Ultrasonic attenuation estimation of the pregnant cervix: a preliminary report

OBJECTIVE

Estimates of ultrasonic attenuation (the loss of energy as an ultrasonic wave propagates through tissue) have been used to evaluate the structure and function of tissues in health and disease. The purpose of this research was to develop a method to estimate ultrasonic cervical attenuation during human pregnancy using a clinical ultrasound system.

METHODS

Forty women underwent a cervical scan once during pregnancy with the Zonare z.one clinical ultrasound system using a 4-9-MHz endovaginal transducer. This ultrasound system provides access to radiofrequency (RF) image data for processing and analysis. In addition, a scan of a tissue-mimicking phantom with a known attenuation coefficient was acquired and used as a reference. The same settings and transducer used in the clinical scan were used in the reference scan. Digital data of the beam-formed image were saved in Digital Imaging and Communications in Medicine (DICOM) format on a flash drive and converted to RF data on a personal computer using a Matlab program supplied by Zonare. Attenuation estimates were obtained using an algorithm that was independently validated using tissue-mimicking ultrasonic phantoms.

RESULTS

RF data were acquired and analyzed to estimate attenuation of the human pregnant cervix. Regression analysis revealed that attenuation was: a predictor of the interval from ultrasound examination to delivery (beta = 0.43, P = 0.01); not a predictor of gestational age at time of examination (beta = - 0.23, P = 0.15); and not a predictor of cervical length (beta = 0.077, P = 0.65).

CONCLUSIONS

Ultrasonic attenuation estimates have the potential to be an early and objective non-invasive method to detect interval between examination and delivery. We hypothesize that a larger sample size and a longitudinal study design will be needed to detect gestational age-associated changes in cervical attenuation.

Encapsulated contrast microbubble radial oscillation associated with postexcitation pressure peaks

This work combines modeling and experiment to assess encapsulated microbubble oscillations associated with broadband pressure peaks detected after microbubble excitation (postexcitation signals). Data were acquired from albumin-shelled and phospholipid-shelled microbubbles using a passive cavitation detector consisting of a confocally aligned 2.8-MHz transmitter and 13-MHz receiver. Microbubbles in weak solutions were insonified with a 5-cycle pulse at a peak rarefactional pressure of 2.0+/-0.2 MPa. For each microbubble type, at least 100 received signals were identified as individual-microbubble responses. The average broadband noise from signals with postexcitation response was 4.2-7.2 dB higher than from signals without postexcitation. Pressure-time responses for each microbubble type were simulated using the model by Marmottant et al. [J. Acoust. Soc. Am. 118, 3499-3505 (2005)], with insonification conditions matching the experiment. Increased broadband noise predicted for microbubbles with postexcitation response was consistent with that observed experimentally (4.0-8.9 dB). The model predicted that postexcitation signals occur only when the radial oscillation exceeds both the shell break-up threshold and twice the initial radius (free bubble inertial cavitation threshold).

A two-microphone dual delay-line approach for extraction of a speech sound in the presence of multiple interferers

This paper describes algorithms for signal extraction for use as a front-end of telecommunication devices, speech recognition systems, as well as hearing aids that operate in noisy environments. The development was based on some independent, hypothesized theories of the computational mechanics of biological systems in which directional hearing is enabled mainly by binaural processing of interaural directional cues. Our system uses two microphones as input devices and a signal processing method based on the two input channels. The signal processing procedure comprises two major stages: (i) source localization, and (ii) cancellation of noise sources based on knowledge of the locations of all sound sources. The source localization, detailed in our previous paper [Liu et al., J. Acoust. Soc. Am. 108, 1888 (2000)], was based on a well-recognized biological architecture comprising a dual delay-line and a coincidence detection mechanism. This paper focuses on description of the noise cancellation stage. We designed a simple subtraction method which, when strategically employed over the dual delay-line structure in the broadband manner, can effectively cancel multiple interfering sound sources and consequently enhance the desired signal. We obtained an 8-10 dB enhancement for the desired speech in the situations of four talkers in the anechoic acoustic test (or 7-10 dB enhancement in the situations of six talkers in the computer simulation) when all the sounds were equally intense and temporally aligned.

Superthreshold behavior and threshold estimates of ultrasound-induced lung hemorrhage in adult rats: role of beamwidth

It is well documented that ultrasound-induced lung hemorrhage can occur in mice, rats, rabbits, pigs, and monkeys. The objective of this study was to assess the role of the ultrasound beamwidth (beam diameter incident on the lung surface) on lesion threshold and size. A total of 144 rats were randomly exposed to pulsed ultrasound at three exposure levels and four beamwidths (12 rats per group). The three in situ peak rarefactional pressures were about 5, 7.5, and 10 MPa. The four 19-mm-diameter focused transducers had measured pulse-echo -6-dB focal beamwidths of 470 microm (2.8 MHz; f/1), 930 microm (2.8 MHz; f/2), 310 microm (5.6 MHz; f/1), and 510 microm (5.6 MHz; f/2). Exposure durations were 10 s, pulse repetition frequencies were 1 kHz, and pulse durations were 1.3 micros (2.8 MHz; f/1), 1.2 micros (2.8 MHz; f/2), 0.8 micros (5.6 MHz; f/1) and 1.1 micros (5.6 MHz; f/2). The lesion surface area and depth were measured for each rat as well as the percentage of rats with lesions per group. Logistic regression analysis and Gaussian-Tobit analysis methods were used to analyze the data. The effects of in situ peak rarefactional pressure and beamwidth were highly significant, but ultrasonic frequency was not significant. In addition, the estimated interaction between in situ peak rarefactional pressure and beamwidth was positive and highly significant. The ultrasound beamwidth incident on the lung surface was shown to strongly affect the percentage and size of ultrasound-induced lung hemorrhage lesions. Even though ultrasonic frequency was an experimental variable, it was not shown to affect the lesion percentage or size.

Cardiopulmonary function in rats with lung hemorrhage induced by pulsed ultrasound exposure

OBJECTIVE

To assess cardiopulmonary function in rats exposed to pulsed ultrasound using superthreshold exposure conditions known to produce significant lung hemorrhage.

METHODS

In 1 group of 9 anesthetized Sprague-Dawley rats, 5 foci of ultrasound-induced hemorrhage were produced in the left lung of each rat. In a second group of 6 rats, 5 foci of ultrasound-induced hemorrhage were produced in the left and right lungs of each rat. Each lesion was induced using superthreshold pulsed ultrasound exposure conditions (3.1-MHz center frequency, 1.7-kHz pulse repetition frequency, 1.3-micro-second pulse duration, 60-second exposure duration, 39-MPa in situ peak compressional pressure, and 17-MPa in situ peak rarefactional pressure). After exposure, the lungs were fixed in formalin and assessed histologically. The total lesion volume was calculated for each lesion in each lung lobe. Measurements of cardiopulmonary function included assessment of pulsatile arterial pressure, heart rate, end-tidal carbon dioxide, respiratory rate, and arterial blood gases (PCO2 and PO2). Functional data were quantified before (baseline) and 30 minutes after exposure to ultrasound.

