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.

Effects of in utero ultrasound exposure on the development of the fetal mouse testis

The effect on the developing fetal testis of in utero exposure to 1-MHz, continuous-wave ultrasound in the spatial peak, temporal average intensity range 0.5-10 W/cm2 for durations of 400-30 sec on Day 9, 12, or 15 of gestation was determined. Results show that two subtle, yet potentially deleterious, effects occurred: a reduction in the Sertoli cell population and an apparent delay in the cessation of gonocyte mitosis. An increase was also seen in the number of fetal resorptions and stillborn pups per number of implantation sites in the exposed specimens as compared to the sham and cage controls. Because the reduction in testis weight was proportional to decreased body weight and because there was no difference in Sertoli cell numbers due to day of treatment, the testicular effects may reflect a generalized delay in growth. Whether this effect of ultrasound on fetal testis will be translated into an equal reduction in germ cell numbers in the adult testis remains to be determined.

Legal liability in the use of ultrasound by office-based obstetricians

Ultrasound has proved to be a valuable diagnostic tool in the practice of obstetrics. Its rapidly increasing use by the office-based obstetrician, however, has opened a potential new area of legal vulnerability. The malpractice liability that may arise from its use is reviewed and practical ways to avoid it are considered.

The thermal dose index

OBJECTIVE

A new index is proposed to help sonographers easily assess the risk of an adverse thermal effect arising from a clinical examination. It is called the thermal dose index (TDI).

METHODS

The TDI uses the familiar thermal index (TI) and the examination duration to compute a dimensionless index.

RESULTS

The greater the TDI value, the greater the risk of a thermally induced adverse effect. If the TDI is 1 or less, there is no expectation of a thermally induced adverse effect.

CONCLUSIONS

Like the TI, the TDI would be a convenient index that is continually updated and displayed during an ultrasound examination. The TDI is a new estimate of thermal risk that takes into account the duration of an ultrasound examination.

Comparison of Thermal Safety Practice Guidelines for Diagnostic Ultrasound Exposures

This article examines the historical evolution of various practice guidelines designed to minimize the possibility of thermal injury during a diagnostic ultrasound examination, including those published by the American Institute of Ultrasound in Medicine, British Medical Ultrasound Society and Health Canada. The guidelines for prenatal/neonatal examinations are in general agreement, but significant differences were found for postnatal exposures. We propose sets of thermal index versus exposure time for these examination categories below which there is reasonable assurance that an examination can be conducted without risk of producing an adverse thermal effect under any scanning conditions. If it is necessary to exceed these guidelines, the occurrence of an adverse thermal event is still unlikely in most situations because of mitigating factors such as transducer movement and perfusion, but the general principle of "as low as reasonably achievable" should be followed. Some limitations of the biological effects studies underpinning the guidelines also are discussed briefly.

Vascular lesions and s-thrombomodulin concentrations from auricular arteries of rabbits infused with microbubble contrast agent and exposed to pulsed ultrasound

Arterial injury resulting from the interaction of contrast agent (CA) with ultrasound (US) was studied in rabbit auricular arteries and assessed by histopathologic evaluation and s-thrombomodulin concentrations. Three sites on each artery were exposed (2.8 MHz, 5-min exposure duration, 10-Hz pulse repetition frequency, 1.4-mus pulse duration) using one of three in situ peak rarefactional pressures (0.85, 3.9 or 9.5 MPa). Saline, saline/CA, and saline/US infusion groups (n = 28) did not have histopathologic damage. The saline/CA/US infusion group (n = 10) at exposure conditions below the FDA mechanical index limit of 1.9 did not have histopathologic damage, whereas the saline/CA/US infusion group (n = 9) at exposure conditions above the FDA limit did have damage (5 of 9 arteries). Lesions were characteristic of acute coagulative necrosis. Mean s-thrombomodulin concentrations, a marker for endothelial cell injury, were highest in rabbits exposed to US at 0.85 and 3.9 MPa, suggesting that vascular injury may be physiological and not accompanied by irreversible cellular injury.

Towards evidence based emergency medicine: best BETs from the Manchester Royal Infirmary. Using the ultrasound compression test for deep vein thrombosis will not precipitate a thromboembolic event

A short cut review was carried out to establish whether patients with deep vein thrombosis (DVT) are at risk of embolism during ultrasound compression testing. No papers were found that directly answered the clinical question. The clinical bottom line is that currently there is no evidence to suggest that compressing vessels in order to identify a DVT could cause an embolic event. Therefore we can consider ultrasound assessment a safe reliable investigation for the diagnosis of DVT with no evidence of causing harm.

[Hysterosonography]

Hysterosonography, which consists in the injection of some cc of saline in the uterine cavity during sonography, allows an exploration of the uterine cavity and of the endometrium. Accuracy of hysterosonography is similar to that of office hysteroscopy. Hysterosonography distinguishes normal cavities from pathologic ones, endometrial atrophy from mucosal anomalies, polyps from myomas. Conversely, endometrial biopsy is still necessary for diagnosis of hyperplasia or cancer. Hysterosonography can also be proposed for first trimester bleedings, trophoblast retention or ectopic pregnancy. In the near future it could be applied to therapeutic goals such as sonographic section of polyps.

