Spectral doppler detection
In spectral pulsed wave Doppler imaging, spatial variance in signal and/or noise are reduced by combination of multiple spectra with at least partially decorrelated noise. Rather than requiring oversampling in time, the multiple spectra for one Doppler gate are created from different spatial signals. The Doppler gate is divided into sub-gates, the beamformed sample locations in the Doppler gate are grouped into two or more groups using any selection criterion, and/or different receive apertures are used to simultaneously sample the Doppler gate. Spectra for the gate are estimated from the samples with the different spatial content and then combined.
1. A method for spectral Doppler imaging, the method comprising:
acquiring, with an ultrasound system, first and second sets of samples representing response from a single spatial region for a range gate positioned at one location with a gate size, the first and second sets of samples having first and second spatial content, respectively, the first spatial content different than the second spatial content;
estimating, by a Doppler estimator, first and second spectra for the range gate from the samples of the first and second sets, respectively, the first and second spectra representing the response from the single spatial region at a same time;
combining the two or more spectra into a combined spectrum representing the response from the single spatial region at the same time; and
displaying a spectral Doppler strip with the combined spectrum representing the response from the single spatial region at the same time in the spectral Doppler strip.
2. The method of claim 1 wherein acquiring comprises transmitting with a pulse repetition frequency and acquiring samples for each of the sets in response to each repetition.
3. The method of claim 1 wherein acquiring comprises acquiring the first set of samples from a first sub-gate covering just a first part of the range gate and acquiring the second set of samples from a second sub-gate covering just a second part of the range gate, the first and second sub-gates defining the first and second spatial content.
4. The method of claim 3 wherein acquiring comprises acquiring with the first and second sub-gates overlapping but covering different ranges of depths within the range gate.
5. The method of claim 3 wherein acquiring comprises acquiring with the first and second sub-gates each comprising a set of contiguous beamform sample locations.
6. The method of claim 3 wherein acquiring comprises acquiring with the first and second sub-gates each comprising a set of dis-contiguous beamform sample locations.
7. The method of claim 1 wherein acquiring comprises forming the samples of the first and second sets with the first and second spatial content being responsive to transmits with reception using different receive apertures of a transducer array.
8. The method of claim 7 wherein forming comprises forming with the different receive apertures being overlapping on the transducer array.
9. The method of claim 1 wherein estimating comprises applying a Fourier transform to the samples of the first and second sets, the first and second spectra each comprising energy as a function of frequency over a range of the range gate.
10. The method of claim 1 wherein combining comprises summing the two or more spectra.
11. The method of claim 1 further comprising repeating the acquiring, estimating, and combining for different times, the different times for the repeating being other than the same time, and wherein displaying comprises displaying the spectral Doppler strip with each of the combined spectra representing the different times.