Ultra‐high‐field RF coil development for evaluating upper extremity imaging applications

The purpose of this study is to develop and evaluate a custom‐designed 7  T MRI coil and explore its use for upper extremity applications. An RF system composed of a transverse electromagnetic transmit coil and an eight‐channel receive‐only array was developed for 7  T upper extremity applications. The RF system was characterized and evaluated using scattering parameters and B₁⁺ mapping. Finite difference time domain simulations were performed to evaluate the B₁⁺ field distribution and specific absorption rate for the forearm region of the upper extremity. High‐resolution 7  T images were acquired and compared with those at 3 T. The simulation and experimental results show very good B₁⁺ field homogeneity across the forearm. High‐resolution images of musculotendinous, osseocartilaginous, and neurovascular structures in the upper extremity are presented with T₁ volumetric interpolated breath‐hold examination, T₂ double‐echo steady state, T₂* susceptibility weighted imaging (SWI), diffusion tensor imaging, and time‐of‐flight sequences. Comparison between 3  T and 7  T is shown. Intricate contextual anatomy can be delineated in synovial, fibrocartilaginous, interosseous, and intraosseous trabecular structures of the forearm, as well as palmar and digital vascular anatomy (including microvascular detail in SWI). Ultra‐high‐field 7  T imaging holds great potential in improving the sensitivity and specificity of upper extremity imaging, especially in wrist and hand pathology secondary to bone, ligament, nerve, vascular, and other soft or hard tissue etiology.