Figure 2.

Extraction of the Doppler spectrum pixel per pixel from the Ultrafast Doppler acquisition. At each pixel (x,y) we have access to the high pass filtered in-phase/quadrature-phase (IQ) complex signal s(x,y,t). s(x,y,t) rotates in the complex plane with a speed related to the blood flow speed. Over a short temporal window (80 points, 27 ms), the power spectral estimation by Fourier Transform can be calculated and used as a gray-scale coded column in a spectrogram, completed by sliding the window over the entire temporal sample s(x,y,t).