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 S m −1 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 S m −1 . We measure a signal-to-noise ratio of 2.7 at 2 MHz for 0.9 S m −1 , 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.Recent years have seen a vast increase in the applications of quantum technologies and, in particular, atomic magnetometers 1 to the biomedical field.Notable examples include magnetocardiography 2-5 and magnetoencephalography 4,6,7 . Applications for monitoring the reactivity of the nervous system have been also reported 8 . In all cases, the superior performance of the atomic magnetometers pushes existing technologies and diagnostic methods towards their fundamental limits.However, mapping the electric conductivity of biological tissues -and in particular of the human heart -is still an open issue. To date, no diagnostic tool is capable of non-invasively mapping the conductivity of cardiac tissue 9 . Current investigations require the invasive recording of activation potentials via surgically introduced electrodes. This does not allow direct mapping of conductivity, and presents issues due to the inconsistent adhesion of electrodes to the inner surface of the beating heart 10 .Electromagnetic induction imaging -often referred to as magnetic induction tomography 11 to highlight its tomographic capabilities -has been proposed as a diagnostic tool for various conditions characterized by a variation or an anomaly in electric conduction [12][13][14][15] . With this technique, eddy currents are excited in the specimen under investigation by an AC magnetic field (primary field). The response, containing information about the electric conductivity, electric permittivity, and magnetic permeability of the specimen, is detected via the magnetic field generated by the eddy currents (secondary field). One of the main limitations of this approach is the limited sensitivity of the magnetic field sensors in use. Therefore, until recently, detection and imaging were limited to relatively large samples 16 , in most cases well above usea) Electronic mail: l.marmugi@ucl.ac.uk ful volumes for medical applications. This issue was potentially solved by the demonstration of electromagnetic induction imaging with atomic magnetometers [17][18][19] . The higher sensitivity of the core sensor paved the path ...

Atrial Fibrillation (AF) affects a significant fraction of the ageing population, causing a high level of morbidity and mortality. Despite its significance, the causes of AF are still not uniquely identified. This, combined with the lack of precise diagnostic and guiding tools, makes the clinical treatment of AF sub-optimal. We identify magnetic induction tomography as the most promising technique for the investigation of the causes of fibrillation and for its clinical practice. We therefore propose a novel optical instrument based on optical atomic magnetometers, fulfilling the requirements for diagnostic mapping of the heart’s conductivity. The feasibility of the device is here discussed in view of the final application. Thanks to the potential of atomic magnetometers for miniaturisation and extreme sensitivity at room temperature, a new generation of compact and non-invasive diagnostic instrumentation, with both bedside and intra-operative operation capability, is envisioned. Possible scenarios both in clinical practice and biomedical research are then discussed. The flexibility of the system makes it promising also for application in other fields, such as neurology and oncology.

We demonstrate magnetic induction tomography (MIT) with an all-optical atomic magnetometer. Our instrument creates a conductivity map of conductive objects. Both shape and size of the imaged samples compare very well with the actual shape and size. Given the potential of all-optical atomic magnetometers for miniaturization and extreme sensitivity, the proof-of-principle presented in this Letter opens up promising avenues in the development of instrumentation for MIT.Imaging is an essential capability in a wide range of applications, from medicine to industry and security. More than one century of development provided a variety of imaging techniques, such as X-ray imaging, nuclear magnetic resonance (NMR) imaging, and ultrasound-based diagnostic imaging, just to name a few. Different imaging techniques rely on different properties of the object of interest, and thus provide information about different characteristics. Whenever the electrical and magnetic properties are the characteristics of interest, magnetic induction tomography (MIT) [1] is the obvious choice, as it directly provides a map of the electrical and magnetic properties of an object. Therefore, such technique is complementary to conventional magnetic imaging, and extends its range. In fact, MIT finds direct application in the detection and imaging of metallic components, e.g. for the detection of cracks or characterization of the level of corrosion. It is also a promising technique for biomedical applications, as different tissues typically present different electrical characteristics [2].The ultimate performance of a MIT system depends on the magnetic field sensor used. While most of the MIT setups rely on a standard coil of wire, or an array of coils [3], a variety of advances in different directions have been reported. Miniaturization can be achieved with printed circuit board (PCB) coil technology [4], thin film technology [5], or with the use of giant magnetoresistance (GMR) sensors [6].In this Letter, we demonstrate MIT with all-optical atomic magnetometers. By inducing eddy currents in the object of interest, and then using an atomic magnetometer to perform position-resolved measurements (of the phase and magnitude of the magnetic field produced by these currents), we are able to produce a conductivity map of the object. Given that atomic magnetometers hold record sensitivity [7] and have the potential for extreme miniaturization [8][9][10], this Letter paves the way for ultra-sensitive high-resolution imaging systems, using arrays of atomic magnetometers operating in a MIT modality.The experimental apparatus is shown schematically in Fig. 1. The object of interest is placed on a horizontal flat nonconductive support, and can be moved manually. * Corresponding author: f.renzoni@ucl.ac.ukThe atomic magnetometer for magnetic field sensing is under the support. The sensor is a 5 cm long vapor cell filled with the naturally occurring mixture of 85 Rb and 87 Rb. The cell is coated with polydimethylsiloxane (PDMS), and filled with 5 Torr of argon g...

We demonstrate imaging of ferromagnetic carbon steel samples and we detect the thinning of their profile with a sensitivity of 0.1 mm using a Cs radio-frequency atomic magnetometer. Images are obtained at room temperature, in magnetically unscreened environments. By using a dedicated arrangement of the setup and active compensation of background fields, the magnetic disturbance created by the samples' magnetization is compensated. Proof-of-concept demonstrations of non-destructive structural evaluation in the presence of concealing conductive barriers are also provided. Relevant impact for steelwork inspection and health and usage monitoring without disruption of operation is envisaged, with direct benefit for industry, from welding in construction, to pipelines inspection and corrosion under insulation in the energy sector.

We demonstrate the penetration of thick metallic and ferromagnetic barriers for imaging of conductive targets underneath. Our system is based on an Rb radio-frequency atomic magnetometer operating in electromagnetic induction imaging modality in an unshielded environment. Detrimental effects, including unpredictable magnetic signatures from ferromagnetic screens and variations in the magnetic background, are automatically compensated by active compensation coils controlled by servo loops. We exploit the tunability and low-frequency sensitivity of the atomic magnetometer to directly image multiple conductive targets concealed by a 2.5 mm ferromagnetic steel shield and/or a 2.0 mm aluminium shield, in a single scan. The performance of the atomic magnetometer allows imaging without any prior knowledge of the barriers or the targets, and without the need of background subtraction. A dedicated edge detection algorithm allows automatic estimation of the targets' size within 3.3 mm and of their position within 2.4 mm. Our results prove the feasibility of a compact, sensitive and automated sensing platform for imaging of concealed objects in a range of applications, from security screening to search and rescue.