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US e GestacaoFrom: Maria Helena (mhbastos@uol.com.br)Fri, 13 Sep 2002 20:04:27 -0300
Advance for Imaging and Radiation Therapy Professionals January 28, 2002 Loud as a Speeding Train? Study finds that ultrasound produces vibrartions that may 'sound' as loud as a subway train to the fetus Ultrasound scans are audible to a fetus, researchers reported at the Dec. 3, 2001, meeting of the Acoustical Society of America in Fort Lauderdale, Fla. Moreover, when the ultrasound probe is pointed in the right direction, the ultrasound pulse may produce vibrations as intense as a train coming into a station, said Mostafa Fatemi, PhD, associate consultant in the Ultrasound Research Laboratory, Department of Biophysics at the Mayo Foundation in Rochester, Minn., lead author of the study. If ultrasound is defined as sound that lies beyond the range of human hearing, how can a fetus hear an ultrasound scan? "This is really a secondary effect," explained Dr. Fatemi. "Ultrasound is not audible, but, the ultrasound energy produces a tapping force on any organ or object that it intercepts. "When that tapping force is repeated, it produces a vibration similar to that produced by sound. As the ultrasound beam moves during examination of the fetus, the focal point of the beam can pass over the fetal head. When this happens, the sensitive hearing structure of the fetus receives vibrations at a rate equal to the number of pulses per second from the ultrasound beam. The radiation force of these vibrations produces a localized "noise" that might range from 85 decibels to 120 decibels if it were traveling through air. This is equivalent to the level of sound produced by an approaching subway train. However, because sound is focused on a tiny, square-millimeter spot, and the sound diminishes rapidly from that spot, the fetus could quickly adjust its position to avoid the loudness. To measure the pressure produced on the hearing mechanism of the fetus by the acoustic emanations, the researchers measured the intensity of the radiation force of the ultrasound probe in water baths and in the human body. "Knowing the intensity, we know how much force and pressure it will produce at a localized point," said Dr. Fatemi. "The 85-120 decibel equivalent force is a typical value that varies from machine to machine and setting to setting." Unlike sound, however, this force is confined to a very sharp focal area and even a 1-centimeter change in focus significantly reduces the acoustic vibrations "heard" by the fetus, he noted. The purpose of the study was to explain the physical principle behind the observation from physicians and sonographers that the fetus moves more than usual in the uterus during an ultrasound exam, said Dr. Fatemi. While the study shows that the acoustic stimulation is probably the cause of this increased movement, he stressed that the question of whether the ultrasound vibrations cause any harm to the fetus was not a subject of this project -By Joyce Ward, CNMI, RT(N) [As partes desta mensagem que não continham texto foram removidas] Para enviar uma mensagem aos membros da lista, escreva para: partonatural@eGroups.com Para cancelar a sua assinatura na lista, basta enviar uma mensagem em branco para: partonatural-unsubscribe@eGroups.com Todas as mensagens já enviadas estão disponíveis no endereço: http://br.egroups.com/group/partonatural Qualquer problema, dúvida ou reclamação, por favor, envie um e-mail para o administrador: partonatural-owner@egroups.com Seu uso do Yahoo! Grupos é sujeito às regras descritas em: http://br.yahoo.com/info/utos.html
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