27.4 A sub-1dB NF dual-channel on-coil CMOS receiver for Magnetic Resonance Imaging

Abstract

Magnetic Resonance Imaging (MRI) is a widely used medical imaging technique. It employs a strong static magnetic field (1.5 to 10.5T for human imaging) to split the spin states of the 1H nuclei in the body, and RF excitation to induce transitions and coherence among them. Gradient fields are superimposed to modulate the 1H resonance frequency, which enables spatially distinguishable signals to be picked up by RF receive coils. A high-field MRI provides better sensitivity and resolution but requires better receivers (RX), as signal DR and 1H resonance increase (128MHz for 3T, 300MHz for 7T). Overall sensitivity and imaging speed can be enhanced by closely surrounding the target anatomy with tens of RX coils (as in MIMO) [1], at the expense of as many shielded RF cables to carry the information out of the field. Progress in PCB size has allowed multi-channel RX to be placed inside the magnetic field (in-bore), reducing the RF cable length to less than 1m [2,3]. Ultimately, the RX should be placed directly on-coil to avoid bulky coaxial cables and improve patient comfort and safety by acquiring data in-bore and sending them digitally to the MRI scanner via an optical fiber link. The latter is cheap, flexible and insensitive to magnetic fields. The immediate vicinity of the coils and the patient is, however, a hostile as well as sensitive electromagnetic environment, which tolerates only the smallest of PCBs and virtually no magnetic material in its components. Integration of the full RX chain in a CMOS chip, which is small, non-magnetic and low power, holds the key to the next wave of compact MRI coil arrays for advanced medical imaging. This paper presents a fully integrated dual-receiver RFIC for coil arrays intended for (ultra-) high field (1.5 to 10.5T and 64 to 450MHz) scanners for clinical MRI, where requirements are considerably stricter than previously reported transceiver ICs [4,5] on palm-held NMR devices for spectroscopy or lab-on-chip applications.