School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia.
College of Optoelectronic Engineering, Chongqing University, Chongqing 400030, People's Republic of China.
Phys Med Biol. 2019 Apr 5;64(8):085003. doi: 10.1088/1361-6560/ab084a.
Insertable head gradient coils offer significant advantages such as high gradient strength and fast gradient switching speed owing to shorter distances to the target region of interest than whole-body cylindrical coils. To produce superior gradient performance, the local head coil is typically designed with an asymmetric configuration to accommodate both the shoulders and head of a patient, leading to tough dimensional constraints and practical limits to the coil implementation. In this paper, we propose a new cone-shaped model to improve the performance of the asymmetric head coils and to mitigate patient claustrophobia. The primary coils are designed with a larger diameter at the patient end for access and a smaller diameter at the service end to bring wires closer to the human head, while the secondary coils are arranged on a cylindrical former to improve coil efficiency. Two cases are studied in this paper. Case I: inner bore size at the patient end (diameter 42 cm) is fixed as the design reference. In this case, inner diameters at any other position vary with the conical tilting angles. Compared with a set of conical gradient coils designed with tilting angles ranging from 0 to 14°, it is found that the optimal coil performance is achieved at the tilting angle of 14°. The key performance parameters have been improved by 100%-200% for the transverse coils, and about 50% for the longitudinal coils compared with the cylindrical counterpart with the reference bore size (that is, the same diameter of 42 cm). The conical coils also produce less heat in the gradient structure and lower acoustic noise in the field of view. Case II: inner bore size at the iso-centre (diameter 34 cm) is set as the design reference. It is also found that, compared with 34 cm diameter cylindrical coils, the conical transverse coil performance has been improved at an angle of 14°. The key coil performance increases by 20%-50% for transverse coil but decreases by 20%-40% for the longitudinal coil. However, compared with the tight cylindrical structure (e.g. 34 cm diameter), the tilting angle will provide patient-friendly space for imaging and handling, which can be critical for fMRI and other brain studies.
插入式头部梯度线圈由于与感兴趣的目标区域的距离比全身圆柱线圈短，因此具有更高的梯度强度和更快的梯度切换速度。为了产生优异的梯度性能，局部头部线圈通常采用非对称结构设计，以适应患者的肩部和头部，这导致了严格的尺寸限制和线圈实现的实际限制。在本文中，我们提出了一种新的锥形模型，以提高非对称头部线圈的性能并减轻患者幽闭恐惧症。初级线圈在患者端设计有较大的直径以方便进入，在服务端设计有较小的直径以使电线更接近人头，而次级线圈则排列在圆柱形模具上以提高线圈效率。本文研究了两种情况。情况 I：以患者端的内孔尺寸（直径 42cm）为固定设计参考。在这种情况下，任何其他位置的内径都随锥形倾斜角度而变化。与一组倾斜角度范围从 0 到 14°的锥形梯度线圈相比，发现最佳的线圈性能是在倾斜角度为 14°时实现的。与具有参考内孔尺寸（即相同直径 42cm）的圆柱型相比，横向线圈的关键性能参数提高了 100%-200%，纵向线圈提高了约 50%。锥形线圈在梯度结构中产生的热量也更少，视野中的声噪声也更低。情况 II：以等中心的内孔尺寸（直径 34cm）为设计参考。还发现，与 34cm 直径的圆柱线圈相比，在 14°的角度下，锥形横向线圈的性能得到了改善。横向线圈的关键线圈性能提高了 20%-50%，而纵向线圈的性能则降低了 20%-40%。然而，与紧密的圆柱结构（例如 34cm 直径）相比，倾斜角度将为成像和处理提供患者友好的空间，这对于 fMRI 和其他脑研究至关重要。
