Comparison of regional myocardial velocities assessed by quantitative 2-dimensional and M-mode color Doppler tissue imaging: influence of the signal-to-noise ratio of color Doppler myocardial images on velocity estimators of the Doppler tissue imaging system.

M-mode color Doppler imaging of the myocardium affords a greater sampling rate and signal-to-noise (S/N) ratio than 2-dimensional (2D) imaging. In this study, we compared myocardial velocities assessed by 2D and M-mode Doppler tissue imaging (DTI) at the same site and evaluated the influence of the S/N ratio on velocity estimates of the currently used DTI systems. In patients with and without impaired regional left ventricular function, myocardial velocities assessed by 2D DTI were lower than those obtained with M-mode DTI. The difference between regional velocities derived from both imaging techniques was positively correlated with the extent of the "black zone," which could be considered as indirectly reflecting the S/N ratio for each frame. Thus in the clinical setting and on currently used echocardiographs, 2D DTI may provide underestimated regional myocardial velocities when compared with M-mode, mainly because of the influence of the lower sampling rate and S/N ratio on velocity estimators of the imaging system.