The peak MEBR was calculated by replacing IE with IEP in Eq. (1) where IEP is the maximum intensity of backscatter from the embolus. The duration of the embolus was also extracted in milliseconds and the zero-crossing frequency (ZCF) in Hertz. The latter was then used to calculate embolus velocity via the Doppler equation. Velocities Selisistat are

angle-corrected based on a Doppler angle of 30°. Pearson correlation tests were then used to discern if any correlation exists between these properties. Eleven patients tested positive for a PFO yielding 331 embolic signals with intensities less than 35 dB. Table 1 displays the average values for various signal properties along with median values and 5% and 95% percentiles due to the non-normal distribution of these properties. 90% of gaseous emboli possess MEBR values between 7.9 and 21.7 dB and peak MEBR values between 17.4 and 31.3 dB. The majority of microbubble signals lasted between 12.3 and 91.6 ms

with a median signal duration of 33.3 ms. Combining the above information a characteristic peak for microbubble signals was observed with a peak at ∼15.6 dB and duration of ∼33.3 ms (see Fig. 1). The median ZCF of 520 Hz corresponds to an estimated velocity of 23.2 cm s−1 and 90% of the signals had velocities between approximately 10.9 and 45.6 cm s−1. Table 2 lists the Pearson correlation coefficients for various pairs of embolic signal parameters. Pearson correlation tests showed a weak positive Ibrutinib correlation between estimated velocity and duration (0.24, p < 0.0001). A weak negative correlation was also found for the average MEBR and embolic signal duration (−0.16, p < 0.01). The signal properties from 331 microbubbles have revealed some interesting distinguishing features that differ from the same signal properties previously analysed for solid emboli [11]. The majority of solid emboli in [11] had signal durations between 6.2 and 40.5 ms which are much shorter than the range observed for gaseous emboli in this study (12.3–91.6 ms). Astemizole Solid emboli had a distinctive peak at ∼7 dB with a duration of ∼12.5 ms which contrasts

with that observed for gaseous emboli (peak at ∼15.6 dB, duration ∼33.3 ms). This indicates that gaseous emboli tend to have higher MEBR values with longer durations compared to solid emboli. A weak negative correlation was observed between MEBR and embolic signal duration for microbubbles (−0.16, p < 0.01) compared to the positive correlation found for solid emboli (0.57, p < 0.0001). This positive correlation was also noted by Martin et al. who where studying the relationship between thrombus size and MEBR [12]. They found that larger solid emboli generated signals of longer duration. The weak negative correlation between MEBR and signal duration for microbubbles may relate to a preferred trajectory through the insonated vessel. The velocity distribution shown in Fig.