Estimate of the attenuation coefficient using a clinical array transducer for the detection of cervical ripening in human pregnancy

Abstract

Premature delivery is the leading cause of infant mortality in the United States. Currently, premature delivery cannot be prevented and new treatments are difficult to develop due to the inability to diagnose symptoms prior to uterine contractions. Cervical ripening is a long period that precedes the active phase of uterine contractions and cervical dilation. The changes in the microstructure of the cervix during cervical ripening suggest that the ultrasonic attenuation should decrease. The objective of this study is to use the reference phantom algorithm to estimate the ultrasonic attenuation in the cervix of pregnant human patients. Prior to applying the algorithm to in vivo human data, two homogeneous phantoms with known attenuation coefficients were used to validate the algorithm and to find the length and the width of the region of interest (ROI) that achieves the smallest error in the attenuation coefficient estimates. In the phantom data, we found that the errors in the attenuation coefficients estimates are less than 12% for ROIs that contain 40 wavelengths or more axially and 30 echo lines or more laterally. The reference phantom algorithm was then used to obtain attenuation maps of the echoes from two human pregnant cervices at different gestational ages. It was observed that the mean of the attenuation coefficient estimates in the cervix of the patient at a more advanced gestational age is smaller than the mean of the attenuation coefficient estimates in the cervix of the patient at an earlier gestational age which suggests that ultrasonic attenuation decreases with increasing gestational age. We also observed a large variance between the attenuation coefficient estimates in the different regions of the cervix due to the natural variation in tissue microstructures across the cervix. The preliminary results indicate that the algorithm could potentially provide an important diagnostic tool for diagnosing the risk of premature delivery.

Using speckle statistics to improve attenuation estimates for cervical assessment

“…We can rewrite equation The size of the ROI was varied in both the axial and lateral direction. Our previous studies have shown that approximately 15 pulse lengths in the axial direction and 15 pulse lengths in the axial direction and 15 echoes in the lateral direction gave a standard deviation on the order of 25% in the attenuation estimates for simulations, phantom experiments, and in the rat cervix when using the spectral log difference algorithm, while the spectral difference algorithm had a standard deviation of less than 13% for the same ROI size [9,37,39].The pulse length was calculated by taking the auto correlation coefficient of time samples from RF echo lines of the phantom data. Samples with absolute correlation coefficient greater than 0.2 were considered correlated and determined the time pulse length.…”

“…Our previous studies had shown that approximately 15 pulse lengths in the axial direction and 15 echoes in the lateral direction gave a standard deviation on the order of 25% in the attenuation estimates when the tissue was homogeneous. Therefore, we varied our region sizes about these values for our study [11,37,39].…”

“…A hybrid algorithm was proposed which combines the spectral difference and spectral shift algorithms to reduce the impact of diffraction, system dependent parameters, and variations in backscatter at boundaries [36]. simulated a comparison between spectral difference, spectral log and hybrid method to conclude that there was not a significant difference in performance between hybrid and spectral log difference in terms of dependence on changing scattering properties and ROI size [37]. For the purpose of this study, only spectral difference and spectral log difference algorithms were studied.…”

Improving the quality of attenuation imaging using full angular spatial compounding

“…The attenuation coefficient slope (ACS), combined with other statistical parameters and tissue properties (i.e., image texture, backscatter coefficients), has been used to diagnose diffuse liver diseases [1,2] and characterize breast tissues [3]. Attenuation coefficients have been proposed as potential tools for predicting cervical ripening in rats [4] and humans [5]. The possibility to differentiate between Graves' and Hashimoto's thyroid disease based on ACS estimates has been explored [6].…”

Quantitative ultrasound backscatter parameters in the human cervix

“…[6] In addition, ultrasonic attenuation has been shown to decrease with increasing gestational age. [7] However, the effects of the angle of interrogation of the beam, position within the cervix, parity, and ripening of the nonpregnant cervix have not been reported.…”