The role of duplex carotid sonography, digital subtraction angiography, and arteriography in the evaluation of transient ischemic attack and the asymptomatic carotid bruit

This article reviews the uses of arteriography, venous digital subtraction angiography, and duplex carotid sonography in the evaluation of patients with an asymptomatic carotid bruit or carotid system transient ischemic attack. It concludes with a description of the authors' guidelines for their use.

Induction of sister-chromatid exchanges in human lymphocytes exposed in vitro and in vivo to therapeutic ultrasound

The induction of sister-chromatid exchanges (SCEs), chromosomal aberrations and cell-cycle delay was determined in human lymphocytes after treatment in vitro and in vivo with therapeutic ultrasound (u.s.). In vitro treatments (1 W/cm2; 0.860 MHz; for 40-160 sec) were performed on unstimulated lymphocytes from 9 donors: a statistically significant, dose-dependent increase in SCE frequency was produced, whereas no induction of chromosomal aberrations nor alteration of the distribution of 1st, 2nd and 3rd division metaphases were observed. The same increase in the frequency of SCEs was detected by treating in vitro stimulated lymphocytes with u.s. The effects of in vivo exposure to u.s. were detected on lymphocytes from 10 patients before, during and after u.s. therapy (0.6-1.0 W/cm2; 0.860 MHz; from 8 to 20 applications lasting 5-6 min each). SCE frequency was statistically significantly increased in all patients at mid-therapy, without a further increase during the second half of therapeutic cycle, and was restored to pretreatment level 3 months after the end of u.s. therapy. No increase in chromosomal aberrations was noticed during and after u.s. therapy, whereas erratic delays of the cell cycle were observed, not clearly related to u.s. application or SCE levels. A linear relationship was found between SCE frequency and age in 21 healthy donors.

Development of health risk evaluation data for diagnostic ultrasound: a historical perspective

The growth of ultrasound applications in diagnostic medicine has helped stimulate related biological effects investigations. Current data related to effects associated with diagnostic ultrasound indicate the need for additional research on cell surface structures, motility and developmental effects. Research on biological effects, especially for evaluating in vivo end points analogous to those employed by investigators using in vitro systems and simple organisms, are needed. Particular emphasis relative to potential effects on fetal and embroyonic development is indicated. Limited data also suggest the need to investigate possible effects on the immune response. There is a growing realization of the potential importance of nonthermal effects and increasing evidence that the temporal peak intensity is potentially related to the production of some effects. A number of recent comprehensive reviews have helped identify, analyze and evaluate some of the relevant data.

The effects of ionizing radiation, microwaves, and ultrasound on the developing embryo: clinical interpretations and applications of the data

The term "radiation" evokes emotional responses both from lay individuals and from professionals. Many spokespersons are unfamiliar with radiation biology or the quantitative nature of the risks. Frequently, microwave, ultrasound, and ionizing radiation risks are confused. Although it is impossible to prove no risk for any environmental hazard, it appears that exposure to microwave radiation below the maximal permissible levels present no measurable risk to the embryo. Ultrasound exposure from diagnostic ultrasonographic imaging equipment also is quite innocuous. It is true that continued surveillance and research into potential risks of these low-level exposures should continue, but at present ultrasound not only improves obstetric care but also reduces the necessity of diagnostic x-ray procedure. In the field of ionizing radiation, we have as good a comprehension of the biologic effects and the quantitative maximum risks as of any other environmental hazard. Although the animal and human data support the conclusion that no increases in the incidence of gross congenital malformations, intrauterine growth retardation, or abortion will occur with exposures below 5 rad, that does not mean that there are definitely no risks to the embryo exposed to lower doses of radiation. Whether there exists a linear or exponential dose-response relationship or a threshold exposure for genetic, carcinogenic, cell-depleting, and life-shortening effects has not been determined. In establishing maximum permissible levels for the embryo at low exposures, we use the information in Tables 2, 3, 4, 7, 10, and 14. It is obvious that the risks of 1-rad or 5-rad acute exposure are far below the spontaneous risks of the developing embryo, since 15% of human embryos abort, 2.7%-3.0% of human embryos have major malformations, 4% have intrauterine growth retardation, and 8%-10% have early- or late-onset genetic disease. The maximum risk attributed to a 1-rad exposure, approximately 0.003%, is thousands of times smaller than the spontaneous risks of malformations, abortion, or genetic disease (see Table 10). Thus, the present maximum permissible occupational exposures of 0.5 rem for pregnant women and 5 rem for medical exposure are extremely conservative. Medically indicated diagnostic roentgenograms are appropriate for pregnant women, and there is no medical justification for terminating a pregnancy in women exposed to 5 rad or less because of a radiation exposure.(ABSTRACT TRUNCATED AT 400 WORDS)

