共查询到18条相似文献,搜索用时 78 毫秒
1.
由于颅骨形状不规则,声速、密度等声学参数分布不均匀,使用传统相控聚焦的方法进行经颅超声精确聚焦时会出现焦点偏移、焦点形状畸变、散焦的现象,时间反转法被认为是能够克服颅骨非均匀特性,实现经颅聚焦的有效手段。而利用传统有限元,有限差分法进行数值仿真时,往往需要划分十分精密的网格进行计算,耗费大量的时间。K空间伪谱法通过在空间域上进行傅里叶变换,时间域上进行有限差分的方法求解声波方程,能够在降低计算网格密度的同时保证计算精度。为了克服颅骨对聚焦超声造成的焦移影响,同时避免声学模型计算量过大的问题,本文使用Matlab K-wave开源工具箱,对食蟹猴颅骨CT数据进行三维声学建模,实现了基于时间反转法的经颅超声聚焦,讨论了时间反转法对于颅骨不规则形状及非均匀声速造成的焦移的补偿。仿真结果表明,K-wave在提高计算速度的同时能够服务于精准经颅超声聚焦,且相较于传统基于声时差法的相控聚焦方法,时间反转法在预设焦点位置,焦点强度更高,焦斑形状更为规则,聚焦效果更好。 相似文献
2.
文章以颅内血管分布为切入点,结合脉冲多普勒测量血流的原理,分析得出距离选通是超声经颅多普勒血流分析仪的重要计量性能参数,进而阐述采用弦线式测试件校准超声经颅多普勒血流分析仪距离选通参数的方法,并依据该方法对不同型号的超声经颅多普勒血流分析仪的距离选通参数进行校准,获得距离选通误差的测量结果,并以使用手册中公布的距离选通误差为标准要求,结合实际使用需求,对距离选通误差的测量结果进行计量确认,从而对本文的校准方法进行了实验验证。 相似文献
3.
4.
5.
6.
目前,超声清洗机通常是将一组换能器排布于平面式清洗槽底部,但用此方法会形成驻波现象,不利于超声清洗。文章提出了一种球面式聚焦超声清洗的方法,与普通超声清洗相比,该方法提高了超声清洗的效率。文章采用有限元COMSOL Multiphysics软件对清洗机内声场进行分析,得到三维模型内声压的分布情况;研制了聚焦超声清洗机,并通过薄膜腐蚀实验验证了清洗机内的声压分布情况;通过对比试验发现,聚焦超声清洗油污的速度比普通超声清洗提高了77.27%。通过薄膜腐蚀实验和超声清洗实验可知,聚焦超声清洗机内声场分布均匀,且声场内存在能量聚焦区域,清洗速率高于普通超声清洗机。 相似文献
7.
高强度聚焦超声(High Intensity Focused Ultrasound,HIFU)消融实体肿瘤已在临床治疗中展示出良好的应用前景。HIFU消融肿瘤技术由于其使靶区肿瘤组织瞬时升温至60℃以上,产生不可逆性凝固性坏死,同时不影响靶区外正常组织而被广泛应用。目前治疗用超声主要使用单频率高强度聚焦超声,但其临床应用的主要限制是靶区组织消融时间较长,靶区外正常组织损伤风险较大。缩短靶区组织消融时间,对于提高HIFU治疗效率,更好地应用于临床较为关键。在总结HIFU换能器的特性和影响HIFU治疗因素的基础上,综述了应用不同类型的双频HIFU换能器强空化和缩短靶区组织消融时间等方面的研究进展。 相似文献
8.
9.
10.
动态聚焦超声换能器的研究与设计 总被引:1,自引:0,他引:1
介绍了为超声激活血卟啉抗肿瘤效应而研究的动态聚焦超声换能器。它是由6个等间距,等宽度的同心圆环和1个中心圆片组成的7元平面 能器阵。通过改变辐射孔径和每个阵元电激励信号的延迟时间,实现动态聚焦衣在各聚焦处声强度一致,导出了聚焦声场声压分布表达式,并设计出换能器的具体结构参数。 相似文献
11.
