Quantitative assessment of human cervix with correlation length ratio during pregnancy: An in vivo longitudinal study

Abstract

We recently introduced a novel parameter called the correlation length ratio (CLR), a ratio of lateral to axial correlation lengths for backscattered echo signals, to detect the presence of elongated structures in soft tissues. Here, we look at variation of CLR and presence of elongated structures in human cervix during pregnancy using a longitudinal data from a group of women with normal pregnancy. Thirty women, ages ranging from 19 to 37years, were scanned with ultrasound at five time points beginning at their normal first-trimester screening (8 –13 weeks) through term pregnancy (nominally 40 week). We computed correlation lengths, and CLR. To account for the system point spread function, an empirical cumulative distribution function of the CLR was obtained from a reference phantom. A one-sided threshold of 95% of the CDF was then computed. The difference between CLR in the sample and the threshold was computed and its variation with increasing gestational age was obtained. CLR estimation demonstrated a gradient along the length of the cervix. This longitudinal study also demonstrated an increase of about 0.5% (per week) in lateral correlation length and 0.8% increase in CLR with increasing gestational age, while axial correlation length was almost constant.