Endoscopic ultrasonography

Endoscopic ultrasonography (ES) enables accurate imaging of the layering structures of the gastrointestinal tract. The equipment is still evolving but has already reached a high degree of sophistication. The most relevant clinical indications are the analysis of submucosal tumors, the imaging of intestinal vascular anomalies, and, especially, the staging of gastrointestinal and biliopancreatic malignancy and the monitoring of the therapeutic efficacy of surgery, Nd:Yag laser photodestruction, and radiotherapy.

Ultrasonic heating of lung tissue

Tests with mice show that lung tissue is not selectively heated in comparison with other soft tissues and that lung has an efficient mechanism for dissipating that heat which is produced. Temperatures measured with a fine thermocouple placed at the outer surface of the mouse lung show approximately 1 degree C total rise in temperature in the living animal for an incident intensity of 1 W/cm2 (4 MHz, unfocused sound field).

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.

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.

Medical sonography: reproductive effects and risks

While it is clear that the levels and types of medical sonography that have been used in the past have no measurable risks, it would be inaccurate to label the modality of ultrasound as totally safe regardless of exposure. Most agents have reproductive risks and even teratogenic risks if the exposure is raised sufficiently. Thus the prudent use of sonography means that clinicians and designers of equipment have to maintain exposures far below the risks that have been demonstrated in animal studies and from the knowledge obtained about the physical changes that can be produced in humans as the absorbed dose is elevated. The reproductive risks were evaluated using five criteria: 1) human epidemiology, 2) secular trend data, 3) animal experiments, 4) dose response relationships, and 5) biologic plausibility. The analysis reveals that the human epidemiology does not indicate that diagnostic ultrasound presents a measurable risk to the developing embryo or fetus. Animal studies also indicate that diagnostic levels of ultrasound are safe and do not elevate the fetal temperature into the region where deleterious embryonic and fetal effects will occur. Because higher exposures of ultrasound can elevate the temperature of the embryo, the use of diagnostic procedures and the design of sonographic equipment should take into consideration the hyperthermic potential of higher exposures of ultrasound and the hypothetical additional risk of performing sonography on pregnant patients who are febrile. It would appear that if the embryonic temperature never exceeds 39 degrees C, then there is no measurable risk. We suggest that sonography (the field) and sonogram (the procedure) are the most appropriate and least anxiety provoking terms.

The effects of the microbubble suspension SH U 454 (Echovist) on ultrasound-induced cell lysis in a rotating tube exposure system

Human erythrocytes resuspended at different hematocrits in autologous plasma at 37 degrees C were exposed to the therapeutic intensities of continuous-wave 0.75-MHz ultrasound in vitro in a rotating tube exposure apparatus designed to maximize the destructive effects of cavitational activity. Provided that large numbers of additional gas bubbles had not been introduced during the various preparative and manipulatory procedures, the addition of Echovist at final concentrations comparable with those currently being used for clinical investigations resulted in a statistically significant increase in the amount of cell lysis in vitro in those samples having hematocrits less than 2%. The amount of cell lysis produced at any given ultrasound intensity decreased with increasing hematocrit in both the controls and the cell suspensions containing Echovist until it was virtually zero in both cases at hematocrits of 5.5% or greater. The addition of Echovist to samples that already contained large numbers of stabilized gas bubbles and/or had hematocrits greater than 5.5% produced no detectable cell lysis even at ultrasonic intensities as high as 3 W/cm 2 spatial average, temporal average (SATA). It is therefore unlikely that Echovist would cause appreciable amounts of cell lysis when the gas bubbles were being exposed to ultrasound under the conditions used for clinical investigations in vivo.

