Strain rate imaging using two-dimensional speckle tracking

Strain rate images (SRI) of the beating heart have been proposed to identif y non-contracting regions of myocardium. Initial attempts used spatial deri vatives of tissue velocity (Doppler) signals. Here, an alternate method is proposed based on two-dimensional phase-sensitive speckle tracking applied to very high frame rate, real-time images. This processing can produce high resolution maps of the time derivative of the strain magnitude (i.e., squa re root of the strain intensity). Such images complement traditional tissue velocity images (TVI), providing a more complete description of cardiac me chanics. To test the proposed approach, SRI were both simulated and measure d on a thick-walled, cylindrical, tissue-equivalent phantom modeling cardia c deformations. Real-time ultrasound images were captured during periodic p hantom deformation, where the period was matched to the data capture rate o f a commercial scanner mimicking high frame rate imaging of the heart. Simu lation results show that SRI with spatial resolution between 1 and 2 mm are possible with an array system operating at 5 MHz. Moreover, these images a re virtually free of angle-dependent artifacts present in TVI and simple st rain rate maps derived from these images. Measured results clearly show tha t phantom regions of low deformation, which are difficult to identify on ti ssue velocity-derived SRI, are readily apparent with SRI generated from two -dimensional phase-sensitive speckle tracking.