Which of the following is/are true regarding Doppler assessment?

a. Conventional Dopplers admit an ultrasonic beam in the frequency of 2–10 MHz

d. More information can be obtained by spectral analysis

Of all of the diagnostic methods used in the noninvasive lab, Doppler ultrasound has the most utility. In clinical usage Doppler instruments emits an ultrasonic beam at 2–10 MHz. The frequency of the sound is changed in proportion to the velocity of moving particles (red blood cells) and the cosign of the angle of insonnation that the beam makes with the velocity vector. The frequency shift is in the audible range and listening with a pocket Doppler provides a quick and simple method of assessing blood flow. Spectral analysis with frequency on the vertical axis, time on the horizontal axis and amplitude changes indicated by an increasing intensity on the grey scale provides considerably more information, particularly with respect to flow disturbance which produce a broadening of the normally narrow bands of frequencies which parallel the flow envelope.