To reduce speckle is spectral Doppler imaging, any oversampling relative to the velocity scale is used to create different data sets for the location at a given time. The different data sets have at least partially independent noise. Spectra are estimated from the different data sets and the resulting spectra combined into a spectrum with less speckle. To improve signal-to-noise ratio, the samples acquired for a given velocity scale are band-limited into different narrower bands. The portion of the spectrum estimated for each narrow band has a higher signal-to-noise ratio than a spectrum estimated for the entire band. The parts of the spectrum estimated for the different narrow bands are stitched together to provide a spectrum for the entire band with greater signal-to-noise ratio. In another approach, the user may input a narrow band relative to the velocity scale so that the corresponding part of the spectrum is provided with greater signal-to-noise ratio. Similar approaches may be used for color or flow imaging.
