Imaging transducer do not only emit ultrasound but also hearable sound. This adds an additional source of noise to the maternal soundscape. Depending on the device and set-up used the sound emitted vary in amplitude and its spectral frequency content. The talk will present results for different scanning modes used in routine screening procedures and will discuss possible impacts on the fetus.
A phantom has been developed to simulate a pregnant femal torso being in the last trimester. In this period a fetus has developed demonstrably its hearing ability. The phantom consists of a femal pelvic bone and parts of the spine to include possible sound wave reflections. Within the pelvic an artificial fetal head was placed with a calibrated microphone within its ear. On the outside of the phantom the transducer was placed with the possibility to change its angle refered to the microphone/ear location. 2 different ultrasound equipment (Toshiba SSH-140A, GE Voluson E8) running in different imaging modes and different clinical set-ups have been measured.
The resulting exposition varies widely depending on the set-up. Maximum amplitudes upto 81 dB for Doppler modes have been measured while B-, 3D- and 4D-modes can reach 79 dB to 75 dB. During 3D and 4D scanning the microphone was hit only temporarily depending on the characteristic scanning courses. Additionally the frequency components and the angle dependency of the amplitudes have been evaluated.
With this new phantom it is possible to measure the amplitudes reaching the fetus during screening quantitatively and lead support for further possible impacts. Modern equipment is capable to emit very high amplitudes locally if the ear is directly within the path which is the case for 3D- and 4D-mode scanning. The user´s choice of mode and set-up is
influencing the final output amplitude directly and shall be tuned consciously following the ALARA principle.
