Saniour Isabelle, Authelet Gilles, Baudouy Bertrand, Dubuisson Rose-Marie, Jourdain Laurène, Willoquet Georges, Darrasse Luc, Ginefri Jean-Christophe, Poirier-Quinot Marie
Université Paris-Saclay, CEA, CNRS, Inserm, BioMaps, Orsay, France.
Irfu, CEA, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France.
Rev Sci Instrum. 2020 May 1;91(5):055106. doi: 10.1063/1.5143107.
Small-sized High Temperature Superconducting (HTS) radiofrequency coils are used in a number of micro-magnetic resonance imaging applications and demonstrate a high detection sensitivity that improves the signal-to-noise ratio. However, the use of HTS coils could be limited by the rarity of cryostats that are suitable for the MR environment. This study presents a magnetic resonance (MR)-compatible and easily operated cryogen-free cryostat based on the pulse tube cryocooler technology for the cooling and monitoring of HTS coils below the temperature of liquid nitrogen. This cryostat features a real-time temperature control function that allows the precise frequency adjustment of the HTS coil. The influence of the temperature on the electrical properties, resonance frequency (f), and quality factor (Q) of the HTS coil was investigated. Temperature control is obtained with an accuracy of over 0.55 K from 60 K to 86 K, and the sensitivity of the system, extracted from the frequency measurement from 60 K to 75 K, is of about 2 kHz/K, allowing a fine retuning (within few Hz, compared to 10 kHz bandwidth) in good agreement with experimental requirements. We demonstrated that the cryostat, which is mainly composed of non-magnetic materials, does not perturb the electromagnetic field in any way. MR images of a 10 × 10 × 15 mm liquid phantom were acquired using the HTS coil as a transceiver with a spatial resolution of 100 × 100 × 300 µm in less than 20 min under experimental conditions at 1.5 T.
小型高温超导（HTS）射频线圈被应用于多种微磁共振成像应用中，并展现出高检测灵敏度，可提高信噪比。然而，HTS线圈的使用可能会受到适用于磁共振环境的低温恒温器稀缺的限制。本研究提出了一种基于脉冲管制冷机技术的与磁共振（MR）兼容且易于操作的无液氦低温恒温器，用于冷却和监测低于液氮温度的HTS线圈。该低温恒温器具有实时温度控制功能，可实现HTS线圈的精确频率调整。研究了温度对HTS线圈电性能、共振频率（f）和品质因数（Q）的影响。在60 K至86 K范围内，温度控制精度超过0.55 K，从60 K至75 K的频率测量中提取的系统灵敏度约为2 kHz/K，能够进行精细的重新调谐（在几赫兹范围内，与10 kHz带宽相比），与实验要求高度吻合。我们证明，主要由非磁性材料组成的低温恒温器不会对电磁场产生任何干扰。在1.5 T的实验条件下，使用HTS线圈作为收发器，在不到20分钟的时间内采集了尺寸为10×10×15 mm的液体模型的MR图像，空间分辨率为100×100×300 µm。
