METHODS AND APPARATUS FOR ULTRASOUND IMAGING

1 . A method for automatically controlling the gain from a Doppler signal processor during ultrasound imaging comprising:

inputting returned ultrasound signals;

demodulating the returned ultrasound signals;

wall-filtering the returned ultrasound signals producing Doppler flow signals;

performing spectral analysis on the Doppler flow signals producing a Doppler spectrum;

setting a high level signal threshold;

setting a low level signal threshold;

setting a noise floor level threshold;

detecting a peak Doppler spectrum level and a Doppler spectrum maximum noise floor from the Doppler flow signals;

increasing Doppler flow signal gain if the peak Doppler spectrum amplitude is less than the low level signal threshold until the peak Doppler spectrum amplitude equals the high level signal threshold or the maximum noise floor is equal to the noise floor level threshold; and

decreasing the Doppler flow signal gain if the peak Doppler spectrum amplitude is greater than the high level signal threshold until the peak Doppler spectrum amplitude equals the high level signal threshold or the maximum noise floor is equal to the noise floor level threshold.

2 . The method according to claim 1 further comprising smoothing the Doppler spectrum using a low-pass filter.

3 . The method according to claim 1 wherein the determination of whether the peak Doppler spectrum amplitude is greater than the high level signal threshold further comprises:

counting a number of consecutive Doppler spectrum frequency components whose amplitudes are greater than the high level signal threshold; and

comparing the number of consecutive Doppler spectrum frequency components whose amplitudes are greater than the high level signal threshold with a predetermined number, wherein if the number of consecutive frequency components is greater than the predetermined number, the peak Doppler spectrum amplitude is greater than the high level signal threshold.

4 . The method according to claim 1 wherein the determination of whether the peak Doppler spectrum is less than the low level signal threshold further comprises:

counting a number of consecutive Doppler spectrum frequency components whose amplitudes are greater than the low level signal threshold; and

comparing the number of consecutive Doppler spectrum frequency components whose amplitudes are greater than the low level signal threshold with a predetermined number, wherein if the number of consecutive frequency components is less than the predetermined number, the peak Doppler spectrum amplitude is less than the low level signal threshold.

5 . The method according to claim 1 wherein detecting the Doppler spectrum maximum noise floor further comprises:

calculating an average amplitude of a predetermined number of the consecutive Doppler spectrum frequency components, for all spectrum frequency components excluding frequency components near a zero frequency baseline;

determining a minimum average amplitude among the average amplitudes; and

determining the maximum noise floor as the minimum average amplitude multiplied by a predetermined factor.

6 . A system for automatically controlling the gain of a Doppler spectrum processor during ultrasound imaging comprising:

a receiver configured to receive returned ultrasound signals and having an output;

a Doppler signal processor having an input coupled to the receiver output and an output, the Doppler signal processor configured to demodulate and wall-filter the returned ultrasound signals and output Doppler flow signals;

a variable gain amplifier having an input coupled to the Doppler signal processor output, a gain control signal input and an output, the variable gain amplifier configured to vary the gain of the Doppler flow signals;

a spectrum analyzer having an input coupled to the variable gain amplifier output and an output, the spectrum analyzer configured to convert the Doppler flow signals into their corresponding frequency spectrum; and

an automatic gain engine coupled to the spectrum analyzer output, the automatic gain engine configured to receive the Doppler spectrum and detect a peak Doppler spectrum amplitude and a maximum noise floor wherein a gain control signal is calculated and coupled to the variable gain amplifier gain control signal input based on the maximum noise floor present in the Doppler flow signals spectrum and predetermined high, low and noise floor signal level thresholds wherein if the peak Doppler spectrum amplitude is greater than the high level signal threshold, or less than the low level signal threshold, overall gain is adjusted to maintain the peak Doppler spectrum amplitude greater than the low level signal threshold and less than the high level signal threshold.

7 . The system according to claim 6 wherein if the peak Doppler spectrum amplitude is less than the low level signal threshold, the automatic gain engine is further configured to increase the Doppler gain signal until the peak Doppler spectrum equals the high level signal threshold or the maximum noise floor is equal to the noise floor level threshold.

