Quantitative ultrasound imaging and characterization of uterine peristaltic waves

Uterine peristalsis (UP) plays an important role in the generation of intrauterine streams; upstream towards the ovaries to support conception and downstream to favor menstrual emptying. Our understanding of the uterine mechanical behavior is however hampered by a lack of quantitative analysis, limiting diagnosis and treatment of several uterine dysfunctions. Building on our recent work on dedicated speckle tracking for uterine strain analysis, here we present the first algorithm for spatiotemporal assessment of UP. In particular, we aim at characterizing the propagation of contraction waves along the uterus. Nine healthy women were scanned by B-mode transvaginal ultrasound during the late follicular phase of the menstrual cycle. This phase coincides with the fertile period and is known to be the most active. The speckle was tracked on the gray-level videos by optical flow. Tracking accuracy was further improved by an adaptive spatial-warping approach. The method was first optimized and validated with a dedicated setup producing controlled motion on an ex-vivo uterus. In vivo, a grid of points with regular spacing was positioned above and below the endometrial contour, and tracked over time to generate a time-space representation of the strain rate along the endometrium. This representation was then analyzed in the k-space for the assessment of UP (contraction wave) velocity and direction, determined by the two dominant spectral peaks.