Sub-Sm–1 electromagnetic induction imaging with an unshielded atomic magnetometer

Abstract

Progress in electromagnetic induction imaging with atomic magnetometers has brought its domain to the edge of the regime useful for biomedical imaging. However, a demonstration of imaging below the required 1 Sm À1 level is still missing. In this Letter, we use an 87 Rb radio frequency atomic magnetometer operating near room temperature in an unshielded environment to image calibrated solutions mimicking the electric conductivity of live tissues. By combining the recently introduced near-resonant imaging technique with a dual radio frequency coil excitation scheme, we image 5 ml of solutions down to 0.9 Sm À1 . We measure a signal-to-noise ratio of 2.7 at 2 MHz for 0.9 Sm À1 , increased up to 7.2 with offline averaging. Our work is an improvement of 50 times on previous imaging results and demonstrates the sensitivity and stability in unshielded environments required for imaging biological tissues, in particular for the human heart.

Electromagnetic Induction Imaging with Atomic Magnetometers: Progress and Perspectives

“…This stimulated a continuous development of the performances of EMI-AM systems [35,36]. This rapidly led to the demonstration [37] of imaging of a few mL of calibrated saline solution with conductivity below 1 S/m, as required for biomedical imaging. Figure 4 illustrates this development from the early demonstrations to the state-of-the-art sensititivity measurements of [37] by reporting the milestones in the quest for extreme sensitivity to small volumes of low-conductive materials.…”

“…Among the various technical developments, two certainly played an essential role in reaching extreme sensitivity: the use of near-resonant imaging [35], and the introduction of the dual-coil configuration for the rf-field [36][37][38]. Near-resonant imaging consists in choosing the frequency of the rf field slightly different from exact atomic resonance.…”

“…A solution to this issue, already put forward in the context of MIT with inductive coils [1] and also implemented in the context of nuclear quadrupole resonance spectroscopy with RF-AMs [39], is the use of a dual-coil configuration, so to have a large field on the target object and a significantly reduced field driving the atomic spins. [26], filled square from [29], open diamonds from [30], filled triangle up from [22], filled triangle down from [40], filled triangle left from [41], filled triangle right [35], open squares from [36], closed disks from [37].…”

“…Filled diamonds data are from Ref [26],. filled square from[29], open diamonds from[30], filled triangle up from[22], filled triangle down from[40], filled triangle left from[41], filled triangle right[35], open squares from[36], closed disks from[37].…”

Electromagnetic Induction Imaging: Signal Detection Based on Tuned-Dressed Optical Magnetometry

“…In 2001, Griffiths [1] proposed an imaging technique based on inferring one or more of the three passive electromagnetic properties (conductivity σ, permittivity and permeability µ) to produce images on the basis of the response to a position dependent oscillating magnetic field. Several denominations are used to identify this kind of methodologies, among which electromagnetic induction imaging (EII) [2], electro-magnetic tomograhy (EMT) [3], magnetic induction tomography (MIT) [4,5], and also mutual inductance tomography (same acronym) [6], the latter three stressing the potential of the technique to provide 3D mapping. A review on the subject was recently authored by Ma and Soleimani [7].…”