapy for cancer or in those affected by heart valve diseases. Over the years, a number of software packages and algorithms have entered the market, but a practical limitation to the use of these techniques in routine clinical practice has been the significant variability that exists among vendors. Such a variability relates to several factors: differences in the terminology describing myocardial mechanics; the type of stored data which is used for quantitative analysis (e.g. proprietary formats vs. standard DICOM format); the modality of measuring basic parameters (tissue Doppler vs. speckle tracking); the definition of parameters (many vendors use proprietary speckle tracking algorithms or define different tracking regions for the same parameter); and the results output.
Recognizing the critical need for standardization in strain imaging, in 2010, the European Association of Echocardiography (now the European Association of Cardiovascular Imaging, EACVI) and the American Society of Echocardiography (ASE) invited technical representatives from all interested vendors to participate in a concerted effort to reduce intervendor variability of strain measurement.
As an initial product of the work of the EACVI/ASE/Industry initiative to standardize deformation imaging, we prepared this document which is intended to provide definitions, names, abbreviations, formulas, and procedures for calculation of physical quantities derived from speckle tracking echocardiography and thus create a common standard. This document is purely technical and provides technical information only. Therefore,
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It is not intended to provide information about the clinical relevance of different measurements.
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It is not intended to suggest which parameters a product should preferably include.
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It is not intended to favour speckle tracking over other approaches for the echocardiographic quantification of myocardial function, such as tissue Doppler, which can provide comparable parameters of comparable relevance.
By providing clear definitions of the standard quantities that any software solution should report, the differences among different products should be limited to:
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Technical: accuracy and reproducibility of the proprietary approach to speckle tracking;
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Marketing: choices about how and what different products report;
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Innovations: further parameters or representations beyond what is reported in this document.
Readers interested in a more in-depth description of the mathematics and physics are referred to the structural mechanics literature.
Geometry Definitions
Region of Interest
The complete myocardial region of interest (ROI, Figure 1 ) is defined at end-diastole by:
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Endocardial border: the inner contour of the myocardium;
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Epicardial border: the outer contour of the myocardium;
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Myocardial midline: the middle ROI axis defined in the middle between inner and outer ROI contours.
Each of these contours can be either user-defined or generated automatically. In any case, where they are generated automatically, the user should be allowed to check them and, if needed, edit them manually. Extreme care should be taken in the definition of ROI, as inclusion of pericardium will result in reduction of measured strain. Different generations of the software appear to have different ROI defaults, and lack of user interaction will contribute to measurement variation.
Endocardial measurements pertain to the behaviour of the endocardial border and are represented there. Midline measurements, when available, refer to the behaviour of the middle ROI axis and are represented there. Epicardial measurements pertain to the behaviour of the epicardial border and are represented there. In case of tracking results that represent the average of measurements obtained over the full myocardial thickness, these are typically represented with the mid-wall line specifying this full wall reference.
When the epicardial border is not drawn, then the measurements typically refer to the single endocardial border and are presented there.
Task force recommendation: The key requirement for any software solution is that it explicitly states what is being measured and the spatial extent (in pixels or millimeters) over which the data is sampled for a given ROI. Measurement definitions can be: endocardial, midline, epicardial, or full wall.
Segment Definitions
Segments are the anatomical units of myocardium for which the results of the various strain analysis will be reported.
Apical Views
Topographic definitions of the myocardial ROI in apical views are shown in Figure 1 , where:
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‘Left/right base’: end points of the endocardial border.
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‘Midbase’: midpoint between two basal end points of the endocardial border.
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‘Apex’: the most distant from ‘midbase’ or a manually defined endocardial point.
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‘Left/right ROIs’: ROI from the left/right base to apex.
The segments on the left and the right sides of the ROI are then defined such as to have the same end-diastolic length (the precise definition of end-diastole will be discussed below). Then, individual segments follow the underlying tissue and change their lengths during the various instants of the cardiac cycle. Thus, segmentation is performed as follows:
- •
Take the border at the user-defined or automatically selected frame,
- •
Define left and right ROIs,
- •
Divide each ROI into segments of equal length at the time point of end-diastole.
In the standard six-segment model (employed for global LV 16- or 18-segment models), the length of the three left segments is equal to the (left ROI length)/3, and the length of the three right segments is equal to (right ROI length)/3.
In case of a 17-segment model (which is not recommended for functional imaging, since the apical cap does not contract), the basal, mid, and apical segments have the length of 2/7th of the right and left ROI length, respectively, while the apical cap is composed of 1/7th of the right plus 1/7th of the left ROI.
Note that when segmental lengths are different, this fact must be taken into account when computing averages from segmental values.
Since the segments are presented with anatomical names corresponding to the LV wall the image refers to, it is necessary that the system recognizes or allows selection of the specific view under analysis. The system should also recognize or allow selection of whether an image is recorded as flipped left/right or inverted up/down.
Short-axis Views
Topographic definitions of the myocardial segments in short-axis views are shown in Figure 2 . These views are approached differently from apical views: segments should be defined by measuring the angle relative to a centre of cavity, and imposing equality of angle coverage instead of tissue length. Alternatively, segments may be defined as having an equal border length at the end-diastolic frame—in similarity to apical views. Depending on the segmentation model used, the apical short-axis ROI is subdivided into six or four segments ( Figure 3 ). The anterior insertion of the RV free wall is used as an anatomical reference.