RESULTS

In the 9 rats that had lesions in only the left lung, the mean (SEM) lesion volume was 97 (13) mm3 and represented about 3.4% of the total lung volume. In the 6 rats that had lesions in both the left and right lungs, the left, right, and total mean lesion volumes, respectively, were 102 (16), 114 (11), and 216 (18) mm3 and represented about 3.7%, 4.2%, and 7.9% of the total lung volume. There were no statistically significant differences in cardiopulmonary measurements between baseline values and values obtained after exposure to ultrasound in the 9 rats exposed on the left lung only. The 6 rats exposed bilaterally had statistically significant differences in arterial pressure (134 +/- 4 versus 113 +/- 9 mm Hg; P= .047) and arterial PO2 (70 +/- 5 versus 58 +/- 4 mm Hg; P = .024) between baseline values and values obtained after exposure to ultrasound.

CONCLUSIONS

The severity of ultrasound-induced lesions produced in 1 lung did not affect measurements of cardiopulmonary function because of the functional respiratory reserve in the unexposed lung. However, when both the left and right lungs had ultrasound-induced lesions, the functional respiratory reserve was decreased to a point at which rats were unable to maintain systemic arterial pressure or resting levels of arterial PO2.

A real-time approach to detect seal defects in food packages using ultrasonic imaging

The microbial integrity of many types of flexible food packages depends on a zero defect level in the fused seam seal. Human inspection for defects in these seals is marginal at best, and secondary incubation protocols are often used to spot packages with compromised integrity before releasing product for sale. A new type of inspection method has been developed and is being evaluated for robustness. The purpose of the study was to evaluate a new raster scanning geometry to simulate continuous motion, online ultrasonic inspection of the seal region in flexible food package seals. A principal engineering tradeoff of scanning inspection systems is between increased line speed that results from decreased spatial sampling (less acquired data to process) and decreased image quality. The previously developed pulse-echo Backscattered Amplitude Integral (BAI) mode imaging technique is used to form ultrasound images using the new scanning geometry. At an ultrasonic frequency of 22.9 MHz, 38- and 50-microm-diameter air-filled channel defects in all-plastic transparent trilaminate are evaluated. The contrast-to-noise ratio (CNR) of the processed BAI-mode image is used to quantify image quality as a function of spatial sampling. Results show seal defects (38- and 50-microm diameter) are still detectable for undersampled conditions, although image quality degrades as spatial sampling decreases. Further, it is concluded that the raster scanning geometry is feasible for online inspection.

Propagation speed of sound assessment in the layers of the guinea-pig esophagus in vitro by means of acoustic microscopy

The study's purpose was to evaluate the propagation speed of sound in the tissue layers of the esophagus at various mechanical loadings. Scanning laser acoustics microscopy was applied for the estimation of the propagation speed in the mucosa-submucosa and muscle layers of guinea-pig esophagus in vitro (n = 26). The propagation speed in the esophagus was determined in the no-load state with all external forces removed, and in the distended and zero-stress states. The zero-stress state was obtained by cutting the esophageal rings radially. The propagation speed in the no-load state differed significantly (p < 0.001) between the muscle layer (median 1740, quartiles 1735-1746 m/s) and the mucosa (1607, 1605-1609 m/s). In the distended state the propagation speed in the muscle layer decreased significantly (p < 0.001) to 1673 (1666-1681) m/s while it did not change significantly in mucosa (1602, 1600-1607 m/s). When compared to the no-load state, the propagation speed in the zero-stress state in the muscle layers decreased to 1624 (1615-1636) m/s (p < 0.001) and in mucosa to 1584 (1566-1603) m/s (p < 0.001). In conclusion, the esophagus is a composite structure with heterogeneous propagation speed characteristics. Furthermore, the mechanical loading state must be considered in esophageal ultrasound studies.

Temporal and spatial evaluation of lesion reparative responses following superthreshold exposure of rat lung to pulsed ultrasound

This study characterized the reparative responses in rat lung. Forty-five adult female rats were exposed at two sites over the left lung to 3.1-MHz superthreshold pulsed ultrasound. The repair of lung lesions was evaluated from 0 through 44 days postexposure. Macroscopic lesions at 0 days postexposure were large bright red ellipses of hemorrhage. By 1 and 3 days postexposure, lesions were the same size and dark red to red-black, but, by 3 days postexposure, lesions had a raised surface appearance. From 5 to 10 days postexposure, lesions grew smaller in size, progressed from red-gray to yellow-brown, and retained a raised surface appearance. From 13 through 44 days postexposure, lesions gradually decreased in size, had a faint yellow-brown discoloration, and gradually lost the raised surface appearance. By 37 and 44 days postexposure, lung returned to near normal morphology, but had small areas of light yellow-brown discoloration in the areas where lung was exposed. Microscopic lesions at 0 and 1 days postexposure were areas of acute alveolar hemorrhage. By 3 days postexposure, lesions had loss of alveolar erythrocytes and the formation of hemoglobin crystals. From 5 through 44 days postexposure, iron in degraded erythrocytes was processed to hemosiderin and was negligible in quantity at 44 days postexposure. The proliferation of resident cells (likely alveolar epithelial cells, fibroblasts and endothelial cells) and the infiltration of inflammatory cells in lesions declined in intensity as the lesions aged and was minimal by 44 days postexposure. Under the superthreshold exposure conditions described, lesions induced by ultrasound do not seem to have long-term residual effects in lung.

Quantifying B-mode images of in vivo rat mammary tumors by the frequency dependence of backscatter

OBJECTIVE

To evaluate the frequency dependence of ultrasonic backscatter for its ability to differentiate between neoplastic and healthy tissue.

METHODS

Standard B-mode images were created of 5 rats with spontaneous mammary tumors, and regions of interest in the lesion and surrounding tissue were parameterized by the slope of the backscatter amplitude versus frequency.

RESULTS

In 4 of the 5 rats, the averaged backscatter slope of the regions of interest in the tumor was significantly (P < .05) different from that of the surrounding tissue, and the fifth case had a moderate difference (P = .20). The consistency of the averaged slope values (1.2-1.8 dB/MHz) across all but 1 of the mammary tumors was encouraging for the prospect of identifying a tissue type by its backscatter slope.

CONCLUSIONS

This work suggests that characterization and diagnosis of tissue types may be possible by using ultrasonographic images quantified by the frequency dependence of backscatter.

Attenuation coefficient estimates of mouse and rat chest wall

Attenuation coefficients of intercostal tissues were estimated from chest walls removed postmortem (pm) from 41 6-to-7-week-old female ICR mice and 27 10-to-11-week-old female Sprague-Dawley rats. These values were determined from measurements through the intercostal tissues, from the surface of the skin to the parietal pleura. Mouse chest walls were sealed in plastic wrap and stored at 4 degrees C until evaluated, and rat chest walls were sealed in Glad-Lock Zipper sandwich bags, and stored at -15 degrees C. When evaluated, chest wall storage time ranged between 1 and 2 days pm for mice and between 41 and 110 days pm for rats. All chest walls were allowed to equilibrate to 22 degrees C in a water bath prior to evaluation. For both mouse and rat intercostal tissues, the estimated frequency normalized attenuation coefficient was 1.1 dB/cm-MHz. In order to determine if there was an effect of storage time on estimates of attenuation coefficient, an independent experiment was conducted. The intercostal tissues from six mouse chest walls were evaluated at three time points (1, 22, and 144 days pm), and from six rat chest walls were evaluated at four time points (1, 22, 50, and 125 days pm). There was no difference in the estimated intercostal tissue attenuation coefficient as a function of time postmortem.

