Recording Wall Motion and Defining Endocardium
©Walter Rasmussen, R.D.C.S.
Analysis of left ventricular wall motion and endocardial borders requires attention to many of the imaging tips discussed in the physics section of this guide. Experimenting with Frequency, Focal Zone, adjusting the overall Gain, Dynamic Range, and processing tools such as UD Clarity, Line Density and others covered in the section, Tools for Maintaining Ultrasound Image Clarity can be used to accurately define the endocardial border.
As stated in the section on ultrasound physics, a video clip is best recorded while the heart is in a fixed position during the cardiac cycle. In some patients, this is not an issue, but when it is, unless the sonographer takes steps to assure that the heart is in a relatively stable position during clip acquisition the beginning and end of the clip will jump, making wall motion analysis considerably more difficult.
The best way to assure that the heart remains in a stationary position is by acquiring the clip at a resting point during respiration such as at the end of inspiration or the end of expiration. If, upon review of the clip, the desired effect is not achieved, the patient can be asked to suspend their breathing while the video clip is being recorded.
Capturing images in the retrospective mode and reviewing before saving has a great advantage for assuring the highest quality video clips because the technical problems associated with heart movement and incorrect triggering of the clip are managed as they occur. This saves time because the sonographer is less likely to have to re-position the patient and repeat a clip when reviewing the exam and making the final measurements prior to closing the study.
Techniques for defining Endocardium:
If, despite using respiratory maneuvers, changes in transducer position/angulation and focal zone, the endocardium is still difficult to see, the sonographer should experiment with lowering the frequency, adjusting the overall gain (higher) and dynamic range (lower), in order to render the clearest possible image of the border between endocardium and chamber. Some ultrasound machines can use the two-dimensional image combined with Doppler tissue imaging (DTI or TDI), or B-Color Imaging for visual enhancement of myocardial tissue, while other machines also have other adjustments that change persistence of the pixels, bridging the gaps between individual reflections. If the sonographer has access to a three-dimensional probe, it can sometimes produce an acceptable image of the left endocardial borders due to increased slice thickness. Some ultrasound machines have a two-dimensional imaging mode that increases slice thickness if a 3-D probe is used (Philips’ Elevation Compounding is an example).
In difficult situations, the value of off-axis views cannot be overemphasized. If the ultrasound can be made to bounce more directly off a surface that was poorly imaged in the original view, then it is worth the effort to make a supplemental clip that is off-axis. The advantage of this technique is that in most cases, through the use of multiple clips, some of which are off-axis, all of the wall segments can be recorded.