12.
13.
Evaluation of polyvinyl alcohol cryogel as an acoustic coupling medium for low‐intensity transcranial focused ultrasound 下载免费PDF全文
Wonhye Lee Stephanie D. Lee Michael Y. Park Jaechun Yang Seung‐Schik Yoo 《International journal of imaging systems and technology》2014,24(4):332-338
Transcranial focused ultrasound (FUS) has emerged as a noninvasive neuromodulatory modality with exquisite depth penetration and spatial selectivity. Liquids, such as degassed water or mineral oil, are used as acoustic coupling media between the ultrasound‐generating transducer and the brain; however, they require a separate container that limits the spatial orientation of the transducers with respect to the sonication target. Nonliquid, gel‐like materials that do not require a housing container have been sought after as coupling media to overcome such limitations. Polyvinyl alcohol (PVA), when dissolved in water and undergone freeze–thaw cycle(s), forms a flexible hydrogel having a high level of acoustic transmission. To examine the feasibility of the PVA cryogel as the coupling material for transcranial FUS, the mechanical properties (in terms of its Young's modulus) and acoustic attenuation of the PVA cryogel were examined using different concentrations and number of freeze–thaw cycles. The cryogel with 6 or 7% (w/v) concentrations and two freeze–thaw cycles showed minimum pressure attenuation (on the order of 1%) across the different ultrasound frequencies (250–650 kHz). The cryogel was molded to fit around a single‐element FUS transducer and was applied to a head phantom, showing the flexibility in orienting the sonication paths at different angles and depths. The use of the cryogel did not alter the location and shape of acoustic focal profile compared to the one measured in the degassed water. The present work suggests that PVA cryogel may be used as an alternative acoustic coupling medium for low‐intensity FUS applications. 相似文献
14.
15.
Petros X. E. Mouratidis Marcia Costa Ian Rivens Elizabeth E. Repasky Gail ter Haar 《Journal of the Royal Society Interface》2021,18(180)
Pulsed high-intensity focused ultrasound (pHIFU) uses acoustic pressure to physically disrupt tumours. The aim of this study was to investigate whether pHIFU can be used in combination with immune checkpoint inhibitors (ICIs) to enhance survival of tumour-bearing animals. Murine orthotopic pancreatic KPC tumours were exposed both to a grid of pHIFU lesions (peak negative pressure = 17 MPa, frequency = 1.5 MHz, duty cycle = 1%, 1 pulse s−1, duration = 25 s) and to anti-CTLA-4/anti-PD-1 antibodies. Acoustic cavitation was detected using a weakly focused passive sensor. Tumour dimensions were measured with B-mode ultrasound before treatment and with callipers post-mortem. Immune cell subtypes were quantified with immunohistochemistry and flow cytometry. pHIFU treatment of pancreatic tumours resulted in detectable acoustic cavitation and increased infiltration of CD8+ T cells in the tumours of pHIFU and pHIFU + ICI-treated subjects compared with sham-exposed subjects. Survival of subjects treated with pHIFU + ICI was extended relative to both control untreated subjects and those treated with either pHIFU or ICI alone. Subjects treated with pHIFU + ICI had increased levels of CD8+IFNγ+ T cells, increased ratios of CD8+IFNγ+ to CD3+CD4+FoxP3+ and CD11b+Ly6G+ cells, and decreased CD11chigh cells in their tumours compared with controls. These results provide evidence that pHIFU combined with ICI may have potential for use in pancreatic cancer therapy. 相似文献
16.
17.
18.
治疗超声技术被推选为当今世界的前沿科学技术。高强聚焦超声(High Intensity Focused Ultrasound,HIFU)技术被认为是21世纪治疗肿瘤的新技术,已被成功地用于临床"消融"多种肿瘤。我国在使用聚焦超声技术治疗妇科外阴白色病、宫颈炎等也取得巨大成功,引起广泛重视。但这些新的治疗技术仍有很大的发展空间。并且指出了存在的问题和面临的挑战,以及为确保我国在这一领域的领先地位需要采取的应对措施。 相似文献