154 patient inclusion. Overall, 70 out of 96 conducted recordings from 64 women were included in the analysis. Data sources and measurements: TVUS measurement: Transvaginal ultrasounds (TVUS) were performed during several phases of the menstrual cycle: the menstrual phase (M, cycle day (CD) 1-5), mid-follicular (MF, CD 6-10), late follicular phase (LF, CD 11-14), early luteal phase (EL, CD 15-20) and late luteal phase (LL, CD 21-28). During each session, four-minute video recordings of the uterus in the mid-sagittal section were made. The employed ultrasound machines were an Accuvix WA80S with Elite (Samsung Medison, Seoul, Korea) equipped with a V5-9 transvaginal probe (bandwidth 5-9 MHz) or a GE Voluson S10 Expert (GE Healthcare, Zipf, Austria) equipped with a RIC5-9W-RS probe (bandwidth 3.8-9.3MHz). Feature Extraction: Various uterine contractility features were extracted from the gathered ultrasound recordings using a quantitative dedicated speckle tracking algorithm previously developed and implemented in Matlab software (Mathworks, Natick, USA). The full details of the methodology of feature extraction have been described in detail in previously published works (221,224,226–229). Simply put, speckle tracking measures the displacement of image ‘speckles’ (such as those seen in various shades of grey on ultrasound images) over time. Speckle movement reflects movement of the imaged tissue, which in this case is movement of the uterine myometrium. For each ultrasound recording, a grid of tracking markers was manually positioned over the uterine junctional zone along the endometrium, known to be the most contractile part of the uterus (see Figure 6.2 for an illustrative example). Grid markers were placed 5 mm from the fundus along the endometrial border. The grid markers were coupled in pairs, and distance and strain signals were derived between each pair in both the longitudinal and radial direction (See Figure 6.3). Several contraction features were extracted from the measured strain signals as described below. Previous analyses of inter and intra-observer variability in the placement of the grid markers showed a high level of correlation, making the method both reproducible and reliable (229), see appendix 6A.
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