Superthreshold behavior and threshold estimation of ultrasound-induced lung hemorrhage in adult mice and rats

Threshold estimates and superthreshold behaviors for ultrasound-induced lung hemorrhage were investigated as a function of species (adult mice and rats) and ultrasound frequency (2.8 and 5.6 MHz). A total of 151 6-to-7-week-old female ICR mice and 160 10-to-11-week-old female Sprague-Dawley rats were randomly divided into two ultrasonic frequency groups, and further randomly divided into seven or eight ultrasonic peak rarefactional pressure groups. Each group consisted of about 10 animals. Animals were exposed to pulsed ultrasound at either 2.8-MHz center frequency (1-kHz PRF, 1.42-microsecond pulse duration) or 5.6-MHz center frequency (1-kHz PRF, 1.17-microsecond pulse duration) for a duration of 10 seconds. The in situ (at the pleural surface) peak rarefactional pressure levels ranged between 2.5 and 10.5 MPa for mice and between 2.3 and 11.3 MPa for rats. The mechanical index (MI) ranged between 1.4 and 6.3 at 2.8 MHz for mice and between 1.1 and 3.1 at 5.6 MHz for rats. The lesion surface area and depth were measured for each animal as well as the percentage of animals with lesions per group. The characteristics of the lesions produced in mice and rats were similar to those described in previous studies by our research group and others, suggesting a common pathogenesis in the initiation and propagation of the lesions at the gross and microscopic levels. The percentage of animals with lesions showed no statistical differences between species or between ultrasound frequencies. These findings suggest that mice and rats are similar in sensitivity to ultrasound-induced lung damage and that the occurrence of lung damage is independent of frequency. Lesion depth and surface area also showed no statistically significant differences between ultrasound frequencies for mice and rats. However, there was a significant difference between species for lesion area and a suggestive difference between species for lesion depth. The superthreshold behavior of lesion area and depth showed that rat lung had more damage than mouse lung, and the threshold estimates showed a weak, or lack of, frequency dependency, suggesting that the MI is not consistent with the observed findings.

Superthreshold behavior of ultrasound-induced lung hemorrhage in adult mice and rats: role of pulse repetition frequency and exposure duration

Superthreshold behavior for ultrasound-induced lung hemorrhage was investigated in adult mice and rats at an ultrasound center frequency of 2.8 MHz to assess the role of pulse repetition frequency and exposure duration. One hundred fifty, 6-7-week-old female ICR mice and 150 10-11-week-old female Sprague-Dawley rats were each divided into 15 exposure groups (10 animals per group) for a 3 x 5 factorial design (3 exposure durations of 5, 10, and 20 s and 5 pulse repetition frequencies of 25, 50, 100, 250, and 500 Hz). The in situ (at the pleural surface) peak rarefactional pressure of 12.3 MPa and the pulse duration of 1.42 micros were the same for all ultrasonically-exposed animals. In addition, 15 sham exposed mice and 15 sham exposed rats were included into both studies. In each study of 165 animals, the exposure conditions were randomized. The lesion depth and surface area were measured for each animal, as well as the percentage of animals with lesions per group. The characteristics of the lesions produced in mice and rats were similar to those described in studies by our research group and others, suggesting a common pathogenesis for the initiation and propagation of the lesions at the gross and microscopic levels. The proportion of lesions in both species was related statistically to pulse repetition frequency (PRF) and exposure duration (ED), with the exception that PRF in rats was not quite significant; the PRF x ED interaction (number of pulses) for lesion production was not significant for either species. The PRF, but not ED, significantly affected lesion depth in both species; the PRF x ED interaction for depth was not significant for either species. Both PRF and ED significantly affected lesion surface area in mice, while neither affected area in rats; the PRF x ED interaction for surface area was not significant for either species.

Localization of multiple sound sources with two microphones

This paper presents a two-microphone technique for localization of multiple sound sources. Its fundamental structure is adopted from a binaural signal-processing scheme employed in biological systems for the localization of sources using interaural time differences (ITD). The two input signals are transformed to the frequency domain and analyzed for coincidences along left/right-channel delay-line pairs. The coincidence information is enhanced by a nonlinear operation followed by a temporal integration. The azimuths of the sound sources are estimated by integrating the coincidence locations across the broadband of frequencies in speech signals (the "direct" method). Further improvement is achieved by using a novel "stencil" filter pattern recognition procedure. This includes coincidences due to phase delays of greater than 2pi, which are generally regarded as ambiguous information. It is demonstrated that the stencil method can greatly enhance localization of lateral sources over the direct method. Also discussed and analyzed are two limitations involved in both methods, namely missed and artifactual sound sources. Anechoic chamber tests as well as computer simulation experiments showed that the signal-processing system generally worked well in detecting the spatial azimuths of four or six simultaneously competing sound sources.

Ultrasound-induced lung hemorrhage is not caused by inertial cavitation

In animal experiments, the pathogenesis of lung hemorrhage due to exposure to clinical diagnostic levels of ultrasound has been attributed to an inertial cavitation mechanism. The purpose of this article is to report the results of two experiments that directly contradict the hypothesis that ultrasound-induced lung hemorrhage is caused by inertial cavitation. Elevated hydrostatic pressure was used to suppress the involvement of inertial cavitation. In experiment one, 160 adult mice were equally divided into two hydrostatic pressure groups (0.1 or 1.1 MPa), and were randomly exposed to pulsed ultrasound (2.8-MHz center frequency, 1-kHz PRF, 1.42-micros pulse duration, 10-s exposure duration). For the two hydrostatic pressure groups (80 mice each), 8 in situ peak rarefactional pressure levels were used that ranged between 2.82 and 11.8 MPa (10 mice/group). No effect of hydrostatic pressure on the probability of hemorrhage was observed. These data lead to the conclusion that lung hemorrhage is not caused by inertial cavitation. Also, the higher hydrostatic pressure enhanced rather than inhibited the impact of ultrasonic pressure on the severity (hemorrhage area, depth, and volume) of lesions. These counterintuitive findings were confirmed in a second experiment using a 2 x 5 factorial design that consisted of two ultrasonic pressure levels and five hydrostatic pressure levels (100 mice, 10 mice/group). If inertial cavitation were the mechanism responsible for lung hemorrhage, then elevated hydrostatic pressures should have resulted in less rather than more tissue damage at each ultrasonic pressure level. This further supports the conclusion that the pathogenesis of ultrasound-induced lung hemorrhage is not caused by inertial cavitation.

Ultrasound-induced lung hemorrhage is not caused by inertial cavitation

In animal experiments, the pathogenesis of lung hemorrhage due to exposure to clinical diagnostic levels of ultrasound has been attributed to an inertial cavitation mechanism. The purpose of this article is to report the results of two experiments that directly contradict the hypothesis that ultrasound-induced lung hemorrhage is caused by inertial cavitation. Elevated hydrostatic pressure was used to suppress the involvement of inertial cavitation. In experiment one, 160 adult mice were equally divided into two hydrostatic pressure groups (0.1 or 1.1 MPa), and were randomly exposed to pulsed ultrasound (2.8-MHz center frequency, 1-kHz PRF, 1.42-micros pulse duration, 10-s exposure duration). For the two hydrostatic pressure groups (80 mice each), 8 in situ peak rarefactional pressure levels were used that ranged between 2.82 and 11.8 MPa (10 mice/group). No effect of hydrostatic pressure on the probability of hemorrhage was observed. These data lead to the conclusion that lung hemorrhage is not caused by inertial cavitation. Also, the higher hydrostatic pressure enhanced rather than inhibited the impact of ultrasonic pressure on the severity (hemorrhage area, depth, and volume) of lesions. These counterintuitive findings were confirmed in a second experiment using a 2 x 5 factorial design that consisted of two ultrasonic pressure levels and five hydrostatic pressure levels (100 mice, 10 mice/group). If inertial cavitation were the mechanism responsible for lung hemorrhage, then elevated hydrostatic pressures should have resulted in less rather than more tissue damage at each ultrasonic pressure level. This further supports the conclusion that the pathogenesis of ultrasound-induced lung hemorrhage is not caused by inertial cavitation.