Sister chromatid exchanges in human lymphocytes after exposure to pulse-wave ultrasound

We have investigated the frequencies of sister chromatid exchange (SCE) induced by pulse-wave ultrasound in lymphocytes obtained from the human umbilical vein. The following results were obtained: There is an increase in the frequency of SCEs with increases in acoustic power. The critical acoustic power was 37.3-73 mW/cm2 (spatial average temporal average, SATA). Regardless of changes in pulse duration and repeated pulse frequency, if the acoustic power remains constant, the SCE frequency does not change significantly.

Investigation into the possible genetic effects of diagnostic ultrasound

The mutagenic effect of DUS (diagnostic ultrasound) was examined using two generators emitting continuous waves and pulsed waves, respectively. Three different test systems for mutagenic activity were employed in this study. 1. The frequency of sister chromatid exchanges (SCEs) was determined in metaphase chromosomes of human lymphocytes and of Chinese hamster ovary (CHO) cells sonicated at different stages of the cell cycle. 2. The induction of DNA single strand breaks was tested in CHO cells treated with continuous wave ultrasound. Following sonication an endonuclease was introduced into the cells converting single strand breaks to chromosomal aberrations scorable in the following metaphase. 3. The influence of DUS on the number of point mutations was evaluated in the Ames test. A tester strain of Salmonella typhimurium indicating base substitutions was sonicated. At the present stage, all results proved to be completely negative and could thus not support the view of any mutagenic activity of diagnostic ultrasound.

Cellular inactivation by ultrasound

The lethal effect of ultrasound (US) on mammalian cells has received relatively little attention. Understandably, potential genetic aspects of US have been of prime concern to physicians who use US as a diagnostic tool; at the average power densities involved (<<1 W cm(-2)) little, if any cell killing is to be expected. There have been sporadic attempts to use higher intensities ( approximately 1 W cm(-2)) as a treatment modality in cancer therapy, but those experiments seem to have been based on inadequate cellular studies. The effects of US usually were evaluated in terms of morphological criteria rather than on quantitative determination of the loss of viability as measured by colony formation. There are few reports of the effects of US on survival of mammalian cells, and none specifically examine hyperthermic interaction. With the increased interest in hyperthermia for tumour therapy, attention has been directed towards the use of ultrasound to achieve tumour heating. In preliminary experiments in which US was used to heat the EMT6 sarcoma and KHJJ carcinoma in mice, we found a high percentage of tumour cures with short (approximately 30 min) treatments at temperatures (43-44 degrees C) where in vitro results of hyperthermia-induced cell killing would not have led to a prediction of any cures. We therefore initiated an investigation of the effects of US on survival of Chinese hamster cells to see if direct cell killing by US could explain our in vivo results, or, as in the case of radiofrequency (RF) electromagnetic heating, we would be forced to invoke host response(8). In particular, we examined the thermal and non-thermal components of cellular inactivation by US. We report here that there is a definite non-thermal cytotoxic effect of US. Its relative contribution to cell killing is a highly nonlinear function of the temperature of the cellular milieu. The survival curves show clearly that, beyond an initial threshold, small changes in temperature and/or US intensity can give rise to impressive changes in survival values. The threshold nature of the data strongly suggests that by means of overlapping beams, ultrasound energy could be delivered to tumour tissue to achieve massive cell killings while sparing normal tissue outside the tumour volume to a degree far exceeding that of conventional techniques.