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What we have learned from human studies
Abstracts Interventional procedures can be very challenging for everyone involved. A sonographer that has an interest in interventional ultrasound can be a valuable asset to the interventional team. Some departments overlook what a sonographer can offer and have very little if no sonographer involvement in procedures. Other departments let the sonographer be involved with the various physician groups that perform ultrasound-guided procedures. For example, in a radiology laboratory, the sonographer may work closely with the radiologists and alone with nephrologists in kidney biopsies. Sonographer involvement has many benefits. They can locate the pathology and determine various approaches, use their scanning skills to optimize the image to locate subtle lesions, use Doppler to ensure there are no vessels in the needle path, and be a second set of hands as needed. Their knowledge of new technologies such as tissue harmonics and compound imaging may facilitate the procedure. When using guides, the sonographer can hold the transducer freeing the physician’s hands. This can be helpful when aspiration techniques are used. Very importantly, the sonographer can communicate and watch the patient during the procedure. This can be valuable by helping patients control their breathing and giving them someone to talk to as needed. The sonographer can coach and support the patient emotionally allowing the physician to concentrate on the procedure or discuss the specimen with the cytopathologist, if present. Importantly, the sonographer can be a time saver to a busy physician. The sonographer can be scanning the patient while the physician signs up the next patient or checks and dictates other studies. With a sonographer involved, a second physician may not be required, thus allowing patient flow to continue, as well as assist in patient and probe preparation and clean up. In conclusion, the challenges offered with interventional procedures can keep a skilled sonographer from becoming bored. Every procedure and patient can be a different experience. A skilled sonographer can help busy physicians be more efficient with their time and be a very valuable member of the interventional team.
BIOEFFECTS AND SAFETY OF DIAGNOSTIC ULTRASOUND
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conclusions that can be drawn include: pulsed spectral Doppler ultrasound can produce biologically significant heating (⬎5°C) close to bone in the fetal brain and spinal column; the amount of ultrasoundinduced heating increases with gestational age and the development of fetal bone; the rate of heating near bone is rapid, with approximately 75% of the maximum heating occurring within 30 seconds; firsttrimester ultrasonic imaging poses very low risk of significant or adverse effects.
Bioeffects of ultrasound with contrast agents: In vitro Miller MW, Department of Obstetrics and Gynecology, University of Rochester, Rochester, NY Historical data are briefly reviewed to demonstrate the very large variability inherent in inter-trial replications of ultrasound (US)-induced hemolysis in vitro with or without the presence of echo contrast agents. Statistical analyses of such widespread data for specific comparative tests are undertaken and compared with those of “clinical titration procedures” in which “dose” is administered to achieve a specific effect from which additional testing procedures can then be undertaken for comparative assays. Use of this “titration procedure” is then applied to the testing of four hypotheses related to environmental and biological factors associated with US-induced hemolysis in vitro. For each hypothesis, anticoagulated whole human blood in vitro in the presence of a clinical concentration of an echo contrast agent (Albunex®) was used. The four hypotheses are that: 1) cell size is an important factor in US-induced hemolysis, the larger the cell the greater the hemolytic yield; 2) the antioxidant Trolox®, an analogue for Vitamin E, causes a “kink” in the bilipid membrane layer with resulting physical instability and hence increased potential for US-induced hemolysis; 3) the extent of gas content as reflected by the partial pressure of oxygen in the blood determines the extent of US-induced hemolysis, the higher the gas content the greater the US-induced hemolytic yield; and 4) temperature can affect the fragility of the cell membrane and lead to increased US-induced hemolysis. The results are related to the occurrence of US-induced inertial cavitation.
Ultrasound-induced temperature rise in fetal brain Barnett SB, Health Service Sector, CSIRO, Lindfield, NSW, Australia In 1992, the WFUMB Symposium on thermal bioeffects concluded that the threshold for irreversible brain damage in the developing embryo or fetus is exceeded in experimental situations when a temperature increase of 4°C is maintained for 5 minutes. It also concluded that exposure to pulsed spectral Doppler ultrasound can produce significant heating of biological tissue near bony tissue. In the decade since those conclusions, there has been a continuing increase in acoustic outputs of equipment operating in Doppler and in B-mode. This has significant thermal implications for sensitive fetal neural tissue close to bone, particularly in Doppler flow studies of fetal cerebral vessels. The skull bone, with its high acoustic absorption coefficient, is easily heated by the absorption of acoustic energy and this can potentially perturb the adjacent tissues of the cerebral cortex. Tissues of the central nervous system are sensitive to damage by physical agents including heat and ultrasound. Ultrasound users are encouraged to assess the risk/benefit ratio based on their interpretation of equipment output displays (including the thermal index, TI) and an understanding of the significance of biological effects. To assist in the assessment of potential thermally mediated bioeffects, this paper will present the status of scientific evidence on the extent of ultrasound-induced heating that may be produced in diagnostic applications and the potential biological consequences. For most applications, the risk is relatively low; however, there is good reason for caution and prudent use in obstetrics. Some
What we have learned from human studies Salvesen K, National Center for Fetal Medicine, Trondheim, Norway Epidemiological studies have indicated no associations between prenatal ultrasound and childhood cancer, dyslexia, poor school performance, delayed neurological development, poor vision, or hearing. However, a statistical significant association between prenatal ultrasound and sinistrality among males has been found in four epidemiological studies, and so far no other epidemiological evidence contradicts this association. The evidence will be discussed according to study design and statistical methods, and a possible causal relationship between prenatal ultrasound and left-handedness will be discussed according to the Bradford Hill’s criteria of causality. The conclusion is that although a statistically significant association has been found, there is not enough evidence to believe that there is a causal association. There is a need for further studies. Based on scientific epidemiological evidence of possible harmful effects of prenatal ultrasound, there is no reason to withhold scanning for any clinical application.
