A comparison of colour flow imaging algorithms.

In this paper we will present and explain coherently the two main algorithms which are currently used in commercial colour flow imaging systems, namely the frequency domain based autocorrelation algorithm and the time domain based cross correlation algorithm. The autocorrelation algorithm is a robust optimum mean frequency baseband estimator, for both high and low signal to noise ratio (SNR). Its main disadvantage is its aliasing problem. However the cross correlation algorithm does not suffer from this problem, and this has been one of the main reasons for its development. The mathematics behind these two algorithms and the general data processing steps used for their implementation will be also presented. The subject of clutter removal filtering will be discussed and valuable points will be made. A practical relevant approach on how to discriminate between wanted blood flow related estimates and unwanted false estimates due to noise will be presented. On the aliasing problem of the autocorrelation algorithm, a promising solution known as spatial tracking of estimated mean frequency does exist, which will be also introduced in detail. Towards the end of this paper other algorithms, which are currently the subject of research and have potential for development, will be discussed.

A transducer for detecting foetal breathing movements using PVDF film.

Foetal breathing movement (FBM) in utero has come to play an important role in foetal diagnosis. FBM may be monitored using real time ultrasound imaging of the foetus in utero. Foetal breathing activities can also be detected by monitoring maternal abdominal wall movement in the frequency range of 0.5-2.5 Hz. This paper presents a transducer which detects FBM non-invasively by monitoring maternal abdominal wall movements. Foetal heart sounds can also be monitored. The transducer presented uses piezo-electric film as the transducing medium. Results from preliminary clinical trials of prototype transducers on 10 patients are discussed.

Linear time series analysis of long term fetal heart rate variability patterns.

Long term fetal heart rate variability (LFHRV) is equivalent to detrended (when the time series trend removed) indirectly derived averaged fetal heart rate (FHR) time series. Up to now LFHRV is looked for visually in FHR traces, by obstetricians and midwifes for determination of fetal condition. The detrended averaged FHR data or LFHRV data is a random correlated non-stationary (in second moment) time series. In this paper we have applied linear stochastic time series analysis technique to identify a parsimonious stochastic model, for parametric numerical representation of the random cyclical patterns observed in short 2 minutes quasi-stationary contiguous blocks of LFHRV data. The parametric estimation technique used is based upon the optimum exact Maximum likelihood estimation (which uses Kalman filtering as part of its implementation). Diagnostics performed on the residuals indicated that a second order autoregressive model is a statistically adequate model in capturing variability patterns observed in 2 minute data windows of detrended average FHR. Also through further analysis of the spectral behavior of this identified model, pseudo-periodicity (or random periodicity) which for a long time was visually detected, can now be detected via this numerical procedure.

A comparative clinical study of fetal phono- and movement-sensors from Amsterdam, Cambridge and Edinburgh.

In a European collaboration, a joint project to conduct an experimental and clinical investigation of recently developed sensors from three centres (Amsterdam, Cambridge and Edinburgh) has been carried out. The Amsterdam sensor was based on an inductive principle whereas the Cambridge and Edinburgh transducers used a piezo-electric material (PVDF) as transducing element. Nine patients with varying gestational age (29-38 weeks) were measured in a clinical investigation. Recordings of fetal heart sounds (FHS) and fetal breathing movements (FBM) were made using three sensors; one from each centre. These recordings were digitized directly into a computer using a purpose-built data acquisition system. For each patient 3 min of FBM data, and 1 min of FHS data were recorded by each sensor. The FBM recordings were carried out simultaneously with ultrasound, so as to enable a correlation to be made between both recordings. The FHS recordings were carried out simultaneously with the maternal heart pulse, to discount any maternal heart influences on the resulting signals. Of the nine patients analysed, FHS were recorded in seven patients. On the other hand, it appeared difficult to identify fetal breathing movements in the FBM recordings due to the dominance of the maternal breathing component. The analysis of the FBM signals and its correlation with ultrasound could not be carried out due to the relatively poor quality of the signals detected by the sensors, given the present techniques of analysis. The evaluation of the FHS recordings showed that although there is relatively little difference between the sensors, the inductive sensor performed best.

A comparative experimental study of fetal phono- and movement-sensors from Amsterdam, Cambridge and Edinburgh.