On the mechanisms of ultrasound contrast agents-induced arrhythmias

Recent reports have shown that imaging hard-shelled ultrasound (US) contrast agents at high mechanical indices engenders premature ventricular contractions (PVCs). We have shown that the oscillations of microbubbles next to a cell induce a mechanical pressure on its membrane resulting in the activation of stretch activated channels (SAC). The aim of this study is to demonstrate, in vivo and in vitro, the relationship between PVCs and SAC opening. Five anesthetized rats were used. PVCs were created in vivo with (1) US and a diluted solution of contrast microbubbles injected intravenously through the tail vein at a rate of 0.5 mL per min and (2) a manually induced mechanical stimulus, which consisted of stimulations by a flexible catheter introduced into the rat aorta and pushed until the left ventricle. PVCs were quantified through ECG measurements. In vitro experiments consisted of patch Clamp measurements on HL-1 heart cell line. The stimulation was carried out either manually with a glass rod or with US and microbubbles. For both in vivo and in vitro experiments, US consisted of 40-cycle waveforms at 1 MHz and peak negative pressures up to 300 kPa and exposure time varied from 1 to 2 min. We should emphasize that these parameters are different from those used in diagnostic conditions. In vivo, microbubbles and US at 300 kPa induced modification of rat's ECG while pressures below 300 kPa did not induce any PVC. US alone did not modify the rat's ECG. Similar PVCs were also created when stimulation with a catheter was applied. Regular heart beat rate was recovered immediately after the stimulation was stopped. In vitro, the mechanical stretch induced a cell membrane depolarization due to SAC opening. Similar effect was observed with US and microbubbles. The cell potential returned to its initial value when the stimulation was released. In conclusion, we presume that PVCs are generated through a cascade of events characterized by a mechanical action of oscillating microbubbles, opening of stretch activated ion channels, membrane depolarization and triggering of action potentials.

Contrast-aided diagnostic ultrasound does not enhance lung metastasis in a mouse melanoma tumor model

OBJECTIVE

The purpose of this research was to test the hypothesis that contrast-aided diagnostic ultrasound (CADUS) could exacerbate the metastatic spread of mouse melanoma tumor cells to the lungs.

METHODS

The melanoma cell lines B16 and B16-D5 (metastatic specifically to lung) were implanted on a hind leg of female C57/bl6 mice. Growing tumors were scanned by 1.5-MHz diagnostic ultrasound in a 37 degrees C water bath. Four hundred image frames were triggered at a 1-Hz rate with 4 retro-orbital injections of an ultrasonographic contrast agent at dosage of 10 microL/kg at 100-second intervals. Sham-treated mice received 400 frames of ultrasonography followed by the contrast agent with the ultrasound off. The primary tumor was surgically removed 1 day after ultrasound administration. Lungs were removed and evaluated blind after 2 weeks of bleaching in Fekete solution.

RESULTS

Three experiments were performed. The first experiment involved scanning sham and CADUS groups of 20 mice each with B16 tumors; B16 metastasis was not enhanced. The second experiment repeated this test with the D5 cell line; the metastasis enhancement was marginally significant for average number (0.3 and 3.2; P = .06) and incidence (3 and 9 of 19; P = .08) in mice without tumor recurrence. Finally, a third experiment was performed to clarify ambiguous results in the second experiment and consisted of 2 groups of 40 mice each. In this larger experiment, the results were essentially equal for the sham and CADUS groups.

CONCLUSIONS

Overall, the results do not support the hypothesis of CADUS-enhanced metastasis.

Progress in medical ultrasound exposimetry

Biomedical applications of ultrasound have experienced tremendous growth over the past 50 years. Early work in thermal therapy and surgery soon was followed by diagnostic imaging and Doppler. Because patient safety was an important issue from the beginning, the study of methods for measuring exposure levels, and their relationship to possible biological effects, paralleled the growth of the various therapeutic and diagnostic techniques. The diverse conditions of use have presented a range of exposure measurement challenges, and the sensors and techniques used to evaluate ultrasound fields have had to evolve as new or expanded clinical applications have emerged. In this paper some of the more notable of these developments are presented and discussed. Topics covered include devices and techniques, methods of calibration, progress in standardization, and current problem areas, including the effects of nonlinear propagation. Some early methods are described, but emphasis is given to more recent work applicable to present and future uses of ultrasound in medicine and biology.

A series of 3 cases of corneal abrasion with multiple etiologies

BACKGROUND

Most corneal abrasions are caused by mechanical injuries affecting the superficial epithelial layer. Although one of the functions of the eyelid is to protect the eye, its reaction time of about 425 msec is slower than many ocular insults; thus, corneal abrasions are among the most commonly occurring eye emergencies.

CASE REPORTS

Three cases of corneal abrasions with different etiologies are presented. The first case was a large abrasion of the cornea near the visual axis caused by a wood chip. A metal foreign body with rust was lodged in the cornea from metal grinding in the second case. The third case was iatrongenically induced by an A-scan probe while a fellow student was measuring the axial length of the eye.