Acoustic imaging of objects buried in soil

In this study, we demonstrate an acoustic system for high-resolution imaging of objects buried in soil. Our goal is to image cultural artifacts in order to assess in a rapid manner the historical significance of a potential construction site. We describe the imaging system and present preliminary images produced from data collected from a soil phantom. A mathematical model and associated computer software are developed in order to simulate the signals acquired by the system. We have built the imaging system, which incorporates a single element source transducer and a receiver array. The source and receiver array are moved together along a linear path to collect data. Using this system, we have obtained B-mode images of several targets by using delay-and-sum beamforming, and we have also applied synthetic aperture theory to this problem.

Determination of biomechanical properties in guinea pig esophagus by means of high frequency ultrasound and impedance planimetry

Impedance planimetry and high-frequency ultrasound were used to determine circumferential stress and strain from measurements of luminal cross-sectional area and wall thickness during balloon distension of the guinea pig esophagus in vitro (N = 30). The excised esophagus was mounted on two plastic tubes in an organ bath containing oxygenated calcium-free Krebs-Ringer solution with 10(-2) M MgCl2 to abolish smooth muscle contractile activity. One of the plastic tubes was movable in order to stretch the esophagus longitudinally by 15% (elongated state). The impedance planimetry probe was placed with the balloon inside the lumen of the esophagus. A 20-MHz ultrasound transducer was mounted above the esophagus and provided scans in the transverse and longitudinal directions. The luminal cross-sectional area at the highest applied pressure of 2.9 kPa was 13.3 +/- 0.3 mm2 in the resting state. In the elongated state the luminal cross-sectional area at the highest pressure was 12.5 +/- 0.1 mm2 (P < 0.02). The wall thickness decreased from 990 +/- 21 microm at 0 kPa to 640 +/- 9 microm at 2.9 kPa at in vitro length. In the elongated state, the values were 940 +/- 32 microm to 480 +/- 13 microm (P < 0.01). The stress-strain relation was exponential (sigma = alpha(ebetaepsilon - 1), r2 > 0.98, P < 0.01). The circumferential elastic modulus calculated at a Green strain of 0.95 was 44.5 +/- 10.5 kPa in the in vitro state and 81.7 +/- 13.1 kPa in the elongated state. The elastic modulus differed between the resting and elongated states (P < 0.02).

Analysis of resolution for an amplitude-steered array

In 1976, Hughes and Thompson introduced the idea of steering the maximum response of a linear array by amplitude weighting the output signals of the elements, thus eliminating the need for time delays or phase-shift networks. Currently that amplitude-steered array concept is being extended to a broadband two-dimensional array that can be used for real-time three-dimensional imaging. In shifting the use of the amplitude-steered array from underwater acoustic communications to imaging, we must consider different issues of the array's performance such as lateral and axial resolution. For the linear amplitude-steered array, we show that both lateral and axial resolution are limited by the length of the array. The dependence of axial resolution on the length of the array is a unique feature of the amplitude-steered array, leading to an interesting tradeoff between lateral and axial resolution. A theoretical basis for the dependence is developed and simulation results are given.

Anisotropy of ultrasonic propagation and scattering properties in fresh rat skeletal muscle in vitro

The anisotropy of frequency-dependent backscatter coefficient, attenuation, and speed of sound is assessed in fresh rat skeletal muscle within 5 h post-mortem. Excised rat semimembranosus and soleus muscles are measured in 37 degrees C Tyrode solution, with the muscle fibers at 90 degrees and 45 degrees orientations to the incident sound beam. Reflected and through transmission signals from either a 6- or 10-MHz focused transducer give frequency dependent information in the 4-14 MHz range. The attenuation coefficient in each muscle is consistently a factor of 2.0 +/- 0.4 lower for propagation perpendicular to the fibers than at 45 degrees, whereas speed of sound shows a much milder anisotropy, and is slightly faster for the 90 degrees orientation. The largest anisotropy is seen in the backscatter coefficient, most notably in the semimembranosus where the magnitude at 90 degrees is over an order of magnitude greater than at 45 degrees, with the frequency dependence in both cases giving a power law between 1.5 and 2.0.

Interlaboratory comparison of ultrasonic backscatter, attenuation, and speed measurements

In a study involving 10 different sites, independent results of measurements of ultrasonic properties on equivalent tissue-mimicking samples are reported and compared. The properties measured were propagation speed, attenuation coefficients, and backscatter coefficients. Reasonably good agreement exists for attenuation coefficients, but less satisfactory results were found for propagation speeds. As anticipated, agreement was not impressive in the case of backscatter coefficients. Results for four sites agreed rather well in both absolute values and frequency dependence, and results from other sites were lower by as much as an order of magnitude. The study is valuable for laboratories doing quantitative studies.

In vivo ultrasonographic exposimetry: human tissue-specific attenuation coefficients in the gynecologic examination

OBJECTIVE

The purpose of the current study was to determine in vivo, tissue-specific ultrasonic attenuation coefficients for each of the tissue layers comprising the anterior abdominal wall, uterus, and vagina with use of a quantitative multilayer tissue model. We wanted to validate the "homogeneous" tissue model-based Food and Drug Administration derating factor of 0.3 dB/cm-MHz applied to obstetric-use ultrasonography systems.

STUDY DESIGN

With use of a 3. 0-MHz mechanical sector scanner and our previously tested exposimetry equipment, we obtained a set of at least 5 separate acoustic pressure waveforms from each test subject by placing a calibrated 7-element linear-array hydrophone in the anterior vaginal fornix while she was undergoing transabdominal ultrasonography. Corresponding sets of reference in vitro acoustic pressure waveforms were also recorded for each test subject in a 37 degrees C water bath. All linear measurements of individual layer thicknesses and total distances were made on-line with use of electronic calipers. A set of multiple and independent insertion loss values, denoted ILn, was calculated for path n between the abdominal surface and the hydrophone from n sonograms for each test subject. Each tissue layer type was identified and its thickness along each path n was measured. The thickness of tissue type m along path n was denoted by dnm. The only unknown quantities left were the attenuation coefficients Am of each of the m tissue layers for that test subject. The overestimated set of equations dnm Am = ILn was solved for Am with use of a nonnegative least-squares solution technique.

RESULTS

With use of data from 162 independent insertion loss estimate paths, the overall tissue-specific attenuation coefficients for each of the tissue layer types, expressed as mean value +/- SD, were 2.3 +/- 1.5 dB/cm-MHz for the skin and subcutaneous layer, 3.1 +/- 2.5 dB/cm-MHz for skeletal muscle, 0.6 +/- 0.5 dB/cm-MHz for myometrium, and 3.6 +/- 2.7 dB/cm-MHz for the vaginal wall. The overall insertion loss assuming the "homogeneous" tissue model was 0.7 +/- 0.3 dB/cm-MHz.

CONCLUSIONS

We have determined the specific ultrasonic attenuation coefficients for each of the tissue layers comprising the anterior abdominal wall, uterus, and vagina and validated the Food and Drug Administration derating factor of 0.3 dB/cm-MHz applied to obstetric use ultrasonography systems. Of all the models proposed, the "homogeneous" tissue model appears to be the best model for determining ultrasonic exposure risk during reproductive ultrasonographic examinations.

