We introduce an automated method for myocardial performance index (MPI), also known as Tei index, which is one of the most substantial indicators in the early screening of heart defects. Since assessing fetal cardiac functions using MPI has become a routine and significant process, there have been explicit requirements to automate MPI measurements. Due to small heart sizes of fetuses, we focus on the automation of modified MPI (Mod-MPI) which uses a single Doppler gate. The proposed method detects four valve click signals in Doppler waveforms using four image features which are extracted by vertical projection of Doppler waveforms after several transformations. To evaluate performance, 88 of fetal examinations were collected from a commercial ultrasound machine, and two clinical experts measured the Mod-MPI both manually and automatically. Quantitative comparisons based on intra-class correlation coefficients (ICC) yield that intra-observer reproducibility is higher when performing the proposed method (ICC=0.951 and 0.932 for observer 1 and 2) comparing to those of manual measurements (ICC=0.868 and 0.857 for observer 1 and observer 2). Thus, our method (ICC=0.962) reveals superior inter-observer reproducibility than that of manual method (ICC=0.597). Although mean difference from observer 2 (−0.062) is over three times larger than that of observer 1 (−0.018) due to different experiences, both of mean differences are acceptable. In conclusion, the proposed MPI measurement method can improve intra- and inter-reproducibility while providing reliable results.
An ultrasound vector Doppler imaging is useful for detecting flow components normal to the ultrasound beam
direction. However, the conventional vector Doppler imaging method suffers from the bias of the time interval between
samples caused by the mismatch between transmit and receive directions during demodulation. In this paper, a new
directional demodulation method, in which demodulation is performed with a modified sample interval depending on the
receive beam steered angle to reduce the bias occurred in a conventional ultrasound vector Doppler imaging is presented.
To evaluate the performance of the proposed directional demodulation method, the pre-beamformed radio-frequency
(RF) data from in-vitro experiments were obtained using a commercial ultrasound system and a Doppler string phantom.
The true flow velocity of the phantom was 0.3 m/s. The center frequency of 5 MHz and the pulse repetition frequency of
4 kHz were used for the experiments. Also, a 32-element sub-aperture on a 128-element 7.2-MHz linear array probe
were used for emission and reception while changing the flow direction from -45 degrees to 0 degree by a step of 5
degrees. The proposed directional demodulation method successfully visualizes all flow directions. In addition, it lowers
a bias on flow estimation compared to the conventional method (i.e., 0.0255±0.0516 m/s vs. 0.0248±0.0469 m/s of error
of velocity, 2.4862±3.8911 degrees vs. 2.4857±3.5115 degrees of error of direction, respectively). These results indicate
that the proposed directional demodulation method can enhances the accuracy in flow estimation for vector Doppler