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Abstract：
OBJECTIVE: In this study, we examine the effects of a recently developed, iron-based coupling medium (IBCM) on guidance magnetic resonance (MR) scans during transcranial, magnetic-resonance-guided, focused ultrasound surgery (tMRgFUS) procedures. More specifically, this study tests the hypotheses that the use of the IBCM will (a) not adversely affect image quality, (b) remove aliasing from small field-of-view scans, and (c) decouple image quality from the motion state of the coupling fluid.
METHODS: An IBCM, whose chemical synthesis and characterization are reported elsewhere, was used as a coupling medium during tMRgFUS procedures on gel phantoms. Guidance magnetization-prepared rapid-gradient-echo (MP-RAGE), TSE, and GRE scans were acquired with fields of view of 28 and 18 cm. Experiments were repeated with the IBCM in several distinct flow states. GRE scans were used to estimate temperature time courses as a gel target was insonated. IBCM performance was measured by computing (i) the root mean square difference (RMSD) of TSE and GRE pixel values acquired using water and the IBCM, relative to the use of water; (ii) through-time temperature uncertainty for GRE scans; and (iii) Bland-Altman analysis of the temperature time courses. Finally, guidance TSE and GRE scans of a human volunteer were acquired during a separate sham tMRgFUS procedure. As a control, all experiments were repeated using a water coupling medium.
RESULTS: Use of the IBCM reduced RMSD in TSE scans by a factor of 4 or more for all fields of view and nonstationary motion states, but did not reduce RMSD estimates in MP-RAGE scans. With the coupling media in a stationary state, the IBCM altered estimates of temperature uncertainty relative to the use of water by less than 0.2°C. However, with a high flow state, the IBCM reduced temperature uncertainties by the statistically significant amounts (at the 0.01 level) of 0.5°C (28 cm field of view) and 5°C (18 cm field of view). Bland-Altman analyses found a 0.1°C ± 0.5°C difference between temperature estimates acquired using water and the IBCM as coupling media. Finally, scans of a human volunteer using the IBCM indicate more conspicuous grey/white matter contrast, a reduction in aliasing, and a less than 0.2°C change in temperature uncertainty.
CONCLUSIONS: The use of an IBCM during tMRgFUS procedures does not adversely affect image quality for TSE and GRE scans, can decouple image quality from the motion state of the coupling fluid, and can remove aliasing from scans where the field of view is set to be much smaller than the spatial extent of the coupling fluid.
METHODS: An IBCM, whose chemical synthesis and characterization are reported elsewhere, was used as a coupling medium during tMRgFUS procedures on gel phantoms. Guidance magnetization-prepared rapid-gradient-echo (MP-RAGE), TSE, and GRE scans were acquired with fields of view of 28 and 18 cm. Experiments were repeated with the IBCM in several distinct flow states. GRE scans were used to estimate temperature time courses as a gel target was insonated. IBCM performance was measured by computing (i) the root mean square difference (RMSD) of TSE and GRE pixel values acquired using water and the IBCM, relative to the use of water; (ii) through-time temperature uncertainty for GRE scans; and (iii) Bland-Altman analysis of the temperature time courses. Finally, guidance TSE and GRE scans of a human volunteer were acquired during a separate sham tMRgFUS procedure. As a control, all experiments were repeated using a water coupling medium.
RESULTS: Use of the IBCM reduced RMSD in TSE scans by a factor of 4 or more for all fields of view and nonstationary motion states, but did not reduce RMSD estimates in MP-RAGE scans. With the coupling media in a stationary state, the IBCM altered estimates of temperature uncertainty relative to the use of water by less than 0.2°C. However, with a high flow state, the IBCM reduced temperature uncertainties by the statistically significant amounts (at the 0.01 level) of 0.5°C (28 cm field of view) and 5°C (18 cm field of view). Bland-Altman analyses found a 0.1°C ± 0.5°C difference between temperature estimates acquired using water and the IBCM as coupling media. Finally, scans of a human volunteer using the IBCM indicate more conspicuous grey/white matter contrast, a reduction in aliasing, and a less than 0.2°C change in temperature uncertainty.