Detection of lines and boundaries in speckle images--application to medical ultrasound

This paper describes an approach to boundary detection in ultrasound speckle based on an image enhancement technique. The enhancement algorithm works by filtering the image with "sticks," short line segments which are varied in orientation to achieve the maximum projected value at each point. The statistical properties of this approach have been described in an earlier paper; in this work we present three significant extensions to improve the performance of the basic method. First, we investigate the effect of varying the size and shape of the sticks. We show that these variations affect the performance of the algorithm in very fundamental ways, for example by making it more or less sensitive to thinner or more tightly curving boundaries. Second, we present a means of improving the performance of this technique by estimating the distribution function of the orientation of the line passing through each point. Finally, we show that images can be "stained" for easier visual interpretation by applying to each pixel a false color whose hue is related to the orientation of the most prominent line segment at that point. Examples are given to illustrate the performance of the different settings on a single image.

Behavioral effects of prenatal exposure to pulsed-wave ultrasound in unanesthetized rats

The present experiment examined the developmental neurotoxicity of pulsed-wave (pw) ultrasound in rats, using an exposure system designed to eliminate restraint or anesthesia from the exposure conditions. Pregnant Sprague-Dawley CD rats trained to remain immobile in a water-filled ultrasound exposure tank were scanned with 3-MHz pw ultrasound at spatial peak temporal average intensities (ISPTA) of 0, 2, 20, or 30 W/cm2 on embryonic days 4-20 for approximately 10 min/day. The data showed that such insonation produced no adverse effects on maternal weight gain or reproductive outcome, nor on the postnatal growth or survival of the offspring. No exposure-related alterations in behavioral development were observed in the offspring of rats scanned with pw ultrasound during gestation. In addition, there was no consistent evidence of an ultrasound-associated change in the adult offspring behaviors tested; i.e., no treatment effects were found on measures of locomotor activity, water maze learning, and acoustic startle reactivity. An effect on tactile startle was observed on some trials in the low exposure group male offspring, but this effect was neither dose dependent nor consistent with any other finding. Overall, these results indicate that the neurobehavioral development of rats was not altered by prenatal exposure to pw ultrasound at ISPTA levels of up to 30 W/cm2.

Rabbit and pig lung damage comparison from exposure to continuous wave 30-kHz ultrasound

Previous comparative studies of ultrasound-induced pulmonary hemorrhage in mice and rabbits suggested that sensitivity to damage was species dependent (O'Brien and Zachary 1994b). In order to understand better these differences in species more analogous to the human, 74 pigs and 75 rabbits were each exposed for 10 min at 1 of 6 acoustic pressure levels (0, 145, 290, 340 [rabbits only], 460 and 490 [pigs only] kPa) at an ultrasonic frequency of CW 30 kHz. Eighteen mice were used as positive controls (10-min duration at 145 kPa). Because pig lung has numerous physiological and anatomical similarities to human lung, it was selected as the appropriate animal model for these studies. Pig lung data were compared to rabbit lung data; rabbit lung data have already been compared with mouse lung data (O'Brien and Zachary 1994a). Comparative analyses and extrapolation of these experimental data are intended to provide a better scientific basis for understanding the potential biological effects of ultrasound on human lungs since such studies will probably never be conducted with humans. Under the same exposure conditions and lung assessment criteria, mouse lung was determined to be more sensitive to ultrasound-induced damage than that of the rabbit by a factor of 3.9, the rabbit lung was more sensitive to ultrasound-induced damage than that of the pig by a factor of 3.7, and the mouse lung was more sensitive to ultrasound-induced damage than that of the pig by a factor of 14.4.

Guided tissue regeneration using a biodegradable barrier membrane for new attachment: a clinical, histologic, and histometric study in dogs

Although nonbiodegradable barrier membranes have proven partially successful in achieving regeneration of lost periodontium through the principles of guided tissue regeneration, their use requires a second surgical procedure for their removal. The results of a study, in which a biodegradable collagen membrane was used to treat dehiscence defects in dogs, are presented. The membrane was an effective barrier to the downgrowth of gingival epithelium during the early stages of healing and tended to increase the regeneration of new cementum and connective tissue attachment. It was also biocompatible and biodegradable.

Performance of ultrasonic speckle tracking in various tissues

The purpose of this study was to investigate the accuracy of ultrasound speckle tracking in various tissues. Results from two-dimensional tissue speckle tracking in liver, muscle, fat, and sponge samples are presented, while keeping other speckle tracking parameters constant. Speckle tracking performance was characterized both in terms of the magnitude of tracking errors and in terms of the percentage of correctly tracked displacement vectors. Speckle tracking in muscle tissue, which contains myofibrils and significant tissue microstructure, produced the highest percentage of correctly tracked vectors and smallest tracking errors relative to other tissues.

In situ human obstetrical ultrasound exposimetry: estimates of derating factors for each of three different tissue models

A specialized in vivo exposimetry system was developed to acquire transabdominal in situ ultrasound exposure quantities in obstetric patients. Under surgical conditions, the sterilized 7-element calibrated linear array hydrophone was introduced into the uterus under direct ultrasound guidance and placed in direct contact with the products of conception, usually in the saggital midplane of the uterine cavity. Twenty-five patients with empty bladders and 10 patients with full bladders were studied at gestational ages between 7 and 20 weeks. In the empty bladder condition, the sound beam traversed the anterior abdominal wall, uterus, amniotic fluid and fetal parts and in the full bladder condition, the sound beam also traversed the fluid-filled bladder. Each study was conducted with a 3 MHz, mechanical sector transducer in combination with an ATL Ultramark 4 diagnostic ultrasound imaging system. Calibration data were recorded after completion of each in vivo patient study. The acquired exposimetry data from the 35 obstetric patients were used to evaluate the appropriateness of three tissue attenuation models, viz., fixed path, homogeneous and overlying. All three tissue models yield a mean attenuation coefficient value of about a factor of 3 to 4 greater than their respective minimum values. In the case of the overlying and homogeneous tissue models, there was a statistically significant correlation between their calculated attenuation coefficients and total distance for the combined data set whereas there was no such dependency for the calculated fixed-path tissue model. In summary, any one of the three tissue models may be used to estimate in utero acoustic quantities during the first and second trimesters of human pregnancy based on this study.

Hematologic and growth-related effects of frequent prenatal ultrasound exposure in the long-tailed macaque (Macaca fascicularis)

Prior investigations have shown that reduced birth weights and transient neutropenias result from frequent exposure of monkey fetuses to ultrasound. To further explore these findings, 26 animals were studied (16 exposed, 10 controls; "triple mode"; ATL Ultramark 9 with HDI; ISPTAd approximately 645 to 714 mW/cm2). Exposures were performed daily for 5 days each week from gestational days (GD) 21 to 35 (5 min), three times weekly from GD 36 to 60 (5 min), then weekly from GD 61 to 153 +/- 1 (10 min). Fetal blood samples (FBS) were collected for complete blood counts (CBCs), hematopoietic progenitor assay, circulating insulin-like growth factors (IGF-I, IGF-II) and binding proteins (IGFBP-3) (GD 120, 140, 153 +/- 1). Animals were delivered by Cesarean section at term (GD 153 +/- 1), and body weights, morphometrics, CBCs, and bone marrow aspirates assessed at delivery and postnatally for 3 months. Fetal neutropenias were noted in exposed animals in addition to reduced circulating progenitors (colony forming unit-granulocyte-macrophage [CFU-GM]). Growth of CFU-GM from bone marrow was exuberant at term, whereas circulating levels were diminished comparable to prenatal samples. Exposed animals were smaller at birth; marked reductions in IGFBP-3 were noted prenatally. These data suggest that frequent prenatal ultrasound exposure can transiently alter the neutrophil lineage, although these findings may be the result of enhanced margination and organ sequestration. Data also suggest that transient, altered growth patterns may be due to perturbations of the IGF axis.

