Abstract
The aim of our study was to evaluate the thermal index (TI) and mechanical index (MI), during the assessment of the fetal heart at the time of first-trimester scan, with different ultrasound machines. This was part of an observational study conducted in patients undergoing routine first-trimester screening. Cases were examined with Voluson E8 or 730Pro scanners using 2–8 MHz transabdominal probes. TI and MI were retrieved from the saved displays while in gray mode, color flow mapping and pulsed-wave (PW) Doppler examinations of the fetal heart and also from the ductus venosus (DV) assessment. We evaluated 552 fetal cardiac examinations, 303 (55%) performed with Voluson E8 and 249 (45%) with Voluson 730Pro ultrasound machines. The gray-scale exam of the heart and the PW Doppler DV assessment had TI values significantly lower for the Voluson E8 group (median, 0.04 vs. 0.2 and 0.1 vs. 0.2, respectively). The MI values from gray-scale and color flow mapping of the heart were significantly lower (median, 0.6 vs, 1.2 and 0.7 vs. 1) and for PW Doppler exam of the tricuspid flow were significantly higher (median 0.4 vs. 0.2) in the Voluson E8 group. The TI values from Doppler examinations of the heart, either color flow or PW imaging and MI values from DV assessment were not significantly different between the two groups. A different (newer) generation of ultrasound equipment provides lower or at least the same safety indices for most of the first-trimester heart examinations.
Highlights
There is an increased interest in evaluation of the fetal heart while in the first trimester of pregnancy
Even if a detailed examination is impossible, a basic assessment of the fetal heart at 11 to 14 weeks of gestation has been investigated by some groups. [1, 2] there are several series reporting the detection of major cardiac defects.[3, 4]
We found that Voluson E8 machine does not show, by design,[15] the thermal indices (TIs) from gray-scale examinations of the heart with values below 0.04 and display them as 0.0
Summary
There is an increased interest in evaluation of the fetal heart while in the first trimester of pregnancy. Safety Indices on Fetal Echocardiography at First Trimester Scan demonstrating flow direction. There are often associated the tricuspid flow and ductus venosus (DV) pulsed-wave (PW) Doppler evaluation as a part of aneuploidy screening [5], improving the early detection of heart defects.[6]. Ultrasound machines have to display the thermal index (TI) and mechanical index (MI) on the screen during examination, as an indication of the likelihood of ultrasound-induced bioeffects. They encourage the end-user to become aware of safety issues and enable the application of ALARA (as low as reasonably achievable) principle. The MI indicates the potential for the ultrasound to induce cavitation. Because of the absence of a gas-liquid interface in the utero, this effect has not been documented in mammalian fetuses and there is no direct evidence to date as to whether or not this effect can occur in humans.[7]
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