202 Figure 8.1: 2D Transvaginal ultrasound image of uterus in midsagittal section. The region denoted by the blue and red markers is the junctional zone (JZ) where the uterine contraction features are observed and measured. The yellow arrows visualize movements in the longitudinal direction, and the green arrows illustrate movements in the radial direction. AW: Anterior Wall; PW: Posterior Wall. Contraction Frequency: Frequency features were analysed in the longitudinal and radial direction (see figure 8.1). Frequency-related features are reported as contractions per minute (221). Further technical details about feature extraction and analysis can be found in Sammali et al. (2019) (267). Contraction Amplitude: Contraction amplitude features reflect the relative strength of uterine contraction(221). Results are reported for contractions in the longitudinal direction. Contraction Direction Uterine contractions propagate in either the fundus-to-cervix (F2C) or the cervix-to-fundus (C2F) direction. The radial strain signal representation in the spatiotemporal frequency domain was analysed, where the spatial domain is intended along the longitudinal direction of the uterus (229). The ratio between the strain signal energy in the quadrants corresponding to the two propagation directions (C2F and F2C) provided a global measure of the dominant propagation direction in each wall (229). A more positive value
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