8 . The system according to claim 6 wherein if the peak Doppler spectrum amplitude is greater than the high level signal threshold, the automatic gain engine is further configured to decrease the Doppler gain signal until the peak Doppler spectrum amplitude equals the high level signal threshold or the maximum noise floor is equal to the noise floor level threshold.

9 . The system according to claim 6 wherein the automatic gain engine further comprises a low-pass filter configured to smooth the Doppler spectrum.

10 . The system according to claim 6 wherein the automatic gain engine is further configured to count a number of consecutive frequency components of the peak Doppler spectrum whose amplitudes are greater than the high level signal threshold and compare the number of consecutive frequency components whose amplitudes are greater than the high level signal threshold with a predetermined number, wherein if the number of consecutive frequency components is greater than the predetermined number, the peak Doppler spectrum amplitude is greater than the high level signal threshold.

11 . The system according to claim 6 wherein the automatic gain engine is further configured to count a number of consecutive frequency components of the peak Doppler spectrum whose amplitudes are greater than the low level signal threshold and compare the number of consecutive frequency components whose amplitudes are greater than the low level signal threshold with a predetermined number, wherein if the number of consecutive frequency components is less than the predetermined number, the peak Doppler spectrum amplitude is less than the low level signal threshold.

12 . The system according to claim 6 wherein the automatic gain engine is further configured to detect the Doppler spectrum maximum noise floor from an average amplitude of a predetermined number of the consecutive Doppler spectrum frequency components, for all spectrum frequency components excluding frequency components near a zero frequency baseline, and among the average amplitudes determines a minimum average amplitude wherein the maximum noise floor is the minimum average amplitude multiplied by a predetermined factor.

13 . A method for suppressing noise manifest on Doppler spectrum signals comprising:

inputting the Doppler spectrum signals;

receiving a Doppler gain control signal;

using a noise suppression gain curve g(p) corresponding to the Doppler gain control signal; and

processing the Doppler spectrum amplitudes with the noise suppression gain curve g(p) wherein each frequency of the Doppler spectrum amplitude is adjusted according to a response of the noise suppression gain curve.

14 . The method according to claim 13 wherein using a noise suppression gain curve further comprises generating a noise suppression curve g(p) corresponding to the Doppler gain control signal.

15 . The method according to claim 13 wherein using a noise suppression gain curve further comprises selecting a noise suppression curve g(p) corresponding to the Doppler gain control signal.

16 . A noise suppressor for suppressing noise manifest on Doppler spectrum signals comprising:

an input configured to receive gain adjusted Doppler spectrum signals;

a gain control signal input configured to receive a gain control signal that is used to adjust the gain for the gain adjusted Doppler spectrum signals to generate a noise suppression gain curve g(p);

a gain function processor configured to process the gain adjusted Doppler flow signals with the noise suppression gain curve g(p), wherein each spectrum component of the Doppler spectrum signal input is adjusted in amplitude according to the response of the noise suppression gain curve g(p); and

an output configured to output noise suppressed, gain adjusted Doppler flow signals.

17 . The noise suppressor according to claim 16 wherein the gain function processor further comprises a first look-up table containing a noise suppression gain curve g(p) which is received from a noise suppression curve generator which generates a noise suppression gain curves in response to the gain control signal.

18 . The noise suppressor according to claim 16 wherein the gain control signal selects one of the plurality of noise suppression gain curves g(p) having a predetermined response that corresponds to the gain control signal.

19 . The noise suppressor according to claim 16 wherein the gain function processor further comprises a calculator combined with a LUT which generates a noise suppression curve from a stored noise suppression and the gain suppression curve.

20 . The noise suppressor according to claim 16 wherein the gain function processor is selected from the group consisting of a calculator, a calculator and look-up table, or a plurality of look-up tables.

21 . The noise suppressor according to claim 17 wherein the suppression curve generator further comprises a calculator and a look-up table which includes a plurality of noise suppression gain curves.