Bioeffects of ultrasound contrast agents in vivo Dalecki D, Biomedical Engineering, University of Rochester, Rochester, NY
BIOEFFECTS AND SAFETY OF DIAGNOSTIC ULTRASOUND
S79
conclusions that can be drawn include: pulsed spectral Doppler ultrasound can produce biologically significant heating (⬎5°C) close to bone in the fetal brain and spinal column; the amount of ultrasoundinduced heating increases with gestational age and the development of fetal bone; the rate of heating near bone is rapid, with approximately 75% of the maximum heating occurring within 30 seconds; firsttrimester ultrasonic imaging poses very low risk of significant or adverse effects.
Bioeffects of ultrasound with contrast agents: In vitro Miller MW, Department of Obstetrics and Gynecology, University of Rochester, Rochester, NY Historical data are briefly reviewed to demonstrate the very large variability inherent in inter-trial replications of ultrasound (US)-induced hemolysis in vitro with or without the presence of echo contrast agents. Statistical analyses of such widespread data for specific comparative tests are undertaken and compared with those of “clinical titration procedures” in which “dose” is administered to achieve a specific effect from which additional testing procedures can then be undertaken for comparative assays. Use of this “titration procedure” is then applied to the testing of four hypotheses related to environmental and biological factors associated with US-induced hemolysis in vitro. For each hypothesis, anticoagulated whole human blood in vitro in the presence of a clinical concentration of an echo contrast agent (Albunex®) was used. The four hypotheses are that: 1) cell size is an important factor in US-induced hemolysis, the larger the cell the greater the hemolytic yield; 2) the antioxidant Trolox®, an analogue for Vitamin E, causes a “kink” in the bilipid membrane layer with resulting physical instability and hence increased potential for US-induced hemolysis; 3) the extent of gas content as reflected by the partial pressure of oxygen in the blood determines the extent of US-induced hemolysis, the higher the gas content the greater the US-induced hemolytic yield; and 4) temperature can affect the fragility of the cell membrane and lead to increased US-induced hemolysis. The results are related to the occurrence of US-induced inertial cavitation.
Ultrasound-induced temperature rise in fetal brain Barnett SB, Health Service Sector, CSIRO, Lindfield, NSW, Australia In 1992, the WFUMB Symposium on thermal bioeffects concluded that the threshold for irreversible brain damage in the developing embryo or fetus is exceeded in experimental situations when a temperature increase of 4°C is maintained for 5 minutes. It also concluded that exposure to pulsed spectral Doppler ultrasound can produce significant heating of biological tissue near bony tissue. In the decade since those conclusions, there has been a continuing increase in acoustic outputs of equipment operating in Doppler and in B-mode. This has significant thermal implications for sensitive fetal neural tissue close to bone, particularly in Doppler flow studies of fetal cerebral vessels. The skull bone, with its high acoustic absorption coefficient, is easily heated by the absorption of acoustic energy and this can potentially perturb the adjacent tissues of the cerebral cortex. Tissues of the central nervous system are sensitive to damage by physical agents including heat and ultrasound. Ultrasound users are encouraged to assess the risk/benefit ratio based on their interpretation of equipment output displays (including the thermal index, TI) and an understanding of the significance of biological effects. To assist in the assessment of potential thermally mediated bioeffects, this paper will present the status of scientific evidence on the extent of ultrasound-induced heating that may be produced in diagnostic applications and the potential biological consequences. For most applications, the risk is relatively low; however, there is good reason for caution and prudent use in obstetrics. Some
What we have learned from human studies Salvesen K, National Center for Fetal Medicine, Trondheim, Norway Epidemiological studies have indicated no associations between prenatal ultrasound and childhood cancer, dyslexia, poor school performance, delayed neurological development, poor vision, or hearing. However, a statistical significant association between prenatal ultrasound and sinistrality among males has been found in four epidemiological studies, and so far no other epidemiological evidence contradicts this association. The evidence will be discussed according to study design and statistical methods, and a possible causal relationship between prenatal ultrasound and left-handedness will be discussed according to the Bradford Hill’s criteria of causality. The conclusion is that although a statistically significant association has been found, there is not enough evidence to believe that there is a causal association. There is a need for further studies. Based on scientific epidemiological evidence of possible harmful effects of prenatal ultrasound, there is no reason to withhold scanning for any clinical application.
Bioeffects of ultrasound contrast agents in vivo Dalecki D, Biomedical Engineering, University of Rochester, Rochester, NY