Tillander Matti, Hokland Steffen, Koskela Julius, Dam Høgni, Andersen Niels Peter, Pedersen Michael, Tanderup Kari, Ylihautala Mika, Köhler Max
MR-Therapy, Philips Healthcare, Uusimaa 01510, Finland.
Department of Clinical Medicine, Aarhus University Hospital, Aarhus 8000, Denmark.
Med Phys. 2016 Mar;43(3):1539-49. doi: 10.1118/1.4942378.
Mild hyperthermia can be used as an adjuvant therapy to enhance radiation therapy or chemotherapy of cancer. However, administering mild hyperthermia is technically challenging due to the high accuracy required of the temperature control. MR guided high-intensity focused ultrasound (MR-HIFU) is a technology that can address this challenge. In this work, accurate and spatially uniform mild hyperthermia is demonstrated for deep-seated clinically relevant heating volumes using a HIFU system under MR guidance.
Mild hyperthermia heating was evaluated for temperature accuracy and spatial uniformity in 11 in vivo porcine leg experiments. Hyperthermia was induced with a commercial Philips Sonalleve MR-HIFU system embedded in a 1.5T Ingenia MR scanner. The operating software was modified to allow extended duration mild hyperthermia. Heating time varied from 10 min up to 60 min and the assigned target temperature was 42.5 °C. Electronic focal point steering, mechanical transducer movement, and dynamic transducer element switch-off were exploited to enlarge the heated volume and obtain uniform heating throughout the acoustic beam path. Multiple temperature mapping images were used to control and monitor the heating. The magnetic field drift and transducer susceptibility artifacts were compensated to enable accurate volumetric MR thermometry.
The obtained mean temperature for the target area (the cross sectional area of the heated volume at focal depth primarily used to control the heating) was on average 42.0 ± 0.6 °C. Temperature uniformity in the target area was evaluated using T10 and T90, which were 43.1 ± 0.6 and 40.9 ± 0.6 °C, respectively. For the near field, the corresponding temperatures were 39.3 ± 0.8 °C (average), 40.6 ± 1.0 °C (T10), and 38.0 ± 0.9 °C (T90). The sonications resulted in a concise heating volume, typically in the shape of a truncated cone. The average depth reached from the skin was 86.9 mm. The results show that the heating algorithm was able to induce deep heating while keeping the near-field temperature uniform and at a safe level.
The capability of MR-HIFU to induce accurate, spatially uniform, and robust mild hyperthermia in large deep-seated volumes was successfully demonstrated through a series of in vivo animal experiments.
轻度热疗可作为辅助治疗手段，增强癌症的放射治疗或化疗效果。然而，由于温度控制要求高精度，实施轻度热疗在技术上具有挑战性。磁共振引导高强度聚焦超声（MR-HIFU）技术能够应对这一挑战。在本研究中，使用HIFU系统在磁共振引导下，针对深部临床相关加热体积，展示了精确且空间均匀的轻度热疗效果。
在11项猪腿部体内实验中，对轻度热疗的温度准确性和空间均匀性进行了评估。采用嵌入1.5T Ingenia磁共振扫描仪的商用飞利浦Sonalleve MR-HIFU系统诱导热疗。对操作软件进行了修改，以实现延长时长的轻度热疗。加热时间从10分钟到60分钟不等，设定的目标温度为42.5°C。利用电子焦点转向、机械换能器移动和动态换能器元件关闭来扩大加热体积，并在整个声束路径上实现均匀加热。使用多个温度映射图像来控制和监测加热过程。对磁场漂移和换能器敏感性伪影进行了补偿，以实现精确的体积磁共振测温。
目标区域（主要用于控制加热的焦深处加热体积的横截面积）的平均温度为42.0±0.6°C。使用T10和T90评估目标区域的温度均匀性，分别为43.1±0.6°C和40.9±0.6°C。对于近场，相应温度分别为39.3±0.8°C（平均）、40.6±1.0°C（T10）和38.0±0.9°C（T90）。超声处理产生了简洁的加热体积，通常呈截头圆锥形状。从皮肤到加热区域的平均深度为86.9毫米。结果表明，加热算法能够实现深部加热，同时保持近场温度均匀且处于安全水平。
通过一系列体内动物实验，成功证明了MR-HIFU在大型深部体积中诱导精确、空间均匀且稳定的轻度热疗的能力。