Lung lesions induced by continuous- and pulsed-wave (diagnostic) ultrasound in mice, rabbits, and pigs

These studies documented the presence or absence of macroscopic and microscopic intraparenchymal hemorrhage in individual lung lobes of mice, rabbits, and pigs exposed to continuous- and pulsed-wave (diagnostic) ultrasound; we described the character of and lesions associated with the hemorrhage and compared differences in the lesions among species and exposure conditions to investigate the pathogenic mechanisms and species differences associated with ultrasound-induced lung hemorrhage. In a series of three sequential interdependent studies, 312 mice, 91 rabbits, and 74 pigs were divided at random into experimental groups and exposed to continuous-wave ultrasound (3 kHz modulated at 120 Hz) of acoustic pressure levels ranging from 0 to 490 kPa for 5, 10, or 20 minutes. In a fourth study, three mice, 43 rabbits, and six pigs were divided at random into experimental groups and exposed to pulsed-wave ultrasound (3- and 6-MHz center frequency) of peak rarefactional acoustic pressure levels ranging from 0 to 5.6 MPa for 5 minutes. Macroscopic lesions induced by continuous- and pulsed-wave ultrasound consisted of dark red to black areas of hemorrhage that extended from visceral pleural surfaces into lung parenchyma. Hemorrhage appeared spatially related to the edges of lung lobes where pleura of dorsal and ventral surfaces met, occurred in specific lung lobes in all three species, and appeared anatomically related to lung that was closest to and in contiguous alignment with the ultrasound transducer and thus the path of the sound beam. Macroscopic lesions were similar in all species under all exposure conditions for both continuous- and pulsed-wave ultrasound; however, hemorrhage was not induced in pig lung exposed to pulsed-wave ultrasound at any peak rarefactional acoustic pressure level. Eighteen mice (145 kPa exposure pressure), 60 rabbits (145-460 kPa exposure pressure), and 58 pigs (145-490 kPa exposure pressure) from study 3 were used for microscopic evaluation of lung exposed to continuous-wave ultrasound; three mice (6 MHz; 2.9 and 5.4 MPa), 39 rabbits (3 and 6 MHz; 2.3-5.4 MPa), and six pigs (3 and 6 MHz; 3.3, 5.4, and 5.6 MPa) from study 4 were used for microscopic evaluation of lung exposed to pulsed-wave ultrasound. Microscopic lesions and the character of hemorrhage induced by continuous-wave ultrasound were different from those induced by pulsed-wave ultrasound. Lesions induced by continuous-wave ultrasound under all exposure conditions were similar in all three species. Lesions induced by pulsed-wave ultrasound under all exposure conditions were similar in all three species.(ABSTRACT TRUNCATED AT 400 WORDS)

Relation of ultrasonic backscatter and acoustic propagation properties to myofibrillar length and myocardial thickness

BACKGROUND

Ultrasonic backscatter demonstrates a cardiac cycle-dependent modulation. The exact mechanism of the modulation is under debate. The objective of the present study was to test the hypothesis that a change in size and configuration of myofilaments from systole to diastole alters acoustic propagation properties and backscatter.

METHODS AND RESULTS

In vivo measurements were made of integrated backscatter at 5 MHz (IBR5), followed by in vitro measurements of ultrasonic attenuation, speed, and heterogeneity index using a scanning laser acoustic microscope at 100 MHz. Studies were performed in canine hearts (16) arrested in systole (8) with calcium chloride or arrested in diastole (8) with potassium chloride. Sarcomere length was measured with a calibrated eyepiece on a Ziess microscope. Wall thickness was measured with calipers. The attenuation coefficient of 220 +/- 34 dB/cm during systole was significantly higher than the coefficient of 189 +/- 24 dB/cm during diastole (P < .01); the IBR5 of -44.7 +/- 1.2 dB during systole was significantly greater than the IBR5 of -47.0 +/- 1.0 dB during diastole (P < .01); the ultrasonic speed of 1591 +/- 11 m/s during systole was higher than the speed of 1575 +/- 4.2 m/s during diastole (P < .01); and the heterogeneity index of 7.4 +/- 1.8 m/s during systole was significantly lower than the index of 9.0 +/- 2.0 m/s during diastole (P < .02). The sarcomere length of 1.804 +/- 0.142 microns during diastole was significantly higher than the length of 1.075 +/- 0.177 micron during systole (P < .01). Wall thickness was significantly greater during systole than during diastole (20 +/- 3 versus 9 +/- 3 mm, P < .01).

CONCLUSIONS

Ultrasonic backscatter and propagation properties are directly related to sarcomere length and myocardial thickness and may be responsible for cardiac cycle-dependent variation in backscatter.

Ultrasound tissue displacement imaging with application to breast cancer

A method for quantitative imaging of internal tissue motion based on speckle tracking is described. Tissue displacement images from eight patients with sonographically apparent breast masses are used to illustrate the technique. The local displacement response of tissues surrounding malignant and benign breast masses is compared, testing the hypothesis that altered mechanical properties may result in motion signatures for many soft tissue tumors relative to their host tissue. In addition, the potential or anticipated influence of various biological and physical factors on tissue motion response is discussed.

Acoustic propagation properties of normal, stunned, and infarcted myocardium. Morphological and biochemical determinants

BACKGROUND

Identification of viable but stunned myocardium remains a major problem. Since stunned myocardium results in impairment of myocardial function without any structural damage and infarcted myocardium causes major structural disruption, we postulated that acoustic properties could distinguish between the two insults.

METHODS AND RESULTS

Anesthetized open-chest dogs underwent a total occlusion of the left anterior descending coronary artery for 15 minutes (stunned, n = 7) and 90 minutes (infarcted, n = 8), followed by reperfusion for 3 hours. Circumflex coronary artery perfusion territory (n = 15) served as normal control tissue. Regions of myocardium were quantitatively evaluated with a scanning laser acoustic microscope operating at 100 MHz and a research ultrasound system operating at 4 to 7 MHz. Four ultrasonic parameters were determined: attenuation coefficient (an index of loss per unit distance), speed of propagation, a spatial variation of propagation speed called the heterogeneity index (HI), and ultrasonic backscatter at 5 MHz (IBR5). Myocardial water, lipid, and protein contents of normal, stunned, and infarcted myocardium were also determined. The attenuation coefficient of normal myocardium (179 +/- 20 dB/cm) was significantly greater than that of stunned (136 +/- 7 dB/cm, P < .001) and infarcted (130 +/- 8 dB/cm, P < .001) myocardium. The propagation speed of normal myocardium (1597 +/- 6 m/s) was similar to that of stunned (1600 +/- 6 m/s) and significantly higher than that of infarcted (1575 +/- 7 m/s, P < .001) myocardium. The HI for specimen thicknesses of 75 to 100 microns showed an increase of 33% between normal (5.0 +/- 0.8 m/s) and stunned (7.5 +/- 2.3 m/s, P < .05) myocardium. However, for the infarcted myocardium (5.8 +/- 2.0 m/s), the HI was essentially the same as that of the normal myocardium (5.0 +/- 0.8 m/s). The IBR5 of normal (-47.1 +/- 1.0 dB) was not significantly different from that of stunned myocardium (-46.8 +/- 0.9 dB). The IBR5 of infarcted myocardium (-42.4 +/- 1.0 dB) was significantly greater than that of normal myocardium. Myocardial water and protein contents were similar in the normal and stunned myocardium. Water content in the infarcted myocardium (80.8 +/- 2%) was significantly greater (P < .05) than in the normal (72.7 +/- 1.3%), and protein content of 18.5 +/- 0.7% was significantly lower (P < .05) than the normal (21.4 +/- 0.8%). Lipid content was increased in the stunned (8.5 +/- 0.5%) and virtually absent in the infarcted myocardium (0.8 +/- 0.3%) compared with normal (5.5 +/- 0.6%).

