1. 2D Strain/Motion Anaylsis Program: An In Vitro Study
ABSTRACT
Background: Normal LV contraction involves a twisting component, the unwinding of which is an important contribution to early diastolic filling. Methods: We used a variable speed motor to rotate a thin plastic rod in a water bath. A continuous layer of beef was wrapped around this rod as a twist phantom. Tension in the roll increased slightly during rotation. Short axis 2D and tissue Doppler images were acquired using a GE/VingMed Vivid 7 at 3.5 MHz and >100frames/sec. Seven different speeds (20-80 cycles/min of winding and unwinding) were studied at two angles of rotation (45º & 90º). Data was analyzed offline on EchoPac® for tissue Doppler based strain and a new 2D strain rate (2DSR) program embedded in EchoPac®. Results: The 2DSR program tracked torsion well at 45° (mean determination = 49.4° ± 2.2°[SD]), while it underestimated the 90° twist computation (mean = 68.6° ± 15.5°), more at the highest twist rates. Tissue Doppler based SRI could not effectively define twist consistently. An inner to outer deformation gradient during twisting could be detected by tissue Doppler based SRI but clearer, less noisy determinations for this gradient were computed by the 2DSR method. Conclusions: The 2DSR program was more effective for detecting twist, especially because targets move across the sector, crossing scan lines of differing resolution during rotational movement.
Tissue Doppler based SRI could not effectively define twist consistently (Figure 4).
An outer to inner deformation gradient during twisting could be detected by tissue Doppler based SRI but clearer, less noisy determinations for this gradient were computed by the 2D method (Figure 5).
Figure 4. Tissue Doppler based strain
Figure 5. 2D Strain
CONCLUSIONS
The 2D program was more effective for detecting twist, because of its ability to measure orthogonal vectors. The 2D method underestimated the 90° twist, probably because it leads to major decorrelation between frames. This higher degree of twist, however, does not exist in vivo.
DISCLOSURE
No relationships to disclose:
Muhammad Ashraf
Monica T. Young
Amariek J. Jensen
James Pemberton
Occasional consultant to GE Medical Systems:
David J. Sahn
BACKGROUND
Cardiac twist is an important component of ventricular motion. It is responsible for 60% of the ejection fraction, with only 15% muscle shortening. Similarly, active unwinding of this twist plays an important role in achieving rapid early diastolic filling. This twist is explained by a spiral arrangement of myocardial fibers, as proposed by Torrent-Guasp and defined by MRI studies (Figure 1). Tracking myocardial twist, therefore, can provide important clinical information about fiber orientation which may be distorted in disease.
In rotation, targets move across the sector, crossing scan lines of differing resolution. This factor limits the ability of the tissue Doppler based method, because it analyzes only those components of deformation that are parallel to the scan line.
The 2D method, however, is based on speckle tracking using 2D gray scale images. 2D-velocity vector is estimated as a shift of speckle divided by time between successive frames.
Figure 1. Myocardial fiber orientation as proposed
by Torrent-Guasp
The computer automatically selects suitable rectangular blocks of tissue for searching the new location of block in the next frame using SAD (sum of absolute differences).
This method has the advantage of high frame rate with ability to measure orthogonal vectors. This factor makes it relatively angle independent and more suitable for tracking twist.
OBJECTIVE
This study was designed to test and compare the accuracy of tissue Doppler and 2D based strain measuring methods in tracking torsion.
METHODS
We constructed a twist model using a variable speed motor which was used to rotate a thin plastic rod. A continuous thin layer of beef was wrapped around this rod and it was placed in a water bath to ensure an optimal scanning window. The model was rotated at seven different speeds (20-80 cycles/min) and at two different degrees of twist (45° and 90°). Tension in the roll increased slightly during rotation. Short axis 2D and tissue Doppler images were acquired using a GE/VingMed Vivid 7 at 3.5 MHz and >100 frames/sec. Data was analyzed offline on EchoPac® for tissue Doppler based strain and a new 2D strain rate program embedded in EchoPac®. Tissue Doppler data was analyzed for computation of strain and strain rate at different points across the short axis view, and 2D images were analyzed for strain and degree of torsion at comparable points.
RESULTS
The 2D program tracked torsion well at 45° (mean determination = 49.4° ± 2.2°[SD]), while it underestimated the 90° twist computation (mean =
Tracking Tissue Torsion by Tissue Doppler Based Strain Rate Imaging and a New Speckle Tracking
2D Strain/Motion Anaylsis Program: An In Vitro Study
Muhammad Ashraf, Monica T. Young, Amariek J. Jensen, James Pemberton, David J. Sahn
Oregon Health & Science University, Portland, OR
68.6° ± 15.5°), more at the highest twist rates
(Figures 2 & 3).
Figure 2. 2D underestimation of twist at 90°
Figure 3. 2D measurement of twist at 45°