Alteração da temperatura nos tecidos biológicos com a aplicação do ultrassom terapêutico: uma revisão

INTRODUÇÃO: O ultrassom (US) terapêutico atua nos tecidos biológicos por meio da vibração, que é capaz de produzir efeitos fisiológicos térmicos e não térmicos. OBJETIVO: Discutir os parâmetros que afetam o aquecimento dos tecidos biológicos, decorrente da aplicação do US. MATERIAIS E MÉTODOS: Efetuou-se levantamento bibliográfico nas bases de pesquisa ISI WEB e SCOPUS. Foram selecionados os artigos, na língua inglesa, que tiveram como ponto central, o estudo da variação da temperatura após a aplicação do US em humanos. RESULTADOS: Foram observadas variações significativas em relação ao aumento de temperatura tecidual. Para a frequência de 3MHz, ocorre um aumento médio de 2,6 ºC nos tecidos superficiais; e para 1MHz, há um aumento médio de 1,7 ºC em tecidos profundos. Há um maior aquecimento do tecido em relação ao tamanho da ERA (área de radiação efetiva), quanto menor o tamanho maior o aquecimento. Também há um aumento da temperatura em relação às intensidades. Intensidades variando entre 0,5 a 3 W/cm² apresentam um acréscimo significativo de temperatura. Em relação à forma de aplicação, o gel proporciona melhor acoplamento, gerando maior aquecimento com um tempo de aplicação de cinco minutos - o tempo de aplicação deve ser adequado à área de tratamento e à densidade de potência. Entretanto, a velocidade de aplicação parece não modificar o aquecimento até 7-8 cm/s, mesmo que dispositivos diferentes aqueçam em níveis diferentes. CONCLUSÃO: Os parâmetros para a aplicação do US devem ser controlados e ajustados para produzir o aquecimento profundo dos tecidos considerando a variação entre dispositivos.

Variability in effective radiating area at 1 MHz affects ultrasound treatment intensity

BACKGROUND AND PURPOSE

Previous research has indicated that not all ultrasound transducers heat at equal rates; however, the cause of this disparity is unclear. Variability in spatial average intensity (SAI) has been implicated in this disparity at 3 MHz. This variability has not been explored at 1 MHz.

METHODS

Sixty-six 5-cm(2) ultrasound transducers were purchased from 6 different manufacturers. Transducers were calibrated and assessed for effective radiating area (ERA), total output power, and SAI using standardized measurement techniques.

RESULTS

Total output power values fell within US Food and Drug Administration guidelines, but there were large variations in ERA. The resulting SAI values showed large deviations (-43% to +61%) from the digitally displayed value. Intra-manufacturer SAI values varied up to 53%.

DISCUSSION AND CONCLUSION

Spatial average intensity can vary largely from the values displayed on these ultrasound generators; in a calibrated cohort, this difference is primarily attributable to differences in measured ERA. Patterns of SAI variability within the manufacturer at 1 MHz do not follow previous reports of variability at 3 MHz.

Effect of transducer velocity on intramuscular temperature during a 1-MHz ultrasound treatment

STUDY DESIGN

A 3 x 2 repeated-measures design was used. The independent variables were transducer velocity (2-3 cm/s, 4-5 cm/s, and 7-8 cm/s) and time (pretreatment and posttreatment).

OBJECTIVE

To determine if transducer velocity of a 1-MHz ultrasound treatment affects intramuscular tissue temperature.

BACKGROUND

Most authors advocate ultrasound transducer velocities of 2 to 4 cm/s within an area of 2 to 3 times the effective radiating area or 2 times the size of the transducer head. However, a much faster rate of application (approximately 7-8 cm/s) is often observed in clinical settings.

METHODS AND MEASURES

Eleven healthy screened volunteers (9 males, 2 females; mean +/- SD age, 22.6 +/- 1.7 years; mean +/- SD height, 175.7 +/- 13.7 cm; mean +/- SD body mass, 82.5 +/- 19.5 kg) were randomly assigned to a treatment order with all conditions administered during a single testing session. Each transducer velocity condition was administered for 10 minutes, using 1-MHz ultrasound with a 100% continuous duty cycle at an intensity of 1.5 W/cm2 over an area twice the size of the transducer head. After the first treatment, the 2 remaining subsequent velocity conditions were administered after the intramuscular temperature returned to within +/- 0.3 degrees C of the initial pretreatment temperature for 5 minutes. The dependent variable was left triceps surae muscle temperature measured at 3 cm below one half the measured skinfold thickness.

RESULTS

Temperature increase across the 3 velocities was within 0.4 degrees C (F2.20 = 0.07, P = .93). Posttreatment values (mean +/- SD) ranged from 42.7 degrees C +/- 2.3 degrees C for the slowest velocity to 43.1 degrees C +/- 1.4 degrees C for the fastest velocity. Temperature increase was significant for time (F1.01 = 155.68, P<.00001), increasing from 37.8 degrees C +/- 0.8 degrees C pretreatment to 42.9 degrees C +/- 1.9 degrees C after treatment.

CONCLUSION

Very similar intramuscular temperature increases can be observed among ultrasound treatments (10-minute duration, 1-MHz frequency, 100% continuous duty cycle, 1.5 W/cm2 intensity, within an area twice the size of the transducer head), with transducer velocities of 2 to 3, 4 to 5, and 7 to 8 cm/s.