Optimization of Ultrasound Backscatter Spectroscopy to Assess Neurotoxic Effects of Anesthesia in the Newborn Non-human Primate Brain.

Studies in animal models have revealed that long exposures to anesthetics can induce apoptosis in the newborn and young developing brain. These effects have not been confirmed in humans because of the lack of a non-invasive, practical in vivo imaging tool with the ability to detect these changes. Following the successful use of ultrasound backscatter spectroscopy (UBS) to monitor in vivo cell death in breast tumors, we aimed to use UBS to assess the neurotoxicity of the anesthetic sevoflurane (SEVO) in a non-human primate (NHP) model. Sixteen 2- to 7-day-old rhesus macaques were exposed for 5 h to SEVO. Ultrasound scanning was done with a phased array transducer on a clinical ultrasound scanner operated at 10 MHz. Data consisting of 10-15 frames of radiofrequency (RF) echo signals from coronal views of the thalamus were obtained 0.5 and 6.0 h after initiating exposure. The UBS parameter "effective scatterer size" (ESS) was estimated by fitting a scattering form factor (FF) model to the FF measured from RF echo signals. The approach involved analyzing the frequency dependence of the measured FF to characterize scattering sources and selecting the FF model based on a χ2 goodness-of-fit criterion. To assess data quality, a rigorous acceptance criterion based on the analysis of prevalence of diffuse scattering (an assumption in the estimation of ESS) was established. ESS changes after exposure to SEVO were compared with changes in a control group of five primates for which ultrasound data were acquired at 0 and 10 min (no apoptosis expected). Over the entire data set, the average measured FF at 0.5 and 6.0 h monotonically decreased with frequency, justifying fitting a single FF over the analysis bandwidth. χ2 values of a (inhomogeneous continuum) Gaussian FF model were one-fifth those of the discrete fluid sphere model, suggesting that a continuum scatterer model better represents ultrasound scattering in the young rhesus brain. After application of the data quality criterion, only 5 of 16 subjects from the apoptotic group and 5 of 5 subjects from the control group fulfilled the acceptance criteria. All subjects in the apoptotic group that passed the acceptance criterion exhibited a significant ESS reduction at 6.0 h. These changes (-6.4%, 95% Interquartile Range: -14.3% to -3.3%) were larger than those in the control group (-0.8%, 95% Interquartile Range: -2.0% to 1.5%]). Data with a low prevalence of diffuse scattering corresponded to possibly biased results. Thus, ESS has the potential to detect changes in brain microstructure related to anesthesia-induced apoptosis.

Quantitative assessment of cervical softening during pregnancy in the Rhesus macaque with shear wave elasticity imaging.

Abnormal parturition, e.g. pre- or post-term birth, is associated with maternal and neonatal morbidity and increased economic burden. This could potentially be prevented by accurate detection of abnormal softening of the uterine cervix. Shear wave elasticity imaging (SWEI) techniques that quantify tissue softness, such as shear wave speed (SWS) measurement, are promising for evaluation of the cervix. Still, interpretation of results can be complicated by biological variability (i.e. spatial variations of cervix stiffness, parity), as well as by experimental factors (i.e. type of transducer, posture during scanning). Here we investigated the ability of SWEI to detect cervical softening, as well as sources of SWS variability that can affect this task, in the pregnant and nonpregnant Rhesus macaque. Specifically, we evaluated SWS differences when imaging the cervix transabdominally with a typical linear array abdominal transducer, and transrectally with a prototype intracavitary linear array transducer. Linear mixed effects (LME) models were used to model SWS as a function of menstrual cycle day (in nonpregnant animals) and gestational age (in pregnant animals). Other variables included parity, shear wave direction, and cervix side (anterior versus posterior). In the nonpregnant cervix, the LME model indicated that SWS increased by 2% (95% confidence interval 0-3%) per day, starting eight days before menstruation. During pregnancy, SWS significantly decreased at a rate of 6% (95% CI 5-7%) per week (intracavitary approach) and 3% (95% CI 2-4%) per week (transabdominal approach), and interactions between the scanning approach and other fixed effects were also significant. These results suggest that, while absolute SWS values are influenced by factors such as scanning approach and SWEI implementation, these sources of variability do not compromise the sensitivity of SWEI to cervical softening. Our results also highlight the importance of standardizing SWEI approaches to improve their accuracy for cervical assessment.

Pacific Hurricane Landfalls on Mexico and SST.

A statistical model of Northeast Pacific tropical cyclones (TCs) is developed and used to estimate hurricane landfall rates along the coast of Mexico. Mean annual landfall rates for 1971-2014 are compared to mean rates for the extremely high Northeast Pacific sea-surface temperature (SST) of 2015. Over the full coast, the mean rate and 5%-95% uncertainty for Saffir-Simpson category one and higher TCs (category-1+ TCs) is 1.241.051.33yr-1 for 1971-2014 and 1.690.892.08yr-1 for 2015, a difference that is not significant. However, the increase for the most intense landfalls, category-5 TCs, is significant: 0.0090.0060.011yr-1 for 1971-2014 and 0.0310.0160.036yr-1 for 2015. The SST impact on the category-5 TC landfall rate is largest on the northern Mexican coast. The increased landfall rates for category-5 TCs is consistent with independent analysis showing that SST has its greatest impact on the formation rates of the most intense Northeast Pacific tropical cyclones. Landfall rates on Hawaii ( 0.0330.0190.045yr-1 for category-1+ TCs and 0.0100.0050.016yr-1 for category-3+ TCs for 1971-2014) show increases in the best estimates for 2015 conditions, but the changes are insignificant according to our tests.

Acoustic elastography under dynamic compression using one-dimensional track motion.

This work provides an detailed analysis of a method for ultrasound-based elasticity image formation using dynamic compression technique. Radiofrequency (RF) data acquired from a homogenous phantom, where both mechanical and acoustic proprieties were set equivalent to biologic tissues, were used to validate our results. Local strains were obtained by speckle tracking of the acoustic scatterers motion between a pair of RF echo fields acquired when the phantom was dynamically deformed at low frequency (approximately 1 Hz). In this work we investigated the dynamic compression technique as an alternate to the conventional quasi-static compression. In particular, we studied the improvement on strain estimation by varying the size of 1-D kernel during the tracking between the pre- and pos-deformed RF fields.