A cone-shaped gradient coil design for high-resolution MRI head imaging

Abstract

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.

Acoustic Control through Gradient Coil Design Using a Finite-Difference-Based Method for MRI

“…Shao et al used analytical methods for noise analysis in cylindrical ducts [17,18]. Based on this method, Forbes et al proposed an analytical gradient coil design method to control acoustic noise [19,20].…”

Simplified H1 Coil With a Single Layer of Surface Conductors

“…Instead, a transformation or projection guaranteeing mathematical and physical equivalence would be preferable. Previous research has optimized coils, which could in principle also serve for deriving equivalent coils [41][42][43]52]. However, the use of a global optimization framework, typically including search heuristics, does not necessary guarantee equivalence and further appears computationally excessive if instead a forward projection transformation were possible, which is comparatively resource-efficient.…”

A contribution to MRI safety testing related to gradient‐induced heating of medical devices

“…This allows overcoming another limitation of the ISO/TS 10974, which currently prescribes to perform the tests using tabulated values of the root mean square of the time derivative of the magnetic field generated by the gradient coils. However, these values in the future could be no longer representative, considering the development of new technologies 32 and the introduction of new sequences, 33 therefore provoking the need for a continuous update of the standards in order to keep trace of the new reference values.…”