Ozhinsky Eugene, Kohi Maureen P, Ghanouni Pejman, Rieke Viola
Department of Radiology and Biomedical Imaging, University of California San Francisco, 185 Berry Street, Suite 350, Box 0946, San Francisco, CA 94143 USA.
Department of Radiology, Stanford University, Stanford, CA USA.
J Ther Ultrasound. 2015 Sep 11;3:15. doi: 10.1186/s40349-015-0036-5. eCollection 2015.
Near-field heating is a potential problem in focused ultrasound treatments, as it can result in thermal injury to skin, subcutaneous fat, and other tissues. Our goals were to determine if T2-based temperature mapping could be used reliably to measure near-field heating in adipose tissue and whether it is practical to perform such mapping during focused ultrasound treatments.
We investigated the dependence of T2 on temperature in ex vivo adipose tissue at 3T using a double-echo fast spin echo (FSE) sequence. We implemented and evaluated the T2-based temperature mapping technique in the adipose tissue of two healthy volunteers. Finally, we applied the technique during magnetic resonance-guided focused ultrasound (MRgFUS) treatments to measure near-field heating in eight patients with uterine fibroids.
Calibration experiments in porcine adipose tissue determined a temperature coefficient of 6.16 ms/°C during heating and 5.37 ms/°C during cooling. The volunteer experiments demonstrated a strong correlation between the skin temperature and T2-based temperature measurements in the fat layer. During the treatments of patients with uterine fibroids, we observed a measurable change in the T2 of fat tissue within the path of the ultrasound beam and a temperature increase of up to 15 °C with sustained heating of more than 10 °C.
Our results demonstrate the feasibility and importance of monitoring near-field heating in fatty tissues. The implementation of near-field monitoring between sonications can shorten treatments by reducing the cooling time. It can help improve safety by avoiding excessive heating in the near field.
近场加热是聚焦超声治疗中的一个潜在问题，因为它可能导致皮肤、皮下脂肪和其他组织的热损伤。我们的目标是确定基于T2的温度映射是否可可靠用于测量脂肪组织中的近场加热，以及在聚焦超声治疗期间进行这种映射是否可行。
我们使用双回波快速自旋回波（FSE）序列，在3T条件下研究了离体脂肪组织中T2对温度的依赖性。我们在两名健康志愿者的脂肪组织中实施并评估了基于T2的温度映射技术。最后，我们在磁共振引导聚焦超声（MRgFUS）治疗期间应用该技术，测量了8例子宫肌瘤患者的近场加热情况。
猪脂肪组织的校准实验确定加热期间温度系数为6.16 ms/°C，冷却期间为5.37 ms/°C。志愿者实验表明皮肤温度与脂肪层中基于T2的温度测量之间存在强相关性。在子宫肌瘤患者的治疗过程中，我们观察到超声束路径内脂肪组织的T2有可测量的变化，持续加热超过10°C时温度升高高达15°C。
我们的结果证明了监测脂肪组织近场加热的可行性和重要性。在超声照射间隙实施近场监测可通过减少冷却时间来缩短治疗时间。它有助于通过避免近场过度加热来提高安全性。
