Pre-amplifiers for a 15-Tesla magnetic resonance imager

Abstract

High-field magnetic resonance imagers (MRI) give better signal-to-noise ratio (SNR) and image contrast. However clinical MRIs are currently limited to 3 Tesla (T) magnetic field strength. To create an uncommon 15 T scanner for research use, we evaluated several low-cost, intended for wireless communication, GaAs enhancement-mode pseudomorphic high electron mobility transistors (ePHEMT) in the critical preamplifier slot. This paper reports the experimental results that were obtained at both module and system levels.When evaluated in our prototype 15 T scanner front-end's preamplifier slot, the candidate devices' sub 1dB noise figures enabled image SNR ~ 110 in a water phantom (test object) with a standard pulse sequence. Crisp and artifact-free images could be obtained with these candidate devices. In conclusion, high performance pre-amplifiers for 15 T MRIs can be realized using low cost ePHEMTs originally marketed for wireless communications.

MRI Fundamentals: RF Aspects of Magnetic Resonance Imaging (MRI)

“…Down-conversion mixers were used to lower the MRI signal to then-current analog-to-digital converter (ADC) conversion frequencies so that signal processing could be performed in the digital domain ( Figure 15). The current trend in MRI receivers is the use of multiple parallel channels and direct to digital conversion after the front-end amplifiers, similar to current technology drives to all digital receivers [42], [43]. In an MRI system, digital signals are often sent from the scan room to the equipment room, helping to minimize the noise pickup compared with previously analog-based signal relay techniques.…”

Cryogenic Preamplifiers for Magnetic Resonance Imaging

“…Publications and commercial products for room temperature preamplifiers for MRI is plentiful. C. Lim et al [12] describes three designs for 619 MHz. S. Yadav [13] presents simulations of a cascaded topology for 64 MHz.…”