Hee-chul Yoon

Automated measurement of fetal myocardial performance index in ultrasound Doppler waveforms

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.

Ultrasound semi-automated measurement of fetal nuchal translucency thickness based on principal direction estimation

The objective of the paper is to introduce a novel method for nuchal translucency (NT) boundary detection and thickness measurement, which is one of the most significant markers in the early screening of chromosomal defects, namely Down syndrome. To improve the reliability and reproducibility of NT measurements, several automated methods have been introduced. However, the performance of their methods degrades when NT borders are tilted due to varying fetal movements. Therefore, we propose a principal direction estimation based NT measurement method to provide reliable and consistent performance regardless of both fetal positions and NT directions. At first, Radon Transform and cost function are used to estimate the principal direction of NT borders. Then, on the estimated angle bin, i.e., the main direction of NT, gradient based features are employed to find initial NT lines which are beginning points of the active contour fitting method to find real NT borders. Finally, the maximum thickness is measured from distances between the upper and lower border of NT by searching along to the orthogonal lines of main NT direction. To evaluate the performance, 89 of in vivo fetal images were collected and the ground-truth database was measured by clinical experts. Quantitative results using intraclass correlation coefficients and difference analysis verify that the proposed method can improve the reliability and reproducibility in the measurement of maximum NT thickness.

Multi-scale synthetic filtering method for ultrasonic image enhancement

In this paper, a novel ultrasonic image enhancement method, i.e., multi-scale synthetic filtering (MSF) method is proposed for effectively suppressing speckle noise and enhancing structured region. The proposed MSF method is composed of the modified nonlinear coherence diffusion (NCD) model and the adaptive directional filter (ADF) both applied in multi-scale domain. Due to the difference in frequency characteristics of speckle and edge, Laplacian pyramid is adopted to analyze ultrasonic images. On each Laplacian sub-band, the modified NCD is performed to suppress speckle noise while preserving anatomical edges. Then, the ADF is applied to each synthesized images to sharpen and enhance detailed boundaries. The performance of the proposed MSF method is compared with the speckle reducing anisotropic diffusion (SRAD). For quantitative analysis, the contrast-to-noise ratio (CNR) values were computed on in vivo carotid artery ultrasound images. When compared with the SRAD, the average CNR gain of the proposed MSF method was 0.42 dB. The average processing time of the proposed method is 8.1 ms per one frame. The clinical evaluations and short running time indicate that the proposed MSF method can improve the diagnostic confidence in medical ultrasound imaging.