Thresholds for transient cavitation produced by pulsed ultrasound in a controlled nuclei environment

Transient cavitation is a discrete phenomenon that relies on the existence of stabilized nuclei, or pockets of gas within a host fluid, for its genesis. A convenient descriptor for assessing the likelihood of transient cavitation is the threshold pressure, or the minimum acoustic pressure necessary to initiate bubble growth and subsequent collapse. An automated experimental apparatus has been developed to determine thresholds for cavitation produced in a fluid by short tone bursts of ultrasound at 0.76, 0.99, and 2.30 MHz. A fluid jet was used to convect potential cavitation nuclei through the focal region of the insonifying transducer. Potential nuclei tested include 1-microns polystyrene spheres, microbubbles in the 1- to 10-microns range that are stabilized with human serum albumin, and whole blood constituents. Cavitation was detected by a passive acoustical technique that is sensitive to sound scattered from cavitation bubbles. Measurements of the transient cavitation threshold in water, in a fluid of higher viscosity, and in diluted whole blood are presented. These experimental measurements of cavitation thresholds elucidate the importance of ultrasound, host fluid, and nuclei parameters in determining these thresholds. These results are interpreted in the context of an approximate analytical theory for the prediction of the onset of cavitation.

Effects of pulsed ultrasound and temperature on the development of rat embryos in culture

Rat embryos in culture were exposed to pulsed ultrasound at SPTA intensity of 1.2 W/cm2 for 5, 15, and 30 min on day 9.5 of development. The whole embryo culture system allowed precise temperature control for directly examining the effects of ultrasound on the developing neural plate. After exposure, embryos were maintained in culture for a further 48 hr. No major morphological abnormalities were observed but a reduction in somite number occurred in the group insonated for 30 min, which was equivalent to a 2 hr delay in embryonic development. Similar delay in growth and "blistering" in the prosencephalon region of some embryos were observed after insonation for 15 min at 40.0 degrees C, an elevation of 1.5 degrees C over the temperature used for controls. Exposure to ultrasound for 15 min at 40 degrees C caused significant reduction in the growth of the head compared with that of control embryos. Heat shock genes for hsps 71/73 and 88 kD were induced after insonation for 30 min at 38.5 degrees C. Insonation did not cause any temperature changes in the culture medium. However, when the temperature of the culture medium was increased during insonation, defective development occurred. The results of these in vitro experiments suggest that ultrasound if resulting in significant hyperthermia could affect the development during early organogenesis of the neural plate and in particular they suggest that the embryo is at greater risk of damage during hyperthermic conditions. These results should provoke discussion of the concept that ultrasound in the febrile patient may present an increased embryonic risk which should be considered when deliberating on the use of diagnostic ultrasound procedures in the pregnant patient.

Does pulsed-Doppler ultrasound have mutagenic effects? Application of the Ames mutagenicity assay to test pulsed-Doppler equipment

Measurement of fetal blood flow has been accepted using pulsed-Doppler ultrasound. Until recently, there has been a lack of investigations concerning the potential risks of this method. The possible mutagenic effect of a pulsed-Doppler system was examined in vitro by applying the Ames test. Tester strains of Salmonella typhimurium indicating point mutations were irradiated (TA 98, TA 100, TA 102, TA 1535, TA 1537, TA 1538). A commercially available duplex system was applied in the experiments emitting an ultrasound beam with a spatial-peak temporal-average of 5.2 mW/cm2 and a spatial-peak temporal-peak of 117 mW/cm2 at a frequency of 2 MHz. The tester strains were sonicated up to 60 minutes, the bacterial suspension being in direct contact with the transducer surface. The ultrasound-exposed bacterial suspensions were compared with nonexposed samples. Reference mutagens were used for checking the sensitivity of the system. The results do not indicate any mutagenic effects.

The safety of obstetric ultrasonography: concern for the fetus

It has been estimated that more than half of all pregnant women in the United States undergo diagnostic ultrasound during their pregnancies. In light of this, the question of safety is of fundamental importance. Nondiagnostic ultrasound has been shown to produce biologic effects by thermal and cavitational activities. However, diagnostic ultrasound uses much lower intensities, and no evidence exists to suggest that it is associated with adverse effects. Numerous studies have examined the biologic effects of diagnostic ultrasound in insects, plants, cell suspensions, and even small mammals. The data from these experiments are confusing when attempting to relate these findings to the human. Epidemiologic data in humans, used to evaluate the potential adverse effects of exposure to diagnostic ultrasound, have revealed no ill effects from such exposure. Current data indicate that there are no confirmed biologic effects on patients and their fetuses from the use of diagnostic ultrasound and that the benefits to patients exposed to prudent use of diagnostic ultrasound outweigh the risks, if any. This review discusses the available information on the safety of obstetric ultrasonography.