CONCLUSION

Corneal abrasions are one of the most common ocular conditions presented to eye clinics or emergency departments. Although there are different etiologies of abraded corneal epithelium, current clinical management for most corneal abrasions involves a bandage contact lens, use of topical antibiotics, and cycloplegics. Large and central corneal abrasions, however, warrant a consultation with a corneal specialist.

Use of intraoperative intracavitary (direct-contact) ultrasound for resection control in transsphenoidal surgery for pituitary tumors: evaluation of a microsurgical series

BACKGROUND

Perisellar infiltration may be responsible for incomplete removal of pituitary tumors. Since intraoperative visualization of parasellar structures is difficult during transsphenoidal surgery, we are describing the use of intraoperative direct contact ultrasound (IOUS).

METHODS

Within 5 years, in 113 transsphenoidal operations (58 male, 55 female, age 14-81 years, 110 pituitary adenomas (mean diameter 26.6 mm, 69 non-secreting adenomas, 41 secreting adenomas), and 1 of each Rathke's cleft cyst, craniopharyngioma, and xanthogranuloma), IOUS was applied. After wide opening of the sellar floor and removal of the intrasellar tumor portions, a commercially available side fire ultrasound probe is introduced, and in direct contact to the sellar envelope, the perisellar space is scanned perpendicular to the axis of the working channel. We compared the results of IOUS to postoperative MRI after 3-6 months.

RESULTS

Identification of the intracavernous ICA, the anterior optic pathway, and the ACA, was possible, it was safe to operate close to them. In 65 operations (58%), further resection of tumor remnants was performed after IOUS. In this selected series, complete resection of tumors (stated by postoperative MRI after 3-6 months) was achieved in 75 operations (66%) and remission was achieved in 18 operations of secreting adenomas (44%). Compared to MRI after 3 to 6 months, the sensitivity of IOUS was 0.568 and the specificity was 0.907. No complications related to IOUS were seen.

CONCLUSIONS

Visualization of the perisellar compartments by IOUS is easy and fast to perform. It allows the surgeon to identify resectable tumor remnants intraoperatively, which otherwise could be missed.

Contact dermatitis after ultrasonography and electrocardiography

We report 4 patients who developed allergic contact dermatitis after ultrasound investigations. Patch testing was positive with conducting gels, and in 2 cases with propylene glycol. Contact dermatitis to gels is also seen in electrographic practice and after transcutaneous electrical analgesia.

Ultrasound in obstetrics: do the published evaluative studies justify its routine use?

A review of surveys assessing the use of ultrasound in obstetrics was undertaken to determine why this examination has spread so rapidly. Seven randomized controlled trials (RCTs) published to date as well as 182 papers published in four obstetric journals between 1979 and 1984 were reviewed. The value of routine ultrasound scanning to improve the diagnosis of intrauterine growth retardation or gestational age was demonstrated in the RCTs, but the results of the RCTs measuring the effects on health of this screening procedure did not give strong evidence for its routine use. Of the 182 papers identified, 137 were related to the diagnostic assessment of ultrasound, 14 concerned the effects on medical practice and only nine papers studied the effects of ultrasound scanning on health. Most of these 137 papers came out in favour of this procedure. Thus the spread of ultrasound scanning was based mainly on evaluative surveys which assessed its diagnostic value.

A comparison of hemolytic and sonochemical activity of ultrasonic cavitation in a rotating tube

Biological effects of in vitro ultrasonic exposure may result from mechanical and from sonochemical mechanisms related to ultrasonic cavitation. Mechanical cell lysis by 1.61 MHz ultrasonic cavitation was assessed in a rotating tube exposure system by hemolysis measurements. Free radical generation was assessed by the terephthalic acid dosimeter, calibrated by gamma-ray dosage. Sonochemical production was assessed by measuring residual hydrogen peroxide using the sensitive isoluminol method. Exposure conditions were similar for all tests, except longer durations were needed for the free radical and hydrogen peroxide tests. The sonochemical mechanisms were relatively more important for increasing intensity, and increasing temperature. Increasing rotation speed or bubbling with argon before exposure enhanced all cavitation activity. Stopping the rotation reduced all cavitation activity. Burst-mode ultrasound (10.5 microseconds bursts, 1:1 or 1:3 duty cycle) reduced cavitation activity, but gave relatively greater sonochemical activity under some conditions. These results indicate that the mechanical and sonochemical mechanisms can be separately favored to some extent by varying exposure conditions. The observed trends should be helpful for selecting exposure conditions favorable for studying bioeffects of the sonochemical mechanism.

Water intoxication: a complication of pelvic US in a patient with syndrome of inappropriate antidiuretic hormone secretion

A woman was first seen with water intoxication caused by the voluntary ingestion of water in an attempt to fill her bladder before undergoing pelvic ultrasound (US). As in two other reported cases, this woman was receiving medication that causes the syndrome of inappropriate antidiuretic hormone secretion. A patient undergoing transabdominal pelvic US who is receiving these medications and whose bladder is not full should undergo examination by means of a transvaginal or endorectal route.