CONCLUSIONS

We conclude that acoustic propagation properties can identify stunned and infarcted myocardium and may be related to biochemical/morphological differences.

Behavioral teratologic effects of prenatal exposure to continuous-wave ultrasound in unanesthetized rats

While there are no known risks associated with diagnostic ultrasound, uncertainty about the safety of prenatal ultrasound exposure remains. The purpose of the present experiment was to evaluate the behavioral teratogenic potential of continuous-wave (cw) ultrasound in rats, in the absence of maternal anesthesia or restraint. Pregnant CD rats, trained to remain immobile in a water-filled ultrasound exposure tank, were scanned with 3 MHz cw ultrasound at levels of 0, 2, 10, 20, or 30 W/cm2 ISPTA (spatial peak, temporal average intensity) on gestational days 4-20 for approximately 10 min/day. Offspring were examined postnatally for survival, growth, physical landmarks of development, behavioral development, and the adult functions of locomotor activity, learning and memory, and startle reactivity. No effects of prenatal ultrasound were found on maternal characteristics, offspring survival or growth, physical or behavioral landmarks of development, or adult tests of passive avoidance or startle. Effects at the highest intensity were obtained on corner and side locomotor activity and in a multiple-T water maze on measures of errors of commission and time spent finding the goal. The results showed that prenatal cw ultrasound in rats can induce effects on some postnatal neurobehavioral functions at high exposure intensities (30 W/cm2), but at lower intensities (2-20 W/cm2) no consistent evidence of neurobehavioral effects was observed.

Teratologic evaluation of rats prenatally exposed to pulsed-wave ultrasound

While there are no known risks associated with diagnostic ultrasound, uncertainty about the safety of prenatal ultrasound exposure remains. The purpose of the present experiment was to evaluate the teratogenic potential of pulsed-wave (pw) ultrasound in rats, in the absence of maternal anesthesia or restraint. Pregnant CD rats, trained to remain immobile in a water-filled ultrasound exposure tank, were scanned with 3-MHz pw ultrasound at levels of 0, 2, 20 or 30 W/cm2 ISPTA (spatial peak, temporal average intensity) on gestational days 4-19 for approximately 10 min/day. Examination of fetuses on E20 revealed no increase in skeletal or visceral malformations in groups exposed to pw ultrasound in utero. The number of implantations/dam was significantly increased in all pw ultrasound exposure groups compared to sham-exposed animals and, in a possibly related finding, resorptions were increased in the two highest exposure groups. Although significantly increased compared to controls, resorption frequencies in these groups were low (< 10%). No exposure-related changes in fetal weights were observed in offspring of rats scanned with pw ultrasound during gestation. The results indicate that, under the conditions described, no overt embryotoxicity is associated with gestational exposure to pw ultrasound intensities of up to 30 W/cm2.

Comparison of mouse and rabbit lung damage exposure to 30 kHz ultrasound

Twenty-four mice and sixteen rabbits were evaluated at one exposure duration (10 min) and at three exposure acoustic pressure levels (0, 100 and 145 kPa) at an ultrasonic frequency of 30 kHz, continuous wave for the purpose of testing whether there was a species difference in the degree of sensitivity to ultrasound-induced lung damage. This study was undertaken because it was hypothesized that the mouse may not be an acceptable or suitable animal model for studies that examine the effects of ultrasound on lung tissue for purposes of extrapolating or estimating the degree of potential damage in other species. The rabbit was selected for comparison to the mouse because the rabbit exhibited sufficient physiological and morphological differences from those of the mouse to test this hypothesis. Using exactly the same exposure conditions and lung assessment criteria, it appeared that the mouse lung was more sensitive to ultrasound-induced damage than that of the rabbit by a factor of between 2.8 and 3.6. Lung lesions in mice and rabbits were similar in character, but were much more severe and extensive in mice. Lesions in both species consisted of intraalveolar hemorrhage that appeared as dark red to red-black areas that were visible on the pleural surfaces and that extend within the lung parenchyma.

Mouse lung damage from exposure to 30 kHz ultrasound

Two hundred and seventy mice were evaluated at three exposure durations (5, 10 and 20 min) and at six peak acoustic pressure levels (0, 65, 80, 87, 100 and 145 kPa) with 15 mice per exposure condition, at an ultrasonic frequency of 30 kHz modulated at 120 Hz. Threshold acoustic pressure levels for hemorrhage in mouse lung exposed for the three exposure durations appear to be in the range of 100 kPa. There did not appear to be a strong dependency on exposure duration. When compared to a study with mice in the megahertz frequency range (Child et al. 1990), it appeared that the threshold values followed a square root of frequency dependency, suggesting that the concept of the Mechanical Index (AIUM/NEMA, 1992), although developed for pulsed ultrasound conditions, may be extended to frequencies well below the diagnostic ultrasound frequency range.

Sonographic heat generation in vivo in the gravid long-tailed macaque (Macaca fascicularis)

Temperature elevations that occur during diagnostic ultrasonic exposure were assessed in vivo in gravid macaques after 10, 20, or 30 min (scan mode; N = 30) or 5, 10, or 15 min (pulsed Doppler; N = 32). Five time points were assessed during the second and third trimesters (gestational days 70 to 150 +/- 2; term, approximately 165 days) using a transient thermocouple technique. Measurements were obtained intracranially or at the muscle-bone interface using a commercial sector scanner (ATL MK 600, 7.5 MHz scanhead; scan mode, ISPTA) = 27 mW/cm2, ISPPA = 85 W/cm2, pulse repetition frequency (PRF) = 1 kHz; pulsed Doppler - ISPTA = 54 mW/cm2, ISPPA = 1.5 W/cm2, PRF = 18.5 kHz). Overall, the greatest temperature elevation achieved with either modality or location was 0.6 degrees C.