This paper describes the experimental studies and results of a collaborative investigation between three European institutes: Amsterdam, Cambridge and Edinburgh. The object of this investigation and the collaborative exchanges was to evaluate and compare different sensors for recording fetal sounds and movements from each centre. This would be carried out in a series of experimental and clinical tests involving researchers from each of the European institutes, and using three sensors: one from each centre. Experimental measurements have been performed regarding the conversion gain, frequency response, equivalent input noise and dynamic range of the transducers. The measurements were carried out using a vibration-free table testing rig to evaluate these characteristics of each of the sensors. The equivalent input noise ranged from 50 nm to 1600 nm for the transducers studied.

Autoregressive spectral estimation of fetal breathing movement.

Fetal breathing movement (FBM) in utero may be an indicator of fetal health. This paper provides a second-by-second estimate of FBM rate. In the absence of a statistical model for the fetal breathing movement, block data structured autoregressive spectral estimation is used. The optimum tapered Burg algorithm provides a minimum variance breathing rate estimate from a short block of data. The data were recorded using a PVDF (PolyVinyliDeneFluoride) transducer which picks up maternal abdominal wall movements. A peak tracking algorithm is used to extract the fetal breathing rate. Results from these signals are presented in graphical form. Further analysis of the fetal breathing rate has revealed periodicities, similar to that observed in the fetal heart rate.

Real time processing and analysis of fetal phonocardiographic signals.

The monitoring of fetal heart rate (FHR) is commonly used in assessing the general health of the fetus. Although certain periodic cycles may be indicative of fetal problems, only short term observations are routinely employed in clinical practice. This is due to cost considerations, inconvenience to the patient and concern about long term ultrasonic monitoring. Therefore only a low confidence assessment can be established between detected rhythms and the health of the fetus. The technique advocated in this paper makes use of an inexpensive, non-invasive phonocardiographic (phono) transducer which facilitates safe long-term patient monitoring. A variable comb filter applied to the frequency domain is used in order to take full advantage of the harmonic content of fetal heart signals. Real time estimation of FHR has been achieved on pre-recorded phono signals lasting eight hours. Recordings with a reasonable signal quality were analysed and some of the results are given. Advanced signal processing techniques followed by Artificial Intelligence (AI) algorithms reduce the number of erroneous estimates during periods of low signal to noise ration (SNR). The resulting FHR time series is stored on the host computer for further processing, display and parameter extraction. This paper outlines the processing steps involved.

Computerized home telemetry of maternal blood pressure in hypertensive pregnancy.

We have developed a telemetric technique whereby maternal blood pressure, which is self-measured by pregnant women in their own homes using a Dinamap 1846 automated blood pressure recorder, can then be transmitted over the commercial telephone network into the Rosie Maternity Hospital in Cambridge, where it is computer-processed. The maternal blood pressure is then reviewed by the obstetrician as part of the clinical management protocol. We have used this telemetric technique on 90 occasions, from the homes of 10 pregnant hypertensive women. On almost every occasion, the blood pressure measured at home was lower than that previously measured in the hospital antenatal clinic. This technique offers great promise, both in terms of health economics and also in terms of reducing pregnant women's unhappiness about their being admitted to hospital whenever they exhibit moderate to severe hypertension in the antenatal clinic. Indeed, in the antenatal period, home telemetry should allow the vast majority of hypertensive pregnancies to be managed just as safely at home as in hospital. In the management of high risk pregnancy, home telemetry of maternal blood pressure complements three other home telemetric techniques which have already been described: fetal heart rate, maternal blood glucose and uterine contractions.

A signal-processing research facility and its application to the processing of fetal phonocardiographic signals for heart rate estimation.

Part 1 of this paper describes a real-time medical signal-processing research facility which is being developed at Edinburgh University. Part 2 describes the application of this facility to the estimation of fetal heart rate from phonocardiographic signals using a new frequency-domain estimation algorithm.

CEUSPEC--a computerized system for fetal home telemetry.

We have developed a computerized system whereby the fetal heart rate can be recorded telemetrically from patients' homes, transmitted over conventional public telephone lines, and then computer-processed in real time in the obstetric unit.