Frame rate up-conversion in cardiac ultrasound

Abstract

The temporal resolution of echocardiographic sequences affects the interpretation of cardiac motion as well as the viewing experience. Temporal resolution, however, is limited by the propagation velocity of sound in tissue. Altering the acquisition system can improve temporal resolution but normally reduces image quality. Alternatively, motion compensated frame interpolation enhances perceived temporal resolution without reducing spatial resolution. There are however significant challenges with these techniques due to the simultaneous presence of large and small motions of the cardiac structures. In this paper, we propose a new motion compensated frame interpolation algorithm based on a variational bidirectional motion estimation model. We derive the Euler-Lagrange equations characterizing the optimal dense bidirectional motion field and develop a multiscale iterative procedure to obtain the motion field and the missing intermediate frames. The performance of the proposed algorithm was evaluated on real cardiac ultrasound recordings, using both subjective and objective evaluation criteria. Experimental results show that the interpolated frames generated by the proposed algorithm do not have the ghosting or blurring artifacts that are commonly present in the existing motion compensated frame interpolation algorithms, especially near fast moving structures like the cardiac valves. Quantitatively, the proposed algorithm achieves an improvement in the average peak signal-to-noise ratio of 1.16 dB and in the structural similarity index of 3.0%.