where f0 is the frequency of the incident ultrasound beam, C is the velocity of sound in the tissue, and J is the incident angle of the ultrasound beam relative to the blood vessel of ventricle. In Doppler display mode, blood flowing toward the transducer is coded red; blood flow away from the transducer is shown as blue. Further, the intensity of the red or blue is displayed as proportional to the velocity. According to the foregoing equation, velocities are most accurate when the angle between the ultrasound beam and blood flow is close to 0, since the cosine of 0 is equal to 1. Pulsed wave ultrasound techniques may be used to assess blood velocity: a series of rapid pulses is sent into the tissue, followed by a short segment of time for receiving the reflected waves.
M-MODE DISPLAY M-mode display is unique in medical imaging to echocardiography. The primary advantage of this display mode is that high time resolution, to approximately one-thousandth of a second, can be displayed on the time axis. Compared with this, traditional 2d displays are updated only approximately 30 times per second. Thus, M-mode display has excellent time resolution and can be used to display the periodic motion of, for example, cardiac valves or vegetations. In this display mode, a 2D display is typically first selected. A single line, or slice, of the 2D display is then selected, often across a valve plane. M-mode displays then show the reflected ultrasound signal along this single line, with continual updating every millisecond.
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