Sun L, Collins C M, Schiano J L, Smith M B, Smith N B
Department of Bioengineering, College of Engineering, The Pennsylvania State University, University Park, PA 16802.
Concepts Magn Reson Part B Magn Reson Eng. 2005 Oct;27B(1):51-63. doi: 10.1002/cmr.b.20046. Epub 2005 Oct 28.
Previous researchers have successfully demonstrated the application of temperature feedback control for thermal treatment of disease using MR thermometry. Using the temperature-dependent proton resonance frequency (PRF) shift, ultrasound heating for hyperthermia to a target organ (such as the prostate) can be tightly controlled. However, using fixed gain controllers, the response of the target to ultrasound heating varies with type, size, location, shape, stage of growth, and proximity to other vulnerable organs. To adjust for clinical variables, feedback self-tuning regulator (STR) and model reference adaptive control (MRAC) methods have been designed and implemented using real-time, online MR thermometry by adjusting the output power to an ultrasound array to quickly reach the hyperthermia target temperatures. The use of fast adaptive controllers in this application is advantageous because adaptive controllers do not require a priori knowledge of the initial tissue properties and blood perfusion and can quickly reach the steady-state target temperature in the presence of dynamic tissue properties (e.g., thermal conductivity, blood perfusion). This research was conducted to rapidly achieve and manage therapeutic temperatures from an ultrasound array using novel MRI-guided adaptive closed-loop controllers both in ex vivo and in vivo experiments. The ex vivo phantom experiments with bovine muscle (n = 5) show that within 6 ± 0.2 minutes, the tissue temperature increased by 8 ± 1.37°C. Using rabbits' (n = 5) thigh muscle, the in vivo experiments demonstrated the target temperature reached 44.5°C ± 1.2°C in 8.0 ± 0.5 minutes. The preliminary in vivo experiment with canine prostate hyperthermia achieved 43 ± 2°C in 6.5 ± 0.5 minutes. These results demonstrate that the adaptive controllers with MR thermometry are able to effectively track the target temperature with dynamic tissue properties.
先前的研究人员已成功证明了利用磁共振温度测量法将温度反馈控制应用于疾病的热疗。利用与温度相关的质子共振频率（PRF）偏移，可以严格控制用于将热疗施加到目标器官（如前列腺）的超声加热。然而，使用固定增益控制器时，目标对超声加热的反应会因类型、大小、位置、形状、生长阶段以及与其他易损器官的接近程度而有所不同。为了适应临床变量，已设计并实施了反馈自整定调节器（STR）和模型参考自适应控制（MRAC）方法，通过实时、在线磁共振温度测量法调整超声阵列的输出功率，以快速达到热疗目标温度。在此应用中使用快速自适应控制器具有优势，因为自适应控制器不需要预先了解初始组织特性和血液灌注情况，并且在存在动态组织特性（如热导率、血液灌注）的情况下能够快速达到稳态目标温度。本研究旨在通过在体外和体内实验中使用新型磁共振成像引导的自适应闭环控制器，快速实现并管理来自超声阵列的治疗温度。对牛肌肉进行的体外模型实验（n = 5）表明，在6±0.2分钟内，组织温度升高了8±1.37°C。使用兔子的大腿肌肉（n = 5）进行的体内实验表明，目标温度在8.0±0.5分钟内达到44.5°C±1.2°C。对犬前列腺热疗进行的初步体内实验在6.5±0.5分钟内达到了43±2°C。这些结果表明，带有磁共振温度测量法的自适应控制器能够在存在动态组织特性的情况下有效跟踪目标温度。
