FETAL HEART MONITORING

• US 20110172540A1
• Filed: 09/16/2009
• Published: 07/14/2011
• Est. Priority Date: 09/23/2008
• Status: Active Grant

• Current Assignee: Huntleigh Technology, Inc.
• Original Assignee: Huntleigh Technology, Inc.
• Inventors: Jackson, Roy
• Granted Patent: US 8,579,820 B2
• Time in Patent Office: Days
• US Class Current: 600/453
• CPC Class Codes: A61B 8/02 Measuring pulse or heart rate
• CPC Class Codes: A61B 8/0866 involving foetal diagnosis; pre-natal or peri-natal diagnosis of the baby

Abstract

Fetal heart rate monitoring using ultrasound by means of a transducer in contact with the maternal abdomen. The transducer (11) is driven by a transmit amplifier (12), a receive amplifier (13) amplifies the echoes detected by the transducer. While the receive gate is open, demodulator (14) multiplies the received signal by the local oscillator signal. The sum of the frequencies is removed by low-pass filter (15), while the difference of the frequencies is the Doppler frequency of the received signal which passes through the filter to be digitised by ADC (16), the Rx gate opening a fixed delay after the end of the transmit pulse. A number of range bins are chosen and two ADC readings are made for each bin in intervals during the Rx gate-open interval. One or two of the Doppler audio signals, aperiodic or periodic, will contain the signal from the fetal heart. When a periodic signal is found, its rate is tested to see if it lies within or outside the typical range of a fetal heart.

Claims

1. A fetal heart monitoring system using ultrasound having a single receive circuit with a single, fixed, wide receive gate with the output being digitised repeatedly by an analogue to-digital converter (ADC) during the gate open interval with each digital value assigned to one of several range bins.

2. A fetal heart monitoring system as claimed in claim 1 wherein each range bin is arranged to accept a single ADC sample.

3. A fetal heart monitoring system as claimed in claim 2 wherein two or more ADC samples are assigned to each bin, the samples within each bin processed to produce a single signal within each bin.

4. A fetal heart monitoring system as claimed in claim 1 wherein a different gain is applied to each range bin.

5. A fetal heart monitoring system as claimed in claim 1 wherein the sensitivity individually in the range bins is adjusted by adjusting the threshold required for a signal to be detected or by applying different weightings to each range bin.

6. A fetal heart monitoring system as claimed in claim 1 wherein the range bins are recombined in pairs, trios, or groups of any number to recreate a composite signal corresponding to the depth range of those bins.

7. A fetal heart monitoring system as claimed in claim 6 wherein the range bins are recombined after applying an individual attenuation factor to each bin to simulate the use of a higher ultrasound frequency or create an arbitrary attenuation profile.

8. A fetal heart monitoring system as claimed in claim 1 wherein the amplitudes of the signals in all the range bins are compared to detect any sudden rise in amplitude across all the range bins showing the presence of an artefact caused by transducer movement.

9. A fetal heart monitoring system as claimed in claim 8 wherein the amplitude of the artefact is detected as a numerical value rather than a simple on/off indication.

10. A fetal heart monitoring system as claimed in claim 8 wherein the volume of the Doppler signal is modulated during the artefact.

11. A fetal heart monitoring system using ultrasound including:

(a) an ultrasound transducer configured to generate and receive acoustic signals;

(b) a transmit circuit configured to drive the ultrasound transducer by generating a transmit signal having a period;

(c) a receive circuit configured to receive signals from the ultrasound transducer during a single gate-open interval in each period; and

(d) an analogue-to-digital converter configured to digitise signals from the receive circuit, wherein the fetal heart monitoring system is configured to assign each digitised value to one of several range bins.

12. The system of claim 11 wherein the gate-open interval begins a fixed delay following generation of the transmit signal by the transmit circuit.

13. The system of claim 12 wherein:

(a) the gate-open interval includes a gate opening and a gate closing;

(b) the gate opening corresponds with a smallest depth within a maternal abdomen from which signals are received by the ultrasound transducer; and

(c) the gate closing corresponds with a largest depth within the maternal abdomen from which signals are received by the ultrasound transducer.

14. The system of claim 13

(a) wherein the fetal heart monitoring system is configured to assign two or more consecutively digitised values to each range bin;

(b) further including a processing unit configured to;

(i) process the two or more digitised values assigned to each range bin to produce a single signal for each range bin; and

(ii) combine the single signals of two or more range bins to generate a composite signal corresponding to a depth range within the maternal abdomen.

15. The system of claim 14 wherein:

(a) the transmit signal includes a transmit signal start and a transmit signal end; and

(b) the fetal heart monitoring is configured such that the gate-open interval lasts at least half the duration from the transmit signal end of a first transmit signal to the transmit signal start of a second transmit signal, the second transmit signal immediately following the first transmit signal.

16. A fetal heart monitoring system using ultrasound including a receive circuit configured to:

(a) receive signals from a transducer,

(i) the transducer being driven by a transmit circuit,

(ii) the transmit circuit generating a transmit signal having a period;

(b) amplify signals received from the transducer, the receive circuit having a single gate-open interval during which signals are received in each period, wherein the output of the receiver circuit is digitised by an analogue-to-digital converter to produce digitised values, with each digitised value assigned to one of several range bins.

17. The system of claim 16 wherein the gate-open interval of the receive circuit is timed to begin a fixed delay following the transmit signal.

18. The system of claim 16 wherein the gate-open interval of the receive circuit lasts at least half the duration of the period.

19. The system of claim 16 wherein the gate-open interval of the receive circuit includes a gate opening and a gate closing,

(a) the gate opening controlling a smallest depth within the maternal abdomen from which transducer signals are amplified,

(b) the gate closing controlling a largest depth within the maternal abdomen from which transducer signals are amplified by the receive circuit.

20. The system of claim 16 wherein the system is configured to combine two or more range bins after applying an attenuation factor to each range bin to simulate a higher ultrasound frequency.

21. The system of claim 16 wherein:

(a) two or more digitised values are assigned to each range bin, the digitised values in each range bin being processed to produce a single signal in each range bin;

(b) the single signal in each range bin corresponds to a depth within a maternal abdomen; and

(c) the single signals of two or more range bins are combined to create a composite signal corresponding to a depth range within the maternal abdomen.

22. The system of claim 21 wherein the system is configured to adjust the sensitivity of each range bin by applying a detection threshold for signals assigned to each range bin.

23. A method of using ultrasound to monitor a fetal heart including:

(a) driving a transducer using a transmit circuit, the transmit circuit generating a transmit signal having a period;

(b) receiving and amplifying signals received from the transducer using a receive circuit, the receive circuit having a single gate-open interval during which signals are received in each period;

(c) digitising the output of the receiver circuit using an analogue-to-digital converter to produce digitised values; and

(d) assigning each digitised value to one of several range bins.

24. The method of claim 23 wherein the gate-open interval of the receive circuit:

(a) is timed to begin a fixed delay following the transmit signal; and

(b) includes a gate opening and a gate closing,

(i) the gate opening controlling a smallest depth within a maternal abdomen from which transducer signals are amplified,

(ii) the gate closing controlling a largest depth within the maternal abdomen from which transducer signals are amplified by the receive circuit.

25. The method of claim 24 further including the steps of:

(a) assigning two or more digitised signals to each range bin;

(b) processing the digitised signals in each range bin to produce a single signal within each range bin, each signal corresponding to a depth within the maternal abdomen; and

(c) combining the single signals of range bins into groups of two or more range bins to generate composite signals corresponding to a range of depths within the maternal abdomen.