Segmentation Models
Segmentation models are built to reflect coronary perfusion territories, to result in segments with comparable myocardial mass, and to allow comparison within echocardiography and with other imaging modalities. Accordingly, a 17-segment model is commonly used ( Figure 3 , central panel). The 16-segment model ( Figure 3 , left panel) divides the entire apex into four segments (septal, inferior, lateral, and anterior). The 18-segment model ( Figure 3 , right panel) divides the apex into six segments similar to the basal and mid-ventricular level. The last of these, the 18 segment model is simple and well suited to describe myocardial mechanics from two-dimensional (2D) data, but results in an overweighting of the apical-region (distal) myocardium in the overall score.
Task force recommendations: Segment definitions refer to the anatomy at the end-diastolic frame. If the segmentation is automatically proposed by the analysis software, a manual correction to modify the anatomy relative to the segments must be allowed to adjust for varying anatomy. Furthermore, the selection of a specific view, image inversion, or the possible left/right flip must be possible.
Geometry Definitions
Region of Interest
The complete myocardial region of interest (ROI, Figure 1 ) is defined at end-diastole by:
- •
Endocardial border: the inner contour of the myocardium;
- •
Epicardial border: the outer contour of the myocardium;
- •
Myocardial midline: the middle ROI axis defined in the middle between inner and outer ROI contours.
Each of these contours can be either user-defined or generated automatically. In any case, where they are generated automatically, the user should be allowed to check them and, if needed, edit them manually. Extreme care should be taken in the definition of ROI, as inclusion of pericardium will result in reduction of measured strain. Different generations of the software appear to have different ROI defaults, and lack of user interaction will contribute to measurement variation.
Endocardial measurements pertain to the behaviour of the endocardial border and are represented there. Midline measurements, when available, refer to the behaviour of the middle ROI axis and are represented there. Epicardial measurements pertain to the behaviour of the epicardial border and are represented there. In case of tracking results that represent the average of measurements obtained over the full myocardial thickness, these are typically represented with the mid-wall line specifying this full wall reference.
When the epicardial border is not drawn, then the measurements typically refer to the single endocardial border and are presented there.
Task force recommendation: The key requirement for any software solution is that it explicitly states what is being measured and the spatial extent (in pixels or millimeters) over which the data is sampled for a given ROI. Measurement definitions can be: endocardial, midline, epicardial, or full wall.
Segment Definitions
Segments are the anatomical units of myocardium for which the results of the various strain analysis will be reported.
Apical Views
Topographic definitions of the myocardial ROI in apical views are shown in Figure 1 , where:
- •
‘Left/right base’: end points of the endocardial border.
- •
‘Midbase’: midpoint between two basal end points of the endocardial border.
- •
‘Apex’: the most distant from ‘midbase’ or a manually defined endocardial point.
- •
‘Left/right ROIs’: ROI from the left/right base to apex.
The segments on the left and the right sides of the ROI are then defined such as to have the same end-diastolic length (the precise definition of end-diastole will be discussed below). Then, individual segments follow the underlying tissue and change their lengths during the various instants of the cardiac cycle. Thus, segmentation is performed as follows:
- •
Take the border at the user-defined or automatically selected frame,
- •
Define left and right ROIs,
- •
Divide each ROI into segments of equal length at the time point of end-diastole.
In the standard six-segment model (employed for global LV 16- or 18-segment models), the length of the three left segments is equal to the (left ROI length)/3, and the length of the three right segments is equal to (right ROI length)/3.
In case of a 17-segment model (which is not recommended for functional imaging, since the apical cap does not contract), the basal, mid, and apical segments have the length of 2/7th of the right and left ROI length, respectively, while the apical cap is composed of 1/7th of the right plus 1/7th of the left ROI.
Note that when segmental lengths are different, this fact must be taken into account when computing averages from segmental values.
Since the segments are presented with anatomical names corresponding to the LV wall the image refers to, it is necessary that the system recognizes or allows selection of the specific view under analysis. The system should also recognize or allow selection of whether an image is recorded as flipped left/right or inverted up/down.
Short-axis Views
Topographic definitions of the myocardial segments in short-axis views are shown in Figure 2 . These views are approached differently from apical views: segments should be defined by measuring the angle relative to a centre of cavity, and imposing equality of angle coverage instead of tissue length. Alternatively, segments may be defined as having an equal border length at the end-diastolic frame—in similarity to apical views. Depending on the segmentation model used, the apical short-axis ROI is subdivided into six or four segments ( Figure 3 ). The anterior insertion of the RV free wall is used as an anatomical reference.
Segmentation Models
Segmentation models are built to reflect coronary perfusion territories, to result in segments with comparable myocardial mass, and to allow comparison within echocardiography and with other imaging modalities. Accordingly, a 17-segment model is commonly used ( Figure 3 , central panel). The 16-segment model ( Figure 3 , left panel) divides the entire apex into four segments (septal, inferior, lateral, and anterior). The 18-segment model ( Figure 3 , right panel) divides the apex into six segments similar to the basal and mid-ventricular level. The last of these, the 18 segment model is simple and well suited to describe myocardial mechanics from two-dimensional (2D) data, but results in an overweighting of the apical-region (distal) myocardium in the overall score.
Task force recommendations: Segment definitions refer to the anatomy at the end-diastolic frame. If the segmentation is automatically proposed by the analysis software, a manual correction to modify the anatomy relative to the segments must be allowed to adjust for varying anatomy. Furthermore, the selection of a specific view, image inversion, or the possible left/right flip must be possible.
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