Improved recognition of dysfunctioning myocardial segments by longitudinal strain rate versus velocity in patients with myocardial infarction.

Doppler tissue imaging (DTI) can measure myocardial velocities but velocities alone cannot distinguish active from passive wall motion, whereas this is possible by strain rate (SR) imaging (SRI). We evaluated the accuracy of SRI for recognition of abnormal regional systolic function compared with DTI, B-mode echocardiography, and anatomic M-mode in 24 patients with myocardial infarction who underwent gated stress Tc 99m sestamibi scan. Sensitivity and specificity for recognition of infarct segments were 91% and 84% for visual SRI, 63% and 73% for visual DTI, 78% and 71% for B-mode echocardiography, and 87% and 77% for anatomic M-mode, respectively. Peak SRs correlated with wall-motion assessment by B-mode echocardiography better than peak velocities (P =.66 vs.10), with less overlap between groups. Therefore, SRI improves evaluation of regional wall motion compared with DTI and conventional ultrasound techniques in patients with myocardial infarction, mainly because it identifies segments that are moving passively but not shortening normally.

In vitro evaluation of ultrasound Doppler strain rate imaging: modification for measurement in a slowly moving tissue phantom.

Doppler strain rate imaging (SRI) was evaluated in vitro using a silicone strip phantom mimicking slowly moving tissue. A test apparatus was developed that enabled controlled strain experiments with variable strain and strain rate to be performed. SRI strain was measured at eight different calculated strains (range 5.7 to 63.4 %) at three different pump speeds with tissue velocity 0.1, 0.5 and 1.0 mm/s. The effect of varying tissue velocity and strain sample size on the measured SRI strain was elaborated. SRI strains agreed well with calculated values for strain when SRI strain was measured as the average over the whole strip cross-section and the strain sample size was 1.9 mm (mean difference = 2.78%, limits of agreement +/- 9.97% for tissue velocity 1.0 mm/s, n = 8). The variance was substantial if single central samples were used, especially for strain sample size of 0.8 mm (mean difference = -7.47%, limits of agreement +/- 20.90 for tissue velocity 0.5 mm/s, n = 24). Increasing the strain sample size to 1.9 mm removed some of the underestimation (giving mean difference of -4.46%, n = 24). We found low intra- and interobserver variation. This study indicates that, for the SRI method to give accurate estimates of strain, strain sample size should be in the region of 2 mm. Averaging over several ultrasound (US) beams increased the accuracy further.

Strain during gastric contractions can be measured using Doppler ultrasonography.

This study was undertaken to explore if strain of the muscle layers within the gastric wall could be measured by transabdominal strain rate imaging (SRI), a novel Doppler ultrasound (US) method. A total of 9 healthy fasting subjects (8 women, 1 man; ages 22 to 55 years) were studied and both grey-scale and Doppler US data were acquired with a 5- to 8-MHz linear transducer in cineloops of 97 to 256 frames. Rapid stepwise inflation (5 to 60 mL) of an intragastric bag was carried out and bag pressure and SRI were measured simultaneously. SRI enabled detailed studies of layers within the gastric wall in all subjects. Great variations in strain distribution of the muscle layers were found. Radial strain was much higher in the circular than in the longitudinal muscle layer. Strains derived from SRI correlated well with strains obtained with B-mode measurements (r = 0.98, p < 0.05). During balloon distension, we found an inverse correlation between pressure and radial strain (r = -0.87, p < 0.05). Intraobserver correlation of strain estimation was r = 0.98 (p < 0.05) and intraobserver agreement was 0.2% +/- 18.6% (mean difference +/- 2SD, % strain). Interobserver correlation was r = 0.84 (p < 0.05) and interobserver agreement was 6.9% +/- 56.8%. SRI enables detailed mapping of radial strain distribution of the gastric wall and correlates well with B-mode measurements and pressure increments.

Strain Rate Imaging by Ultrasound in the Diagnosis of Regional Dysfunction of the Left Ventricle.

BACKGROUND: Regional strain rate in the left ventricle can be assessed by tissue Doppler velocity gradient and color mapped in real time. Regional contractility thus can be visualized and graded. To validate the method, we made a comparison with standard echocardiography. METHODS AND RESULTS: Fifteen patients with recent myocardial infarction were examined with the use of strain rate imaging (SRI). Velocity gradients were mapped by color. Gray-scale imaging was performed using the second harmonic mode. Cine loops of two-dimensional echocardiography (2-D echo) and SRI images from three standard apical planes were analyzed off line. A four-grade scale in 16 segments was used to score wall motion by 2-D echo and by SRI. Of a total of 236 segments, 235 segments were analyzable by 2-D echo and 218 segments were analyzable by SRI. Correlation of wall motion score index with ejection fraction was - 0.84 by 2-D echo and - 0.92 by SRI. One hundred fourteen segments had an equal score by the two methods: 51 segments differed by 1 degree and 14 segments differed by 2 degrees (kappa = 0.45). CONCLUSIONS: SRI agrees well with echocardiography in grading regional wall function, and the method can be seen as validated in a clinical setting for assessment of regional systolic wall function and is demonstrated to be applicable for semiquantitative wall motion assessment. SRI has theoretical advantages and may be a valuable addition to standard echocardiography, especially in the field of stress echocardiography.

Two-dimensional ultrasonic strain rate measurement of the human heart in vivo.

A study is presented in which the feasibility of two-dimensional strain rate estimation of the human heart in vivo has been demonstrated. To do this, ultrasonic B-mode data were captured at a high temporal resolution of 3.8 ms and processed off-line. The motion of the RF signal patterns within the two-dimensional sector image was tracked and used as the basis for strain rate estimation. Both axial and lateral motion and strain rate estimates showed a good agreement with the results obtained by more established, one-dimensional techniques.

Radial strain gradient across the normal myocardial wall in open-chest pigs measured with doppler strain rate imaging.

BACKGROUND: One of the reasons for the large variation in radial strain measured with Doppler strain rate imaging in normal myocardium might be the different strain length (SL) used during analyses. The aim of this study was to evaluate the effect of different SL settings on strain recordings and the method's ability to detect transmural radial strain gradients. METHODS: In 8 anesthetized pigs (mean weight 54 kg) epicardial echocardiography was performed. Strain analysis was carried out by defining the wall as a 1-, 2-, 3-, and 4-layer structure with suitable regions of interest. Peak ejection strain was measured with SL settings of 2 to 14 mm. RESULTS: The systolic (ejection) strain showed large variation with SL. Sampling in one layer gave no significant reduction in strain for increasing SL. The strain in the subepicardial layer was low and decreased when the wall was divided into several layers (15.9 +/- 4.8% [2 layers]-2.1 +/- 2.4% [4 layers]; both measurements with SL = 4 mm). The method could separate 4 layers with SL of 4 mm or less, 3 layers with SL of 6 mm or less, and 2 layers with SL of 8 mm or less. CONCLUSION: When measuring radial strain in the myocardial wall the SL must be low to evaluate transmural strain gradients. With correct settings of SL and region of interest, strain in 4 layers can be distinguished. As a rule of thumb the SL should be set to approximately half the systolic thickness of the wall or half the wall layer.