Strain rate measurements with ultra-high frame rate tissue Doppler imaging

Background: Strain rate imaging by tissue Doppler is vulnerable to noise, and has a low signal to noise ratio. To compensate for the low signal to noise ratio, temporal smoothing is required. A novel tissue Doppler acquisition method, Ultra-high Frame Rate Tissue Doppler Imaging (UFR-TDI), allows for a frame rate of 1200 frames per second (fps). This makes temporal smoothing feasible over far more samples than in conventional Tissue Doppler Imaging (TDI), which has a frame rate of 100-150 fps in a full sector view. In this study we examined whether a frame rate of 1200 fps would improve the repeatability of systolic strain rate measurements. Method: UFR-TDI was implemented on a Vivid E9 scanner with a M5S-D probe. Peak systolic strain rate was measured in ten young healthy male volunteers with both UFR-TDI and conventional TDI. Similar analysis settings were used in both acquisitions: Spatial averaging over a region of interest of 12mm*6mm, strain length 12mm and temporal smoothing (non Gaussian) over 30 ms. Peak systolic strain rate was measured twice in the same recording by both methods in the mid-septal and mid-lateral wall. Mean values and intra-method repeatability were compared. Results: Results are given in table 1. UFR-TDI showed a trend towards measurements of higher magnitude in the septum and lateral wall. There was also a trend towards better repeatability with UFR TDI in both the septum and lateral wall. However, the differences were not statistically significant (p>0.05). Discussion: UFR-TDI showed a trend towards improved repeatability and lower peak values in measuring peak systolic strain rate. This indicates that increased frame rates may better temporal smoothing and reduce the influence of random noise on strain rate measurements.