Abstract
We evaluated a 16-channel loop + dipole (LD) transceiver antenna array with improved specific absorption rate (SAR) efficiency for 10.5 Tesla (T) human head imaging apsplications. Three different array designs with equal inner dimensions were considered: an 8-channel dipole antenna, an 8-channel loop, and a 16-channel LD antenna arrays. Signal-to-noise ratio (SNR) and B1 + efficiency (in units of μT per √W) were simulated and measured in 10.5 T magnetic resonance imaging (MRI) experiments. For the safety validation, 10 g SAR and SAR efficiency (defined as the B1 + over √ (peak 10 g SAR)) were calculated through simulation. Finally, high resolution porcine brain images were acquired with the 16-channel LD antenna array, including a fast turbo-spin echo (TSE) sequence incorporating B1 shimming techniques. Both the simulation and experiments demonstrated that the combined 16-channel LD antenna array showed similar B1 + efficiency compared to the 8-channel dipole antenna and the 8-channel loop arrays in a circular polarized (CP) mode. In a central 2 mm × 2 mm region of the phantom, however, the 16-channel LD antenna array showed an improvement in peak 10 g SAR of 27.5 % and 32.5 % over the 8-channel dipole antenna and the 8-channel loop arrays, respectively. We conclude that the proposed 16-channel head LD antenna array design is capable of achieving ~7% higher SAR efficiency at 10.5 T compared to either the 8-channel loop-only or the 8-channel dipole-only antenna arrays of the same dimensions.
Highlights
Noninvasive exploration of the human body using magnetic resonance imaging (MRI) benefits from ultra-high field (UHF) systems, which are capable of achieving higher signal-to-noise ratios (SNR) than the systems widely used within the current clinical market [1]–[6]
We propose the concept of a loop + dipole (LD) antenna array that combines the structure of loops and dipoles in each element
Table 1 indicates a similar range of S11 values for all three arrays, −12.5 dB to −36.5 dB for the 8-channel dipole antenna array, −15.1 dB to −22.1 dB for the 8-channel loop array, and −12 dB to −24.1 dB for the 16-channel LD antenna array
Summary
Noninvasive exploration of the human body using magnetic resonance imaging (MRI) benefits from ultra-high field (UHF) systems, which are capable of achieving higher signal-to-noise ratios (SNR) than the systems widely used within the current clinical market [1]–[6]. Numerous new applications for human brain imaging have been developed for UHF [7]–[9]. The short wavelength in the human body at such frequencies contributes to a significantly nonuniform field distribution [10]–[12]. Upon expanding the highest MR field strength from 4 tesla (T) [13] to 7 T [5], [12]. The associate editor coordinating the review of this manuscript and approving it for publication was G.
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