Ultrasound transducer positioning aid for fetal heart rate monitoring

Abstract

Abstract-Fetal heart rate (fHR) monitoring is usually performed by Doppler ultrasound (US) techniques. For reliable fHR measurements it is required that the fetal heart is located within the US beam. In clinical practice, clinicians palpate the maternal abdomen to identify the fetal presentation and then the US transducer is fixated on the maternal abdomen where the best fHR signal can be obtained. Finding the optimal transducer position is done by listening to the strength of the Doppler audio output and relying on a signal quality indicator of the cardiotocographic (CTG) measurement system. Due to displacement of the US transducer or displacement of the fetal heart out of the US beam, the fHR signal may be lost. Therefore, it is often necessary that the obstetrician repeats the tedious procedure of US transducer positioning to avoid long periods of fHR signal loss. An intuitive US transducer positioning aid would be highly desirable to increase the work flow for the clinical staff. In this paper, the possibility to determine the fetal heart location with respect to the transducer by exploiting the received signal power in the transducer elements is shown. A commercially available US transducer used for fHR monitoring is connected to an US open platform, which allows individual driving of the elements and raw US data acquisition. Based on the power of the received Doppler signals in the transducer elements, the fetal heart location can be estimated. A beating fetal heart setup was designed and realized for validation. The experimental results show the feasibility of estimating the fetal heart location with the proposed method. This can be used to support clinicians in finding the optimal transducer position for fHR monitoring more easily.

Fetal Heart Rate Monitoring Implemented by Dynamic Adaptation of Transmission Power of a Flexible Ultrasound Transducer Array

“…Due to reciprocity, the same characterization applies to the US beam in receive mode. Using experiments and simulations, it was shown that transmission with multiple elements, positioned in a rigid gird, leads to an US beam profile with multiple side lobes and interferences [ 20 , 28 ]. It should be noted that a group of seven concentrically arranged transducer elements (e.g., elements with index i = 1, i = 3, i = 4, i = 6, i = 8 and i = 9 in Figure 1 b), corresponds to the array aperture of a commercially available US transducer [ 20 , 28 ].…”

Doppler Ultrasound Technology for Fetal Heart Rate Monitoring: A Review

“…Such transducer geometry is shown in Fig. 5(a), for which the corresponding generated US pressure field was generated The US waves transmitted by such US transducers interfere, leading to local variations in the US pressure within the medium [77]. The local pressure variations affect the amplitude of the reflected US echo, which is eventually received by the array.…”

“…This may be a tedious task and requires experienced clinicians. To support clinicians in positioning the US transducer, methods have been developed to estimate the fetal location [61], [62], [77]. These methods exploit a multi-element array and measure the Doppler power in each individual transducer element, which is then put into a probabilistic framework for fHL estimation.…”

“…2(c). Commercially available fHR monitor typically use the envelope of the nondirectional Doppler signal, while other algorithms are based on the envelope of the directional Doppler signal [63], [77].…”

“…For more realistic measurements, in [61] and [62], an experimental setup was designed, in which a chicken heart is brought into a beat-like motion pattern within a water tank. US attenuation due to fat was obtained by adding an acoustic absorbing layer between the target and the US transducer, and this setup allows mimicking the out-of-beam motion of the heart due to FM or transducer displacement [77]. A limitation of the described setups is that no real heart contraction can be mimicked, disregarding the complex sequence of events during a cardiac cycle [see Fig.…”