CONCLUSIONS: The use of an IBCM during tMRgFUS procedures does not adversely affect image quality for TSE and GRE scans, can decouple image quality from the motion state of the coupling fluid, and can remove aliasing from scans where the field of view is set to be much smaller than the spatial extent of the coupling fluid.
摘要：
目的：在本研究中，我们研究了最近开发的，铁基耦合介质（IBCM）在经颅引导磁共振（MR）扫描，磁共振引导，聚焦超声手术（tMRgFUS）程序。更具体地说,这项研究测试了以下假设：使用IBCM（a）不会对图像质量产生不利影响，(b)消除小视场扫描的混叠现象，以及(c)将图像质量与耦合流体的运动状态解耦。
方法：IBCM，其化学合成和表征在其他地方报道，在凝胶体模上的tMRgFUS程序中用作偶联介质。引导磁化制备的快速梯度回波（MP-RAGE），TSE,和GRE扫描获得28和18厘米的视野。用IBCM在几种不同的流动状态下重复实验。GRE扫描用于估计温度时间进程，因为凝胶目标被超声处理。通过计算（i）使用水和IBCM获取的TSE和GRE像素值的均方根差（RMSD）来测量IBCM性能，（ii）GRE扫描的时间温度不确定性；（iii）温度时间过程的Bland-Altman分析。最后,在单独的假tMRgFUS手术期间,获得了一名志愿者的指导TSE和GRE扫描.作为一种控制，使用水耦合介质重复所有实验。
结果：对于所有视场和非平稳运动状态，使用IBCM将TSE扫描中的RMSD减少了4倍或更多，但并未降低MP-RAGE扫描中的RMSD估计值。在耦合介质处于静止状态的情况下，IBCM将与水使用相关的温度不确定性估计改变了小于0.2°C。然而,在高流量状态下，IBCM将温度不确定性降低了0.5°C（28cm视野）和5°C（18cm视野）的统计学显着量（0.01水平）。Bland-Altman分析发现，使用水和IBCM作为耦合介质获得的温度估计值之间存在0.1°C±0.5°C的差异。最后,使用IBCM的人类志愿者扫描显示更明显的灰/白质对比，减少别名，温度不确定度变化小于0.2°C。
结论：在tMRgFUS过程中使用IBCM不会对TSE和GRE扫描的图像质量产生不利影响，可以将图像质量与耦合流体的运动状态分离，并且可以从扫描中去除混叠，其中视场设置为远小于耦合流体的空间范围。
方法：IBCM，其化学合成和表征在其他地方报道，在凝胶体模上的tMRgFUS程序中用作偶联介质。引导磁化制备的快速梯度回波（MP-RAGE），TSE,和GRE扫描获得28和18厘米的视野。用IBCM在几种不同的流动状态下重复实验。GRE扫描用于估计温度时间进程，因为凝胶目标被超声处理。通过计算（i）使用水和IBCM获取的TSE和GRE像素值的均方根差（RMSD）来测量IBCM性能，（ii）GRE扫描的时间温度不确定性；（iii）温度时间过程的Bland-Altman分析。最后,在单独的假tMRgFUS手术期间,获得了一名志愿者的指导TSE和GRE扫描.作为一种控制，使用水耦合介质重复所有实验。
结果：对于所有视场和非平稳运动状态，使用IBCM将TSE扫描中的RMSD减少了4倍或更多，但并未降低MP-RAGE扫描中的RMSD估计值。在耦合介质处于静止状态的情况下，IBCM将与水使用相关的温度不确定性估计改变了小于0.2°C。然而,在高流量状态下，IBCM将温度不确定性降低了0.5°C（28cm视野）和5°C（18cm视野）的统计学显着量（0.01水平）。Bland-Altman分析发现，使用水和IBCM作为耦合介质获得的温度估计值之间存在0.1°C±0.5°C的差异。最后,使用IBCM的人类志愿者扫描显示更明显的灰/白质对比，减少别名，温度不确定度变化小于0.2°C。
结论：在tMRgFUS过程中使用IBCM不会对TSE和GRE扫描的图像质量产生不利影响，可以将图像质量与耦合流体的运动状态分离，并且可以从扫描中去除混叠，其中视场设置为远小于耦合流体的空间范围。
