OP06.10: is Doppler Ultrasound Still Dangerous?

Education of ultrasound operators stresses that Doppler examination produces high-energies and should not be used in early pregnancy due to the risk of potential damage to the embryo. As new devices are getting better in imaging we investigated the maximum energy output. Temperature measurements were carried out in a specially developed test object containing 4 thermal sensors arranged in a line at different depths. In total we have tested 6 different probes (vaginal/obstetrics) from 3 systems. For each measurement we obtained the maximal thermal index (TI) and mechanical index (MI) of the specific probe-console combination using spectral and transcranial Doppler modes. The Doppler volume and focus were directed on the second sensor. The Doppler path was fitted on the line of the sensors. The surface temperature of the probe was also recorded. Data was acquired with 3 different TI/MI settings. Temperature increase depends on the special modes chosen (color (CD), Spectral (SD), combination) and is for spectral Doppler mode alone the highest. It also depends on the relative positions of the focus and sample volume. If both parameters coincide, maximum temperature increase could be measured. Above and below the target sensor changes were lower. The probe's surface shows the highest increase of temperature of up to 2.4 °C increase at 5 min of emission. The TI value is not a physical quantity and therefore can not be measured. A special tissue model is used to calculate TI values. Measured temperature rise and TI are not directly related. For the user of a system it is hard to estimate where the highest temperature increases could occur within the sound field. Additionally the increase varies from system settings and probe used. Therefore we believe that even with modern ultrasound devices Doppler examination should not be done routinely in early pregnancy as the temperature increase might have teratogenic effects.