Hemorrhage correlation with total energy and surface power near opossum skull exposed to pulsed ultrasound

High intensity focused ultrasound (HIFU) has been used noninvasively for therapeutic applications. Previous studies have shown that HIFU when targeted on fetal rat and mice bones resulted in hemorrhage. Hemorrhage occurrence and area were found to correlate with total equivalent energy (i.e. product of energy density, number of pulses and volume of the focal region) and surface power (i.e. product of pulse average intensity, number of pulses and beam area). Continuation of the trend was observed in Opossum pups. Opossum pups (7- 8 post natal days) were exposed to 1.1 MHZ f/1 spherically focused transducer (6.3 cm focal length). Three groups of n=8 and a control group of n=8 were exposed to rarefactional pressure of 6, 4.5, 3.6 MPa with ITA values of 10.78, 5.39, 6.74 W/cm2. PRF was varied by 500, 500, 1000 Hz with an exposure duration of 2 to 4 minutes. Dependence of hemorrhage on total energy and surface power suggests mechanical failure to be a possible mechanism

Using speckle statistics to improve attenuation estimates for cervical assessment

Preterm birth is a major contributor to infant mortality worldwide. Cervical length and previous history of preterm birth are the only two indicators which can help in identifying preterm birth but have a low positive identifying rate. Quantitative ultrasound parameters like attenuation can provide additional details about the tissue microstructure besides the diagnostic image. Attenuation can be used to detect preterm cases as the attenuation decreases with the increasing gestation age and this decrease can be seen earlier in cases of preterm birth. The algorithm and the size of the region of interest (ROI) play a vital role in calculating valid estimates of attenuation. In this paper, we compared the ability of the Spectral log difference algorithm and the Spectral difference algorithm to detect changes in the cervix leading to delivery for both full term and preterm births under varying ROI sizes. Spectral log difference yields a more consistent decrease in the attenuation as we approach delivery for both the preterm and full term patients. ROI size doesn\u27t significantly alter the observed trends for this study. For preterm birth a maximum decreases of 0.35dB/cm-MHz was observed. The bias in attenuation algorithms can be removed by selecting homogenous regions inside the cervix, but the cervix is a heterogeneous tissue. Gamma mixture model is used to segment the cervix into different tissue types and attenuation algorithm are then applied to individual tissue type to get an estimate of attenuation. The area under the receiver operating characteristic curve increases from 56% to 80% when gamma mixture model is used for segmentation

Development of an Ultrasonic Method to Detect Cervical Remodeling in Vivo in Full-Term Pregnant Women

The objective of this study was to determine whether estimates of ultrasonic attenuation could detect changes in the cervix associated with medically induced cervical remodeling. Thirty-six full-term pregnant women underwent two transvaginal ultrasonic examinations separated in time by 12 h to determine cervical attenuation, cervical length and changes thereof. Ultrasonic attenuation and cervical length data were acquired from a zone (Zonare Medical Systems, Mountain View, CA, USA) ultrasound system using a 5–9 MHz endovaginal probe. Cervical attenuation and cervical length significantly decreased in the 12 h between the pre-cervical ripening time point and 12 h later. The mean cervical attenuation was 1.1 ± 0.4 dB/cm-MHz before cervical ripening agents were used and 0.8 ± 0.4 dB/cm-MHz 12 h later (p \u3c 0.0001). The mean cervical length also decreased from 3.1 ± 0.9 cm before the cervical ripening was administered to 2.0 ± 1.1 cm 12 h later (p \u3c 0.0001). Cervical attenuation and cervical length detected changes in cervical remodeling 12 h after cervical ripening administration

Beyond Cervical Length: A Pilot Study of Ultrasonic Attenuation for Early Detection of Preterm Birth Risk

The purpose of this study was to determine whether cervical ultrasonic attenuation could identify women at risk of spontaneous preterm birth. During pregnancy, women (n = 67) underwent from one to five transvaginal ultrasonic examinations to estimate cervical ultrasonic attenuation and cervical length. Ultrasonic data were obtained with a Zonare ultrasound system with a 5- to 9-MHz endovaginal transducer and processed offline. Cervical ultrasonic attenuation was lower at 17–21 wk of gestation in the SPTB group (1.02 dB/cm-MHz) than in the full-term birth groups (1.34 dB/cm-MHz) (p = 0.04). Cervical length was shorter (3.16 cm) at 22–26 wk in the SPTB group than in the women delivering full term (3.68 cm) (p = 0.004); cervical attenuation was not significantly different at this time point. These findings suggest that low attenuation may be an additional early cervical marker to identify women at risk for SPTB

