Toward multi-channel magnetic resonance imaging with radio-frequency atomic magnetometers*

Radio-frequency atomic magnetometers (RF AMs) can operate in a broad frequency range from kHz to MHz with a magnetic field tuning. Their sub-fT sensitivity is promising for many applications, especially in magnetic resonance imaging (MRI). At Los Alamos, we have designed a multi-channel RF AMs with the goal of applications in

multi-channel parallel MRI at ultra-low field. A long-standing problem in MRI applications is that AM loses its sensitivity in the presence of the MRI fields and gradients. A simple solution, compatible with anatomical imaging, is to use a flux transformer (FT) that carries out only the RF component of MRI signals into the AM. In a multi-channel FT-OPM system, it is important to sufficiently reduce crosstalk between FTs. According to our analysis, an array of partially overlapping pick-up coils in a non-resonance operation can minimize

the mutual flux between the FTs. In contrast, an array of pick-up coils would require a resonant operation to reach fT sensitivity without AMs, which would make the FT

decoupling a very challenging technical problem. We performed theoretical simulations [1] to address the FT decoupling question and estimated the sensitivity of the multichannel

FT-AM system. In this talk, we will report our progress on the multi-channel MRI and related questions, such as design of low-noise 100 aT RF shield [2] from

which MRI and other high-sensitivity AM applications will greatly benefit. Recently, using RF shield and specially designed pick-up coil we improved the detection sensitivity inside the MRI scanner to that below 0.5 fT/Hz^1/2, resulting in 1 mm resolution images of a phantom in about 5 minute scan time.