Catheter-based intravascular ultrasound discriminates bicuspid from tricuspid valves in adults with calcific aortic stenosis

A catheter-based intravascular ultrasound transducer was used to study aortic valve morphology in adults with calcific aortic stenosis. Examination of 14 postmortem specimens disclosed that intravascular ultrasound consistently identified the number of cusps or the presence of a calcified median raphe in the conjoined cusp, or both, and thereby distinguished a calcified bicuspid from a calcified tricuspid aortic valve. These postmortem findings were then employed to identify valvular morphology in 15 patients undergoing diagnostic cardiac catheterization or balloon aortic valvuloplasty, or both. Reproduction of criteria established in vitro allowed discrimination of congenital valvular morphology in all 15 patients, including 7 in whom assessment by intravascular ultrasound was confirmed by subsequent pathologic examination. Identification of aortic valvular morphology by intravascular ultrasound has potential therapeutic implications for patients considered to be candidates for operative or nonoperative aortic valvuloplasty.

Effects of ultrasound on DNA and RNA synthesis in preimplantation mouse embryos

Ultrasound is used extensively to monitor the growth of ovarian follicles in in vitro fertilization and embryo transfer (IVF-ET) programs, as well as to follow the progress of early pregnancy. There have been scattered reports in the literature that exposure to ultrasound may have an adverse effect on reproduction in the rat (Bologne et al: CR Soc Biol 177:381-387, 1983; Demoulin et al: Ann NY Acad Sci 442:146-152, 1985), and also in humans (Demoulin et al: Ann NY Acad Sci 442: 146-152, 1985). We report here that diagnostic levels of pulsed ultrasound did not affect either the number of embryos produced, or the ability to incorporate labelled precursors into DNA and RNA, respectively. Measurements of temperature elevation of ovaries exposed to ultrasound showed that neither controls nor experimental tissue exhibited temperature elevation greater than 1 degree C.

Sister chromatid exchanges in first-trimester chorionic villi after in vivo and in vitro exposure to diagnostic ultrasound

A study was done to evaluate the effects of diagnostic ultrasound on sister chromatid exchange (SCE) in first-trimester chorionic villi under controlled technical conditions. Chromosome analysis was performed by the direct method using spontaneous mitoses from the cytotrophoblast layer, and SCE visualization was accomplished by a 72 h treatment with 5-bromodeoxyuridine (BrdU) at a concentration of 10 micrograms/ml. The slides were stained with acridine orange. Immediately before first-trimester chorionic villus sampling, a group of ten pregnant women was exposed to diagnostic ultrasound for 20 min (in vivo exposure). This group of patients was compared with a control group who were not exposed. A mean value of SCE/cell frequency of 4.2 +/- 0.2 was found in the exposed pregnancies, while a value of 3.7 +/- 0.2 was observed in the control group. After in vitro exposure of chorionic villi obtained from elective abortions, the frequency of SCE/cell did not differ significantly among samples with different exposures (1, 2, and 3 h) and controls. The positive control (mitomycin C) yielded a significant increase in SCE frequency.

Endoscopic ultrasonography in the evaluation of colon and rectal disease

Endosonography of the colon has until recently been limited to examination of the rectum. Rigid and flexible instruments are currently available which allow for detailed images of the rectal wall. Comparative studies suggest that endosonography may be more accurate than computed tomography in the preoperative staging of rectal carcinoma. Recently, an ultrasound colonoscope has been developed which allows for visual examination, biopsy, and endosonography throughout the colon. Experience with this technique is limited and its role in the evaluation of colonic disease has not yet been determined. Further comparative trials are needed to more fully define the role of endosonography in the diagnosis of colorectal disease.

