In vivo ultrasonic attenuation slope estimates for detecting cervical ripening in rats: Preliminary results

Abstract

To effectively postpone preterm birth, cervical ripening needs to be detected and delayed. As the cervix ripens, the spacing between the collagen fibers increases and fills with water, hyaluronan, decorin, and enzymes suggesting that the ultrasonic attenuation of the cervix should decrease. The decrease in ultrasonic attenuation may be detectable, leading to an effective means of detecting cervical ripening. Herein, the traditional attenuation slope-estimation algorithm based on measuring the downshift in center frequency of the ultrasonic backscattered signal with propagation depth was modified and applied to the cervix of rats. The modified algorithm was verified using computer simulations and an ex vivo tissue sample before being evaluated in in vivo animal studies. Sphericallyfocused f/3 transducers with 33-MHz center frequencies and with 9-mm focal lengths were used in both the simulations and experiments. The accuracy was better than 15% in the simulations, and the attenuation slope of the cervix in the ex vivo experiment was 2.6±0.6 dB/cm-MHz, which is comparable to 2.5±0.4 dB/cm-MHz measured using a through-transmission insertion loss technique. For the in vivo experiments, a statistically significant effect of ultrasonic attenuation with gestational age was not observed. The large variances in the in vivo results were most likely due to the natural variation in attenuation for biological tissue between animals.

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.…”

“…Studies have shown that as the delivery time approaches, the collagen rich cervix is filled with water and enzymes which results in a lower attenuation value and a softening of the cervix. Our earlier work showed that attenuation of the cervix decreased as the cervix prepared for delivery [8][9][10][11][12]. The softening of the cervix can also be quantified using shear wave elastography [13][14][15].…”

“…Both of these changes should result in a lower ultrasound attenuation as has been shown in our earlier work. [8][9][10][11][12].…”

Spatial and Frequency Compounding in Application to Attenuation Estimation in Tissue

“…It has been also reported that the attenuation coefficient differs for cancerous and healthy tissue (Saijo, Sasaki, 1996). Moreover, the noninvasive determination of ultrasonic attenuation enables to predict the premature delivery in rats and humans (Bigelow et al, 2008;McFarlin et al, 2010). These reports motivate us to search for efficient methods of unambiguous attenuation estimation to be used in ultrasonic (US) imaging.…”

Tissue Attenuation Estimation from Backscattered Ultrasound Using Spatial Compounding Technique - Preliminary Results

“…Saijo and Sasaki (1996) employed scanning acoustic microscope to measure five types of gastric cancer and indicated different attenuation coefficients and sound speeds comparing to normal tissue. Bigelow et al (2008) investigated possibility of prediction of the premature delivery based on the noninvasive ultrasonic attenuation determination. In many other publications it has been reported that pathological processes can lead to changes in the mean attenuation coefficient that range from several percent for cirrhotic human liver, through dozens percent for fatty human liver (Lu et al, 1999), or degenerated bovine articular cartilage (Nieminen et al, 2004) to over a hundred percent in case of porcine liver HIFU treatment in vivo (Zderic et al, 2004) or two hundred percent for porcine kidney thermal coagulation (Worthington, Sherar, 2001).…”