Cryogenic Preamplifiers for Magnetic Resonance Imaging

Abstract

Pursuing the ultimate limit of detection in magnetic resonance imaging (MRI) requires cryogenics to decrease the thermal noise of the electronic circuits. As cryogenic coils for MRI are slowly emerging cryogenic preamplifiers are required to fully exploit their potential. A cryogenic preamplifier operated at 77 K is designed and implemented for C imaging at 3 T (32.13 MHz), using off-the-shelves components. The design is based on a high electron mobility transistor (ATF54143) in a common source configuration. Required auxiliary circuitry for optimal cryogenic preamplifier performance is also presented consisting of a voltage regulator (noise free supply voltage and optimal power consumption), switch, and trigger (for active detuning during transmission to protect the preamplifier). A gain of 18 dB with a noise temperature of 13.7 K is achieved. Performing imaging experiments in a 3 T scanner showed an 8% increased signal-to-noise ratio from 365 to 399 when lowering the temperature of the preamplifier from 296 to 77 K while keeping the coil at room temperature. This paper thus enables the merger of cryogenic coils and preamplifiers in the hopes of reaching the ultimate limit of detection for MRI.

Improved Decoupling for Low Frequency MRI Arrays Using Non-Conventional Preamplifier Impedance

“…In order to validate the analysis in the previous section, a simple 2-channel array was built, using wire loop coils (coil diameter 50 mm, wire diameter 2.3 mm) separated 75 mm center to center. Experiments were repeated using a commercial preamplifier with resistive low input impedance (WMA32C, WanTCom, Chanhassen, MN, USA), with the coils matched to 50 Ω and 100 Ω, and a self-developed preamplifier [5] with an input impedance Z PRE = (0.5+j67 Ω) and the coils matched to 50 Ω. The parameters of the preamplifiers are shown in Table 1.…”

“…The preamplifiers used were built using similar capacitors and inductors, including in this case also nonmagnetic resistors (Passive Plus, Huntington, NY, USA). A pHeMT transistor (ATF 58143, Broadcom, San Jose, CA, USA) was used as active element for the preamplifier, and biased in a common source fashion as described in [5]. The fabricated coil array is shown in Figure 7.a.…”

“…The coils were not overlapped with the purpose of improving the parallel imaging performance of the array. The realization is based on self-developed preamplifiers with input impedance Z PRE = (0.5+j67 Ω) [5].…”

PIN diode driver for NMR and MRI

“…Vice versa, when Vin transitions below a lower threshold V l , V ol = 0. R1, R2, R3, and R4 are found by solving [21]…”

Angular Dependence of InP High Electron Mobility Transistors for Cryogenic Low Noise Amplifiers under a magnetic field

“…Such ultra-sensitive microwave receivers are used in detector experiments of dark matter [2] and mass spectrometry [3]. A potential application is MRI where cryogenic LNAs can provide increased sensitivity [4]. Previous reports on the cryogenic LNA ha only reported on 0 or 90 o orientation versus magnetic field [5].…”