The dominant fiber direction <i>θ</i> in the outer radial zone in four quadrants for all specimens imaged.

<p>Each circle represents the dominant fiber directions in one quadrant. Each line represents one cervical sample averaged across all 400 μm × 400 μm radial subregions, with the line color representing the standard deviation (SD) between the radial subregions. Red represents higher SD and blue represents lower SD. Posterior and anterior quadrants both have more uniform dominant directions among samples (lines having a narrower spread) and within a single specimen there is lower SD between the radial subregions (lines having a bluish color). Left and right quadrants have a wider spread of the dominant fiber direction between samples, and within an individual sample, fiber directions also change more dramatically along radial direction.</p

The average of SD of the concentration parameter <i>b</i> between different radial subregion.

<p>This figure is color-coded such that red represents higher SD (relative heterogeneity of <i>b</i> along radial direction) and blue represents lower SD (relative homogeneity of <i>b</i> along radial direction). The highest value appears in the A quadrant of NP samples and the lower values appear in the L quadrant of NP samples and P/L quadrants of PG samples.</p

A pixel-wise directionality map on an <i>en face</i> image parallel from and 245 μm beneath the cut surface (Specimen 1 in Table 1).

<p>(A) directionality map with locations of 400 μm × 400 μm subregions corresponding to 80 pixels × 80 pixels.; (B) OCT image within the white box in (A); (C) directionality map within the white box in (B). Pixels with no fiber information are coded in black. Each 400 μm × 400 μm subregion represents a location for the fiber orientation and dispersion analysis in the A (anterior), P (posterior), L (left), and R (right) quadrants. Along the radial direction, the boxes are divided into inner region (red) and outer region (green).</p

Representative fiber distributions found in the upper cervix and corresponding 2D von-Mises fits.

<p>The dominant direction <i>θ</i> is shown by dotted line. All four subregions are taken from the outer radial zone of the same NP sample (Specimen 5 in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0166709#pone.0166709.t001" target="_blank">Table 1</a>). A subregion with (A) a single family of fibers that have the most alignment (<i>b</i> = 0.820) and (B) highly dispersed fibers that are randomly oriented in the plane. A subregion with (C) two fiber families and (D) three fiber families. (Note: current distribution fitting methodology cannot distinguish the multiple fiber families.)</p

The anatomical position of the cervix, sample preparation and terms.

<p>(A) The anatomical position of the uterus and the cervix produced from an MRI of a patient at 22 weeks of gestation [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0166709#pone.0166709.ref004" target="_blank">4</a>]. The proximal end of the cervix is the internal os and the distal end of the cervix is the external os. (B) Illustration of specimen preparation of the upper cervix. The cervix is cut perpendicular to the inner canal to obtain slices for experiments. The sliced cervix in (B) is oriented the same as shown in (A). The imaging direction is perpendicular to cutting direction, normal to cervical slices. (C) Illustration of four anatomical quadrants (A-anterior, P-posterior, L-left, and R-right), inner and outer radial zones, and 400μm × 400μm subregions used for fiber dispersion analysis.</p

SD of dominant direction <i>θ</i> (unit: rad) in different parity groups and pregnancy statuses.

<p>Results from each quadrant in the outer radial zone and some combinations are shown. NP groups do not have significant differences among themselves. Between NP groups and PG, the only significant difference is found between primiparous NP and PG when P/A quadrants are combined (<i>p</i> = 0.004). Unlike the analysis for <i>b</i>, nulliparous NP (<i>p</i> = 0.276) and multiparous NP (<i>p</i> = 0.143) do not have a significant difference with PG in the SD of <i>θ</i>. No significant difference is found in L/R quadrants.</p

Patient demographics of specimens used for this study.

<p>Patient demographics of specimens used for this study.</p

Representative OCT <i>en face</i> images and overlaid fiber orientation maps of cervical slices with different inner zone widths.

<p>(A), (C), (E), and (G) are OCT <i>en face</i> images taken 245 μm beneath the cut surface and (B), (D), (F), and (H) are overlaid fiber orientation maps. (A), (C), and (E) were from non-pregnant patients with wide, narrow, and no inner zones. (G) was from a pregnant patient. The white line sketches the inner canal. The red contour delineates the inner radial zone according to local fiber orientation. The yellow bars in (B), (D), (F), and (H) show local dominant fiber orientation in each 400 × 400 μm sub-region. (A)-(B), (C)-(D), (E)-(F), and (G)-(H) are Speicemen 1, Speciemen 2, Speciemen 3, and Speciemen 13 in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0166709#pone.0166709.t001" target="_blank">Table 1</a> respectively.</p

The concentration parameter <i>b</i> averaged for all 400 μm × 400 μm radial subregions in each quadrant for all NP and PG specimens.

<p>This figure is color-coded such that blue represents higher <i>b</i> (lower dispersion and more aligned fibers) and red represents lower <i>b</i> (more dispersed and randomly oriented fibers). Overall, the collagen fibers of the NP cervices had tighter aligned fibers within the 400 μm × 400 μm subregions compared to the PG samples. Within the NP samples, the A/P quadrants in the outer zone have the most aligned fibers within the 400 μm × 400 μm radial subregions compared to the rest.</p

The average of the SD of dominant fiber direction <i>θ</i> between radial subregions for NP and PG specimens.

<p>Values are shown in eight regions that include the inner and outer radial zones of four quadrants. Each region is color-coded such that red represents higher SD (more heterogeneous <i>θ</i> between radial subregions) and blue represents lower SD (more homogeneous <i>θ</i> between radial subregions). The anterior and posterior quadrants of the NP cervical tissue samples have more homogeneous circumferential fibers compared to its left and right quadrants.</p