A New CMOS Broadband, High Impedance LNA for MRI Achieving an Input Referred Voltage Noise Spectral Density of 200pV/Hz√

In this paper, we present a new architecture for the receive-chain in clinical X-nuclei magnetic resonance imaging (MRI) experiments. The proposed architecture requires only a single tuning capacitor to tune the MRI receive coil to the Larmor frequency of the nucleus of interest. The tuning capacitor provides a noise-free preamplification of the MR signal, allowing for relaxed noise constraints in the design of the following high impedance low noise amplifier (LNA). Together with the new architecture, we present a custom designed CMOS LNA with a passband between 1.5 MHz and 90 MHz, covering all clinically relevant nuclei in a 1.5 T MRI system. The custom designed LNA comprises two amplification stages providing a measured total gain of 44 dB and an on-chip DC servo loop to mitigate the effect of offsets in the presence of the large on-chip DC gain. The DC servo loop introduces a measured lower passband frequency at 1.5 MHz. The LNA displays a measured low input referred voltage noise spectral density of 200 pV/√Hz. X-nuclei MRI experiments performed on proton and fluor samples demonstrate the excellent performance of the proposed architecture and LNA implementation.