Effect of ultrasound monitoring of follicular growth on the conception rate. A clinical study

Periovulatory ultrasonography (POUS) was performed on 59 anovulatory women over 523 treatment cycles. Follicular development was stimulated with either clomiphene citrate (CC) or human menopausal gonadotropin (hMG). Thirty-one pregnancies were induced; 23 went to term. Three factors were considered in evaluating the incidence of conception: the patient's age, drug use and the presence or absence of POUS. There was no evidence that the pregnancy rate after POUS differed from that without it (estimated conception rate ratio = 1.2:1, P = .76). Similarly, conceptus viability was not demonstrably different whether POUS was used or not (P = 1.00). However, the data show a strong advantage of hMG over CC in achieving conception (estimated conception rate ratio = 5.85, P less than .0001) and no disadvantage in conceptus viability (P = 1.00). The data also suggest that in women less than 30 years of age with polycystic ovaries, ovulation induction is easier to achieve and the conception rate higher than in older women. There was no evidence that POUS decreased the conception rate or increased fetal wastage.

The significance of membrane changes in the safe and effective use of therapeutic and diagnostic ultrasound

The cellular changes, such as alterations in motility and the stimulation of synthesis and secretion, induced by relatively low intensities of therapeutic ultrasound (e.g. 500 mW cm-2, SAPA; 100 mW cm-2 SATA) are primarily non-thermal in origin. They appear to be associated with changes in the permeability of the cell (plasma) membrane and in the transport of ions and molecules across it, effects which have been demonstrated in cells irradiated in suspension. In epithelial tissues, both in vitro and in vivo, it has been demonstrated that not only the cellular membrane transport pathways but also the paracellular or intercellular pathways are affected. Although membrane-mediated effects can be of value therapeutically, they could produce adverse effects if they were to occur during development, for the reception and transmission by the membrane of environmental signals are involved in determination of the fate of each cell. Determination is followed by selective gene expression and differentiation, that is, by the progressive increase in structural complexity brought about by the acquisition of specialised characteristics by various cell groups. Most cells of early embryos are ionically coupled via gap junctions which provide an intercellular pathway for electrochemical signalling and the maintenance of the concentration gradients which provide the cells with positional information. Differentiation of the cells varies according to their location with respect to these gradients. Increase in the intracellular concentration of calcium ions, which has been shown to occur after exposure to therapeutic levels of ultrasound, can decrease the permeability of gap junctions and uncouple cells, in the manner which occurs when they differentiate. Ultrasonically induced increases in calcium ion concentration are thus of considerable clinical significance, since they could affect differentiation and consequently histogenesis. Modification of plasma membrane permeability and transport properties, resulting in changes in the availability and activity of second messengers such as free calcium ions, can have profound effects on cell behaviour. Calcium channels appear to be the first channels to develop in the cell membranes of embryos, and internal calcium ion concentration is known to affect the synthesis of fetal proteins. Although generally reversible at intensities of less than 500 mW cm-2, changes in membrane permeability, particularly to calcium ions, could, if prolonged, have undesirable side effects not only on embryogenesis but on late prenatal and postnatal development. It is therefore recommended that the environmental conditions, thresholds, and mechanisms involved in the production of such changes be determined, so that they can be avoided when ultrasound is used diagnostically on sensitive targets such as embryos and fetuses.

Complications of ultrasonically guided fine-needle abdominal biopsy. Results of a multicenter Italian study and review of the literature. The Cooperative Italian Study Group

This report describes the complications following 10,766 ultrasonically guided fine-needle biopsies performed from 1979 to 1987 in 33 Italian echographic units. The mortality was 0.018%: the two reported deaths were due to hemoperitoneum and occurred in patients with hepatocellular carcinoma arising in a cirrhotic liver. Twenty patients (0.18%) had major complications. This series confirms that abdominal biopsy with fine needles is safe, even though our death rate was higher than in previous reports. Among the other nine fatalities following fine-needle abdominal biopsy reported in the literature, seven were secondary to hemorrhage. The biopsy of pancreatic carcinoma was more dangerous for needle-tract seeding (five of eight reported cases, including one in our series).