Ultrasonic Attenuation and Backscatter Coefficient Estimates of Rodent-Tumor-Mimicking Structures: Comparison of Results among Clinical Scanners

In vivo estimations of the frequency-dependent acoustic attenuation (α) and backscatter (η) coefficients using radiofrequency (rf) echoes acquired with clinical ultrasound systems must be independent of the data acquisition setup and the estimation procedures. In a recent in vivo assessment of these parameters in rodent mammary tumors, overall agreement was observed among α and η estimates using data from four clinical imaging systems. In some cases, particularly in highly-attenuating heterogeneous tumors, multisystem variability was observed. This paper compares α and η estimates of a well-characterized rodent-tumor-mimicking homogeneous phantom scanned using seven transducers with the same four clinical imaging systems: a Siemens Acuson S2000, an Ultrasonix RP, a Zonare Z.one and a VisualSonics Vevo2100. α and η estimates of lesion-mimicking spheres in the phantom were independently assessed by three research groups, who analyzed their system\u27s rf echo signals. Imaging-system-based estimates of α and η of both lesion-mimicking spheres were comparable to through-transmission laboratory estimates and to predictions using Faran\u27s theory, respectively. A few notable variations in results among the clinical systems were observed but the average and maximum percent difference between α estimates and laboratory-assessed values was 11% and 29%, respectively. Excluding a single outlier dataset, the average and maximum average difference between η estimates for the clinical systems and values predicted from scattering theory was 16% and 33%, respectively. These results were an improvement over previous interlaboratory comparisons of attenuation and backscatter estimates. Although the standardization of our estimation methodologies can be further improved, this study validates our results from previous rodent breast-tumor model studies

Cross-imaging system comparison of backscatter coefficient estimates from a tissue-mimicking material

A key step toward implementing quantitative ultrasound techniques in a clinical setting is demonstrating that parameters such as the ultrasonic backscatter coefficient (BSC) can be accurately estimated independent of the clinical imaging system used. In previous studies, agreement in BSC estimates for well characterized phantoms was demonstrated across different laboratory systems. The goal of this study was to compare the BSC estimates of a tissue mimicking sample measured using four clinical scanners, each providing RF echo data in the 1-15 MHz frequency range. The sample was previously described and characterized with single-element transducer systems. Using a reference phantom for analysis, excellent quantitative agreement was observed across the four array-based imaging systems for BSC estimates. Additionally, the estimates from data acquired with the clinical systems agreed with theoretical predictions and with estimates from laboratory measurements using single-element transducers

Using speckle statistics to improve attenuation estimates for cervical assessment

Preterm birth is a major contributor to infant mortality worldwide. Cervical length and previous history of preterm birth are the only two indicators which can help in identifying preterm birth but have a low positive identifying rate. Quantitative ultrasound parameters like attenuation can provide additional details about the tissue microstructure besides the diagnostic image. Attenuation can be used to detect preterm cases as the attenuation decreases with the increasing gestation age and this decrease can be seen earlier in cases of preterm birth. The algorithm and the size of the region of interest (ROI) play a vital role in calculating valid estimates of attenuation. In this paper, we compared the ability of the Spectral log difference algorithm and the Spectral difference algorithm to detect changes in the cervix leading to delivery for both full term and preterm births under varying ROI sizes. Spectral log difference yields a more consistent decrease in the attenuation as we approach delivery for both the preterm and full term patients. ROI size doesn't significantly alter the observed trends for this study. For preterm birth a maximum decreases of 0.35dB/cm-MHz was observed. The bias in attenuation algorithms can be removed by selecting homogenous regions inside the cervix, but the cervix is a heterogeneous tissue. Gamma mixture model is used to segment the cervix into different tissue types and attenuation algorithm are then applied to individual tissue type to get an estimate of attenuation. The area under the receiver operating characteristic curve increases from 56% to 80% when gamma mixture model is used for segmentation.</p