Fetal heart rate counting system using digital signal processing
First Claim
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1. A system for determining fetal heart rate data for use in a fetal monitor, comprising:
- means for transmitting a signal into the fetal heart while the fetus is in utero;
means for receiving a returning Doppler signal from the fetus, frequency-shifted by action of the fetal heart;
means for processing the returning Doppler signal so as to produce simultaneously a plurality of processed Doppler signals occupying a common band of frequencies, each processed Doppler signal representing a different component of the returning Doppler signal and containing fetal heart rate data;
means for obtaining fetal heart rate data from each of said processed Doppler signals; and
means for selectively combining the fetal heart rate data obtained from said processed Doppler signals in such a manner as to produce composite fetal heart rate data which is more accurate than the fetal heart rate data obtained from any of the processed Doppler signals individually.
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Abstract
A fetal heart rate counting system which includes a transducer element for transmitting an ultrasound signal into the fetal heart while the fetus is in utero and for receiving a returning Doppler signal frequency shifted by action of the fetal heart. The returning Doppler signal is processed to produce a forward heart movement Doppler signal, a reverse heart movement Doppler signal and the complete Doppler signal, from each of which fetal heart rate data is obtained. A composite fetal heart rate data is then produced from the three processed Doppler signal which is more accurate and complete than the data from any one signal individually.
21 Citations
25 Claims
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1. A system for determining fetal heart rate data for use in a fetal monitor, comprising:
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means for transmitting a signal into the fetal heart while the fetus is in utero; means for receiving a returning Doppler signal from the fetus, frequency-shifted by action of the fetal heart; means for processing the returning Doppler signal so as to produce simultaneously a plurality of processed Doppler signals occupying a common band of frequencies, each processed Doppler signal representing a different component of the returning Doppler signal and containing fetal heart rate data; means for obtaining fetal heart rate data from each of said processed Doppler signals; and means for selectively combining the fetal heart rate data obtained from said processed Doppler signals in such a manner as to produce composite fetal heart rate data which is more accurate than the fetal heart rate data obtained from any of the processed Doppler signals individually. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A system for determining optimum fetal heart rate data from a plurality thereof, comprising:
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means for obtaining a plurality of fetal heart rate data from a single returning Doppler signal, wherein each of the plurality of fetal heart rate data is the result of a different signal processing of the returning Doppler signal and thereby represents a different component of the returning Doppler signal; means for determining at successive points in time the validity of each of said plurality of fetal heart rate data; means for determining the signal quality of each fetal heart rate data at said successive points in time; and means selecting a valid one of said plurality of fetal heart rate data in accordance with preselected criteria at said successive points in time, including the signal quality of the valid fetal heart rate data. - View Dependent Claims (8, 9, 10, 11, 12, 13)
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14. A system for quadrature demodulation of a returning fetal heart rate Doppler signal which has been initially processed to produce a first Doppler signal and a second Doppler signal in quadrature relative to the first signal, comprising:
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means for adding the second Doppler signal to the first Doppler signal, producing a first processed Doppler signal; means for subtracting the first Doppler signal from the second Doppler signal, producing a second processed Doppler signal; means for providing the first Doppler signal unprocessed; and means rectifying the first processed Doppler signal to produce a first demodulated Doppler signal, rectifying the second processed Doppler signal to produce a second demodulated Doppler signal and rectifying the unprocessed first Doppler signal to produce a third demodulated Doppler signal, wherein the first demodulated Doppler signal represents fetal heart rate information corresponding to forward movement of the fetal heart valve and wherein said second demodulated Doppler signal represents fetal heart rate information corresponding to reverse movement of the fetal heart valve. - View Dependent Claims (15)
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16. A system for determining fetal heart rate from a demodulated Doppler signal returning from a fetus in utero, comprising:
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means for making a logarithmic compression of the demodulated Doppler signal; means for differentiating the log-compressed Doppler signal; means for detecting the zero crossings of the differentiated Doppler signal, wherein the zero crossings are indicative of a fetal heart beat; means for determining the number of fetal heart beats in a selected period of time from said zerocrossings to produce fetal heart rate data from said demodulated Doppler signal. - View Dependent Claims (17, 18, 19, 20, 21)
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22. A system for determining signal quality for a demodulated Doppler signal, comprising:
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means for determining fetal heart rate data from the demodulated Doppler signal; means for determining a signal to noise ratio estimate of the demodulated Doppler signal; means determining whether or not the signal to noise ratio estimate is above a pre-selected level, and for eliminating fetal heart rate data when the signal to noise ratio estimate is below said selected level thereby producing valid fetal heart rate data; means calculating the time between successive fetal heart beats in the valid fetal heart rate data; and means obtaining the average time difference value between successive fetal heart beats in the valid fetal heart rate data, said average time difference value being an indication of signal quality of the demodulated Doppler signal. - View Dependent Claims (23, 24, 25)
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Specification