Evaluation of the bioeffects of prenatal ultrasound exposure in the cynomolgus macaque (Macaca fascicularis): III. Developmental and hematologic studies

The multiple applications of diagnostic ultrasound in obstetrics have resulted in a continued rise in the prenatal population exposed each year. Although human epidemiologic and experimental studies with various animal models have not consistently documented any significant, reproducible findings related to clinically relevant exposures, technologic changes in scanning equipment and gaps in our knowledge regarding the interaction(s) of ultrasound with tissues emphasize the need to pursue safety issues. Studies with nonhuman primates have provided information on the potential for pre and postnatal effects on offspring exposed repeatedly during gestation (ATL MK 600, 7.5 MHz, ISPTA = 27 mW/cm2; ISPPA = 85 W/cm2; Estimated power = 12 mW--scanned for 10 min 5 times weekly gestational day [GD] 20-35; 3 times weekly GD 36-60; once weekly for 20 min GD 60-150). These studies have indicated transient effects on body weight, white blood cell counts (WBCs), and muscle tone postnatally. In an effort to confirm these findings and focus on hematologic changes, a second series of studies was initiated using the same exposure conditions (N = 22; 11 exposed, 11 sham controls). Data derived from both studies were combined and confirmed transient reductions in body weights for infants up through 4 months of age (P < or = 0.03); no statistically significant differences in muscle tone were noted. Similar to the original findings, WBCs were transiently reduced on days 3 (P < or = 0.02) and 21 (P < or = 0.05); prenatal sampling indicated a significant difference between the groups on GD 140 (P < or = 0.04). No direct effects were evident in bone marrow aspirates collected on postnatal days 3, 9, and 21 +/- 1. Although animals were able to compensate for these observed changes and remained unaffected by their occurrence, additional studies will be required to further our understanding of this phenomenon.

A flexible blood flow phantom capable of independently producing constant and pulsatile flow with a predictable spatial flow profile for ultrasound flow measurement validations

The validation of the ultrasound time-domain correlation method of measuring blood flow has required the development of a flexible blood flow phantom capable of generating predictable flow profiles under a wide variety of conditions. The purpose of the phantom is to generate flow with well-known flow properties and not to mimic actual in vivo vessels. This paper describes a flow phantom which can independently generate both constant and pulsatile flow over a wide range of flow rates with a spatially fully developed laminar flow profile. It incorporates a computer-controlled pulsatile pump, which can produce different temporal pulsatile waveforms. The flow phantom also supports multiple vessels, different vessel sizes, as well as different attenuating media. The fluid most commonly used in the phantom is Sephadex mixed with water, and the probability density function of ultrasound reflected from Sephadex is experimentally determined and compared with that of blood. Examples of different constant and pulsatile flow experiments using the phantom are presented.

A teratologic evaluation of continuous-wave, daily ultrasound exposure in unanesthetized pregnant rats

Pregnant Sprague-Dawley rats were trained to remain immobile when placed in water in an ultrasound exposure tank and exposed to 0, 0.1, 2.0, or 30.0 W/cm2 ISPTA (spatial peak, temporal average), 3.0-MHz continuous wave (cw) ultrasound on embryonic (E) days 4-19 for approximately 15 min/day. On E20 fetuses were removed; weighed; examined for external, skeletal, and visceral malformations; and uteri were examined for resorptions. Analyses revealed no increase in pre-implantation loss and no effects on maternal body weight, food, or water consumption. No increase in skeletal or visceral malformations was found, in fact exposed groups had a lower incidence of defects than controls. A significant increase in resorptions in the lowest exposure group (0.1 W/cm2) was obtained, but the effect was isolated, non-dose dependent and not credible as a treatment-related effect. No reduction in fetal weight was obtained, in fact the lowest (0.1-W/cm2) and middle (2.0-W/cm2) exposure level groups weighed slightly more than controls. The immobility procedure succeeded in avoiding anesthetization or forced restraint of the dams, thereby eliminating these factors as potential confounders. The results demonstrated that in unanesthetized, unrestrained rats in utero exposure to incident intensities of ultrasound of up to 30.0 W/cm2 cw ultrasound (or estimated internal exposures of 4-21 W/cm2, depending on body orientation to the incident beam) produced no evidence of embryotoxicity based on fetal necropsy data.

Quantitative assessment of the germicidal efficacy of ultrasonic energy

Propagated (free-field) ultrasonic energy at a frequency of 26 kHz was used to expose aqueous suspensions of bacteria (Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Pseudomonas aeruginosa), fungus (Trichophyton mentagrophytes), and viruses (feline herpesvirus type 1 and feline calicivirus) to evaluate the germicidal efficacy of ultrasound. There was a significant effect of time for all four bacteria, with percent killed increasing with increased duration of exposure, and a significant effect of intensity for all bacteria except E. coli, with percent killed increasing with increased intensity level. There was a significant reduction in fungal growth compared with that in the controls, with decreased growth with increased ultrasound intensity. There was a significant reduction for feline herpesvirus with intensity, but there was no apparent effect of ultrasound on feline calicivirus. These results suggest that ultrasound in the low-kilohertz frequency range is capable to some degree of inactivating certain disease agents that may reside in water. The physical mechanism of inactivation appears to be transient cavitation.

Quantitative ultrasonic assessment of normal and ischaemic myocardium with an acoustic microscope: relationship to integrated backscatter

PURPOSE OF INVESTIGATION

The aim was to study ultrasonic propagation properties of normal and ischaemic myocardium with a scanning laser acoustic microscope and to correlate these changes with ultrasonic backscatter.

DESIGN

Myocardial ischaemia was produced by total occlusion of left anterior descending coronary artery in anaesthetised open chest dogs. Myocardium supplied by left circumflex coronary artery served as normal control. IBR5, an optimum weighted frequency average (4-6.8 MHz) of the squared envelope of diffraction corrected backscatter, was measured in vivo. Ultrasonic attenuation coefficient, an index of loss per unit distance, the propagation speed and heterogeneity index were measured from normal and ischaemic regions with a scanning laser acoustic microscope which operates at 100MHz in vitro. Myocardial water content of normal and ischaemic myocardium was also estimated.

SUBJECTS

Were five anaesthetised mongrel dogs.

RESULTS

Attenuation coefficient of 33.8(SD4.2) dB.mm-1 in the ischaemic tissue was lower than 63.8(17.2) dB.mm-1 in the normal tissue (p less than 0.01). Ultrasonic speed was lower in ischaemic than normal myocardium at 1584(25) v 1612(35) m.s-1 (p less than 0.05). Heterogeneity index of 11(7) m.s-1 in the ischaemic region was lower than 14(8) m.s-1 in the normal region (27% reduction, p less than 0.05). IBR5 and myocardial water content were higher in the ischaemic than the normal myocardium: -37.2(SEM1.8) dB v -46.6(0.6) dB, (p less than 0.01) and 80.9(0.0)% v 78(0.2)%, (p less than 0.05) respectively.

CONCLUSION

Ultrasonic properties of the myocardium are significantly altered during acute ischaemia.

Pulsed Doppler accuracy assessment due to frequency-dependent attenuation and Rayleigh scattering error sources

All engineering measurements are subject to inaccurate and imprecise estimates, including the estimate of blood flow velocity. An assessment of specific error sources can minimize such uncertainties. Frequency-dependent attenuation and Rayleigh scattering are significant error sources for pulsed Doppler ultrasound because the transmitted ultrasonic signal has a finite width spectrum. The former causes a frequency downshift and the latter a frequency upshift, both of which are independent of the actual Doppler frequency shift. This communication evaluates these error sources through computer stimulation and compares the computed error to experimental data.

Frequency dependence of tissue attenuation measured by acoustic microscopy

Broadband scanning acoustic microscopy (SAM) has been used to investigate the mechanical properties of sections of tissue with a resolution of around 8 microns. The work reported here extends these results by reporting the frequency dependence of the attenuation coefficient from 100-500 MHz. A discussion of the theory of the measurements is presented. The scanning laser acoustic microscope (SLAM) is used to characterize similar tissue sections at 100 MHz. The data obtained with the two forms of acoustic microscopy are compared with results from the literature.