Broadbands Four-Branch Hybrid Coupler-Based T/R Switch for 7-Tesla Magnetic Resonance Imaging

Abstract

In this article, we are introducing a new broadband four-branch microstripline hybrid coupler-based switch to transmit/receive signals of a wide range of operating frequencies to/from a single or multi-tuned radio frequency coil. The proposed switch has two ranges of frequencies covering many X-atomic nuclei including: 23Na, 31P, 19F, 13C, 7Li, and 1H when they are exposed to 7 Tesla magnetic field strength in magnetic resonance imaging machines. The introduced switch does not need any type of tuning to cover the X-nuclei. The introduced switch does not exceed the realistic trace width of microstriplines that determine the allowable amount of increase in temperature when being exposed to 1 kW power and 10% duty cycles of the radio frequency pulses. Electromagnetic wave simulator (ADS) is used to characterize the S-parameters. The fundamental and third harmonic center frequencies are adjusted to resonate with two broadbands covering the speed of precession of a wide range of X-nuclei. These atomic nuclei are used as a measure to the existence of cancerous tissues, and their targeting might reduce the need for biopsy in diagnosis. The introduced switch can conduct broadband signals to/from a multi-tuned coil with low return loss values (-15 to -27 dB), low insertion loss (from -0.64 to -1.29 dB), and very good isolation, amounts to -70 dB.