A new method describing cross-sectional blood flow velocity profiles in the left ventricular outflow tract of patients with atrial fibrillation with the use of high-frame rate 2-dimensional color flow imaging.

A new Doppler method was developed to evaluate the instantaneous cross-sectional velocity profile variability in the left ventricular outlet tract in patients with atrial fibrillation. Blood flow velocities acquired at a high frame rate (>90 frames/s) from a single heart cycle were used to display the velocity profile. In 9 patients, 2 heart cycles with different R-R interval lengths were recorded in color flow mode in a transthoracic apical 5-chamber and long-axis view. Raw digital ultrasound data were analyzed with an external personal computer. The data indicated a variable skew in the profiles with the highest velocities and velocity-time integral (VTI) most often located in the center and toward the septum. The maximum VTI overestimated the mean VTI by approximately 40%. No significant difference existed between the two heartbeats. Thus the VTI can be averaged from heartbeats of different R-R lengths in atrial fibrillation.

Statistical evaluation of clutter filters in color flow imaging.

The filter used to separate blood signals from the tissue clutter signal is an important part of a color flow system. In this paper, statistical detection theory is used to evaluate the quality of the most commonly used clutter filters. The probability of falsely classifying a sample volume as containing blood is kept below a specified threshold. With this constraint, the probability of correctly detecting blood is calculated for all the filters. Using a measured clutter signal, we found that polynomial regression filters and projection-initialized IIR filters are best among the commonly used filters. The probability of correctly detecting blood with velocity 10.1 cm/s was 0.32 for both these filters. The corresponding value for the optimal detector was 0.81, whereas a regression filter that depends on the clutter signal statistics achieved a blood detection probability of 0.72.

High frame rate strain rate imaging of the interventricular septum in healthy subjects.

OBJECTIVE: In the present study the feasibility was assessed of a new strain rate imaging method with a very high frame rate of around 300 frames per second. METHODS: Digital radio-frequency (RF) data were obtained in nine healthy subjects using a sector of 20-30 degrees in an apical four chamber view. The RF data were analysed using a dedicated software package that displays strain rate images and profiles and calculates strain rate values. With the new method, it is possible to study events and spatial-temporal differences in the heart cycle with duration down to 3.5-3 ms, including the pre-ejection period and the isovolumic relaxation period. Since the interventricular septum (IVS) is of crucial importance for the left and right ventricular function, we assessed changes through the heart cycle of the strain rate in the IVS. RESULTS: Mean peak systolic strain rate in the healthy subjects was -1.65+/-0.13 s(-1). Mean peak diastolic strain rate during early filling was 3.14+/-0.50 s(-1) and during atrial systole 0.99+/-0.09 s(-1). We found individual differences in the strain rate patterns, but in all subjects, the ventricular contraction started simultaneously in all parts of the septum. After the ejection period, the elongation started before aortic valve closure, in the midinferior septum and propagated towards the apex. CONCLUSION: High frame rate strain rate imaging makes it possible to study rapid deformation patterns in the heart walls.