Eileen Hwuang^{1}, M. Dylan Tisdall^{1}, Nadav Schwartz^{1}, John A. Detre^{1}, and Walter R. Witschey^{1}

While measuring uterine artery (UtA) impedance is commonly used to assess for risk of preeclampsia and intrauterine growth restriction, little is understood about the remodeling process during gestation. An improved understanding of geometrical changes can lead to predictive biomarkers of adverse pregnancies. Here we present a method of measuring path length and curvature of the tortuous UtAs by segmentation and centerline extraction of time-of-flight MR angiography. We show in 8 pregnant subjects in the 2^{nd} and 3^{rd} trimester that this technique is feasible for investigating longitudinal trends of UtA remodeling and cases of maladaptation.

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Figure 1: a) 3D maximum intensity projection
of the TOF angiogram in a representative subject. The green arrowheads
delineate the UtAs after branching from the internal iliac arteries. b) The
isosurface and centerline extraction of the same subject. Red dots represent
the starting landmarks at the bifurcation of the internal and external iliac
arteries. Black dots represent the ending landmarks at the most inferior point
of the UtAs. The path length and root mean squared curvature reported in this
study are calculated from the blue coordinates. C) Diagram of curvature
computation based on the osculating circle, r=radius, κ=curvature.

Figure 2: a) Centerlines of Subject G with
difference in tortuosity between the left and right UtA. It extends from the
descending aorta through the common iliac arteries, internal iliac arteries, UtAs,
and external iliac arteries. Red dots represent the starting landmarks at the
bifurcation of the internal and external iliac arteries. Black dots represent
the ending landmarks at the most inferior point of the UtAs. The curvature
histogram of the right UtA (b) has a narrower distribution than the left UtA
(c).

Figure 3: This table reports data from the eight
subjects analyzed in this study with gestational age, maternal age, maternal
height, gravidity, parity, measurements of path length between the landmarks
annotated in Fig. 1b, and root mean squared (RMS) curvature between the
landmarks (R = right, L = left).

Figure 4: Plot with linear correlation
results showing increasing trend in path length over gestational age (GA) in
the left UtA and right UtA.

Figure 5: Plot with linear correlation
results showing curvature with decreasing trend with gestational age (GA) in
the left UtA and right UtA.