目的探讨低声压超声调控的微泡空化对大鼠Walker-256肿瘤产生的血管效应。方法健康雄性SD大鼠26只,双侧大腿内侧细胞接种法移植Walker-256肿瘤52个,利用随机数字表法进行分组后,分别给予不同强度的治疗声压,即假照组（n=6）、200 k Pa组（n=12）、400 k Pa组（n=10）、600 k Pa组（n=12）、800 k Pa组（n=12）。超声治疗占空比1%,治疗时间5 min。各不同声压治疗组中半数肿瘤在超声辐照同时经尾静脉注射0.1 m L脂质微泡。治疗前后分别进行超声造影,利用Adobe Photoshop软件对图像进行灰阶定量分析,得到肿瘤造影峰值平均灰阶值。治疗结束后获取肿瘤标本行病理检查。结果假照组和各实验组在治疗前后的超声造影分析结果显示,肿瘤造影峰值平均灰阶值差异无统计学意义（P〉0.05）,但病理检查发现600 k Pa组肿瘤组织血浆外渗和轻度水肿,800 k Pa组肿瘤组织明显出血、水肿。结论低声压超声联合微泡对大鼠Walker-256肿瘤的血流灌注影响不大,但600-800 k Pa声压可引起血管通透性的增加。
Sub-harmonic component generated from microbubbles is proven to be potentially used in noninvasive blood pressure measurement. Both theoretical and experimental studies are performed in the present work to investigate the dependence of the sub-harmonic generation on the overpressure with different excitation pressure amplitudes and pulse lengths. With 4-MHz ultrasound excitation at an applied acoustic pressure amplitude of 0.24 MPa, the measured sub-harmonic amplitude exhibits a decreasing change as overpressure increases; while non-monotonic change is observed for the applied acoustic pressures of 0.36 MPa and 0.48 MPa, and the peak position in the curve of the sub-harmonic response versus the overpres- sure shifts toward higher overpressure as the excitation pressure amplitude increases. Furthermore, the exciting pulse with long duration could lead to a better sensitivity of the sub-harmonic response to overpressure. The measured results are ex- plained by the numerical simulations based on the Marmottant model. The numerical simulations qualitatively accord with the measured results. This work might provide a preliminary proof for the optimization of the noninvasive blood pressure measurement through using sub-harmonic generation from microbubbles.
The nonlinearity has significant effect on the ultrasonic therapy using phased ar- rays. A numerical approach is developed to calculate the nonlinear sound field generated from a phased array based on the Gaussian superposition technique. The parameters of the phased array elements are first estimated from the focal parameters using the inverse matrix algorithm; Then the elements are expressed as a set of Gaussian functions; Finally, the nonlinear sound field can be calculated using the Gaussian superposition technique. In the numerical simulation, a 64~ 1 phased array is used as the transmitter. In the linear case, the difference between the results of the Gaussian superposition technique and the Fresnel integral is less than 0.5%, which verifies the feasibility of the approach. In the nonlinear case, the nonlinear fields of single-focus modes and double-focus modes are calculated. The results reveal that the nonlinear effects can improve the focusing performance, and the nonlinear effects are related with the source pressures and the excitation frequencies.
Lesions in porcine liver tissues created by continuous high intensity focused ultrasound(HIFU)exposures in vitro are theoretically and experimentally investigated,with the transmitter moving along a linear path at a fixed speed.Numerical simulations of the lesion formation are performed based on the Khokhlov-Zabolotskaya-Kuznetov equation and the bio-heat equation.In order to verify the theoretical predictions,experiments are performed in the one-dimensional scanning mode to measure the cross-sectional area of lesions created in the in vitro porcine liver exposed to 1.01-MHz HIFU pulses with the acoustic power of 70 W.The results indicate that,compared to the traditional discrete treatment protocol,the application of a continuous scanning model can create more uniform lesions in tissues and significantly reduces the total treatment time from 47 s to 30 s.
