An improved asymmetric gradient coil design for high-resolution MRI head imaging

Abstract

For head magnetic resonance imaging, local gradient coils are often used to achieve high solution images. To accommodate the human head and shoulder, the head gradient coils are usually designed in an asymmetric configuration, allowing the region-of-uniformity (ROU) close to the coil's patient end. However, the asymmetric configuration leads to technical difficulties in maintaining a high gradient performance for the insertable head coil with very limited space. In this work, we present a practical design configuration of an asymmetric insertable gradient head coil offering an improved performance. In the proposed design, at the patient end, the primary and secondary coils are connected using an additional radial surface, thus allowing the coil conductors distributed on the flange to ensure an improvement in the coil performance. At the service end, the primary and shielding coils are not connected, to permit access to shim trays, cooling system piping, cabling, and so on. The new designs are compared with conventional coil configurations and the simulation results show that, with a similar field quality in the ROU, the proposed coil pattern has improved construction characteristics (open service end, well-distributed wire pattern) and offers a better coil performance (lower inductance, higher efficiency, etc) than conventional head coil configurations.

Gradient and shim technologies for ultra high field MRI

“…However, PNS thresholds are already severely limiting the useable gradient performance for whole-body coils due to the larger area of tissue exposed to the rapidly switching fields, and only modest gains are expected in the future. It is especially for this reason that high-performance human-head-sized insertable GCs have been proposed (Chronik and Rutt, 1998; Chronik et al, 2000; Tomasi et al, 2002; Wong, 2012; Handler et al, 2014; Tang et al, 2016). A number of these designs are suitable for UHF but may not have the thermal and electrical performance to tolerate the high duty cycles, currents and slew rates required for high-quality UHF imaging.…”

Predicting in vivo MRI Gradient-Field Induced Voltage Levels on Implanted Deep Brain Stimulation Systems Using Neural Networks

“…Gradient coils with higher peak amplitude (G max ) and peak slew rate are desired to improve image quality and speed for echo planar imaging, diffusionweighted imaging and several other advanced imaging protocols (Le Bihan et al, 1986;Young et al, 1987;Turner et al, 1990;Wong et al, 1991;Basser and Pierpaoli, 1996), and significant research efforts are being carried out to develop such coils. Local head/neck gradient coils have been evaluated and developed to improve gradient performance compared to whole-body gradient coils (Alsop and Connick, 1996;Crozier et al, 1999;Chronik et al, 2000;Tang et al, 2016). High-performance research systems for imaging human brain connectivity and microstructure have been developed with G max of 300 mT/m (McNab et al, 2013) or slew rate of 1200 T/m/s (Weiger et al, 2018).…”

Lightweight, compact, and high‐performance 3T MR system for imaging the brain and extremities

“…3,4 Previous reports of smaller-diameter, dedicated headgradient coils have shown that the PNS threshold is substantially above that of whole-body gradients, allowing the use of gradient slew rates in excess of 200 T/m/s. [5][6][7] However, other head gradient coils developed for imaging the brain have not seen routine use, due either to deficiencies in active shielding, poor spatial linearity over the required 22-cm to 24-cm imaging FOV for brain imaging, 5,[8][9][10][11][12][13][14][15] gradient heating, or the additional concomitant fields produced by an asymmetric design. 16,17 Regions of the brain such as the frontal lobe and the cerebellum could not be imaged without distortion as a result of poor spatial gradient linearity.…”