Seo Hyeon, Huh Hyungkyu, Lee Eun-Hee, Park Juyoung
Medical Device Development Center, Daegu-Gyeongbuk Medical Innovation Foundation, Daegu 41061, Korea.
Department of High-Tech Medical Device, College of Future Industry, Gachon University, Seongnam-si 13120, Korea.
Brain Sci. 2022 Feb 4;12(2):216. doi: 10.3390/brainsci12020216.
Focused ultrasound is a promising therapeutic technique, as it involves the focusing of an ultrasonic beam with sufficient acoustic energy into a target brain region with high precision. Low-intensity ultrasound transmission by a single-element transducer is mostly established for neuromodulation applications and blood-brain barrier disruption for drug delivery. However, transducer positioning errors can occur without fine control over the sonication, which can affect repeatability and lead to reliability problems. The objective of this study was to determine whether the target brain region would be stable under small displacement (0.5 mm) of the transducer based on numerical simulations. Computed-tomography-derived three-dimensional models of a rat head were constructed to investigate the effects of transducer displacement in the caudate putamen (CP) and thalamus (TH). Using three different frequencies (1.1, 0.69, and 0.25 MHz), the transducer was displaced by 0.5 mm in each of the following six directions: superior, interior, anterior, posterior, left, and right. The maximum value of the intracranial pressure field was calculated, and the targeting errors were determined by the full-width-at-half-maximum (FWHM) overlap between the free water space (FWHM) and transcranial transmission (FWHM). When the transducer was positioned directly above the target region, a clear distinction between the target regions was observed, resulting in 88.3%, 81.5%, and 84.5% FWHM for the CP and 65.6%, 76.3%, and 64.4% FWHM for the TH at 1.1, 0.69, and 0.25 MHz, respectively. Small transducer displacements induced both enhancement and reduction of the peak pressure and targeting errors, compared with when the transducer was displaced in water. Small transducer displacement to the left resulted in the lowest stability, with 34.8% and 55.0% targeting accuracy (FWHM) at 1.1 and 0.69 MHz in the TH, respectively. In addition, the maximum pressure was reduced by up to 11% by the transducer displacement. This work provides the targeting errors induced by transducer displacements through a preclinical study and recommends that attention be paid to determining the initial sonication foci in the transverse plane in the cases of small animals.
聚焦超声是一种很有前景的治疗技术，因为它能够将具有足够声能的超声束高精度地聚焦到目标脑区。单元素换能器的低强度超声传输大多用于神经调节应用以及破坏血脑屏障以实现药物递送。然而，如果对超声处理缺乏精细控制，就可能出现换能器定位误差，这会影响可重复性并导致可靠性问题。本研究的目的是基于数值模拟确定在换能器小位移（0.5毫米）情况下目标脑区是否稳定。构建了源自计算机断层扫描的大鼠头部三维模型，以研究换能器在尾状壳核（CP）和丘脑（TH）中的位移影响。使用三种不同频率（1.1、0.69和0.25兆赫），换能器在以下六个方向上各位移0.5毫米：上方、下方、前方、后方、左侧和右侧。计算颅内压力场的最大值，并通过自由水空间（半高宽）与经颅传输（半高宽）之间的半高宽重叠来确定靶向误差。当换能器直接位于目标区域上方时，观察到目标区域之间有明显区别，在1.1、0.69和0.25兆赫时，CP的半高宽分别为88.3%、81.5%和84.5%，TH的半高宽分别为65.6%、76.3%和64.4%。与换能器在水中位移时相比，换能器的小位移会导致峰值压力和靶向误差的增强和降低。换能器向左的小位移导致稳定性最低，在1.1和0.69兆赫时，TH中的靶向精度（半高宽）分别为34.8%和55.0%。此外，换能器位移使最大压力降低了多达11%。这项工作通过临床前研究提供了由换能器位移引起的靶向误差，并建议在小动物的情况下，在确定横向平面中的初始超声处理焦点时要予以关注。
