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As the cervix prepares for delivery, the spacing between the collagen fibers increases and fills with water, hyaluronan, decorin, and enzymes suggesting that the ultrasonic attenuation should decrease as has been demonstrated in our earlier studies. However, earlier results had significant variability, making change in cervical attenuation to assess the risk of premature delivery difficult. Ultrasonic attenuation is the loss of energy within a specific region of interest. Our goal was to reduce the variability in the attenuation estimates by considering the scattering assumptions.
The scatterer approximations made when deriving the theory are satisfied if the signal-to-noise ratio (SNR) of the speckle statistics was approximately 1.9. In this study, we compared the attenuation estimates obtained without considering the scattering properties to the estimates obtained when we restricted our attention to images where the SNR of the speckle pattern was 1.7 to 2.1. The ultrasound echoes were obtained from transvaginal ultrasound scans performed on timed pregnant Sprague-Dawley rats at gestational ages between 12 and 21 days. Each rat was scanned multiple times throughout the course of their pregnancy with a 40-MHz custom intravaginal transducer.
As the cervix remodeled to prepare for labor, there was a significant decrease in ultrasonic attenuation.
The change in the ultrasonic attenuation of the cervix with increasing gestational age was much more definitive and consistent when considering the SNR of the speckle. A significant reduction of the SNR below 1.9 might be attributed to a change in ultrasonic scattering properties due to tissue features such as blood vessels which would violate scattering assumptions. Therefore, consideration of the speckle properties might allow for improved diagnosis of the risk of premature delivery in the future. Ultrasonic attenuation has the potential to be used clinically to detect cervix tissue property changes signaling the onset of labor. (Supported by NIH Grants 1R21HD058705, R37EB002641, and Iowa State University)