Magnetocardiography Measurements with 4He Vector Optically Pumped Magnetometers at Room Temperature S
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Magnetocardiography measurements with 4He vector optically pumped magnetometers at room temperature S. Morales, M.C. Corsi, W. Fourcault, F. Bertrand, G. Cauffet, C. Gobbo, F. Alcouffe, F. Lenouvel, M. Le Prado, F. Berger, etal. To cite this version: S. Morales, M.C. Corsi, W. Fourcault, F. Bertrand, G. Cauffet, et al.. Magnetocardiography measure- ments with 4He vector optically pumped magnetometers at room temperature . Physics in Medicine and Biology, IOP Publishing, 2017, 10.1088/1361-6560/aa6459. cea-01560997 HAL Id: cea-01560997 https://hal-cea.archives-ouvertes.fr/cea-01560997 Submitted on 12 Jul 2017 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Home Search Collections Journals About Contact us My IOPscience Magnetocardiography measurements with 4He vector optically pumped magnetometers at room temperature This content has been downloaded from IOPscience. Please scroll down to see the full text. Download details: IP Address: 132.168.159.47 This content was downloaded on 15/03/2017 at 15:43 Manuscript version: Accepted Manuscript Morales et al To cite this article before publication: Morales et al, 2017, Phys. Med. 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When available, you can view the Version of Record for this article at: http://iopscience.iop.org/article/10.1088/1361-6560/aa6459 Page 1 of 12 AUTHOR SUBMITTED MANUSCRIPT - PMB-104536.R1 1 2 3 4 4 5 Magnetocardiography measurements with He vector 6 7 optically pumped magnetometers at room temperature 8 9 10 1* 1* 1 1 2 1 S. Morales , M.C. Corsi , W. Fourcault , F. Bertrand , G. Cauffet , C. Gobbo , 11 F. Alcouffe1, F. Lenouvel1, M. Le Prado1, F. Berger1, G. Vanzetto3,4 and E. Labyt1 12 1. CEA, LETI, MINATEC Campus, F-38054 Grenoble, France 13 2. Univ. Grenoble Alpes, G2Elab, F-38000 Grenoble, France; CNRS, 14 G2Elab, F-38000 Grenoble, France 15 3. Department of Cardiology, University Hospital, Grenoble, France 16 4. INSERM U1039, Bioclinic Radiopharmaceutics Laboratory, Grenoble, France 17 * These authors contributed equally to this work 18 19 E-mail: corresponding author [email protected] 20 21 In this paper, we present a proof of concept study which demonstrates for the first time the 4 22 possibility to record magnetocardiography (MCG) signals with He vector optically-pumped 23 magnetometers (OPM) operated in a gradiometer mode. Resulting from a compromise between 24 sensitivity, size and operability in a clinical environment, the developed magnetometers are 25 based on the parametric resonance of helium in zero magnetic field. Sensors are operated at 26 room-temperature and provide a tri-axis vector measurement of the magnetic field. Measured 27 sensitivity is around 210 fT/√Hz in the bandwidth [2 Hz; 300 Hz]. MCG signals from a 28 phantom and two healthy subjects are successfully recorded. Human MCG data obtained with 29 the OPMs are compared to reference electrocardiogram (ECG) recordings: similar heart rates, 30 shapes of the main patterns of the cardiac cycle (P/T waves, QRS complex) and QRS widths 31 are obtained with both techniques. 32 33 34 Keywords: Optically Pumped Magnetometers (OPM), helium, Magnetocardiography (MCG) 35 36 37 38 1. Introduction 39 Magnetocardiography is a contactless, non-invasive imaging technique which consists in measuring 40 the magnetic fields generated by the heart, about one million times smaller than the Earth's magnetic 41 field. Electrocardiography (ECG) and magnetocardiography (MCG) both demonstrate a high temporal 42 resolution. However, discontinuities of the electrical conductivity in body tissues (bones, fat layer) act 43 as a low pass spatial filter of electrical cardiac signals recorded in ECG. As a result, a current flowing 44 from a localized cardiac region produces an ECG effect at almost all surface electrodes. Consequently, 45 it is difficult to interpret spatial information like QT dispersion in ECG while multi-channels MCG 46 should allow a more sensitive assessment of the cellular dispersion of ventricular repolarization 47 (Antzelevitch et al., 1998). Multi-channels MCG are also useful to detect precordial magnetic fields 48 originating from many sites over the heart with a high signal to noise ratio and a good spatio-temporal 49 resolution (Ikefuji et al., 2007). Another advantage of MCG is its ability to detect the magnetic field 50 51 produced by intracellular and extracellular currents in cardiac tissue, while ECG only detects the 52 effects of currents flowing through the body tissue (Wikswo and Barach, 1982)(Koch and Haberkorn, 53 2001). Recent clinical trials have reported that MCG mapping is useful for identifying spatial current 54 dispersion patterns, as well as for characterizing and discriminating Brugada syndrome and complete 55 right bundle branch block (Kandori et al., 2004). MCG mapping has also been reported to provide a 56 higher statistical sensitivity than ECG, giving the opportunity to better diagnose cardiac arrhythmia 57 and coronary artery diseases (Fenici et al., 2013)(Kwong et al., 2013)(Park et al., 2005). MCG can 58 also play a critical role in the diagnosis of long QT syndrome in fetuses (Cuneo et al., 2013). MCG 59 systems are currently based on the use of ultra-sensitive Superconducting Quantum Interference 60 Devices (SQUIDs), with only one magnetic sensitive direction characterized by a magnetic sensitivity Accepted Manuscript AUTHOR SUBMITTED MANUSCRIPT - PMB-104536.R1 Page 2 of 12 1 2 3 4 of about 1-10 fT/√Hz (Sternickel and Braginski, 2006). Nevertheless, dissemination of this imaging 5 technique is hindered by the high cost of SQUID equipment both in terms of initial investment (more 6 than one M€), as well as operational constraints and maintenance cost (more than 100 k€/year). 7 Moreover due to the cryogenic cooling system based on helium, a thermal insulation layer of a few 8 centimeters is required between the skin and the detector: magnetic signal strength is thus reduced. As 9 a result, despite its clinical interest, SQUID based magnetocardiography is not widespread in 10 hospitals. 11 12 Several emerging sensors dedicated to the measurements of low magnetic fields have been 13 developed during the past few years (Pannetier-Lecoeur et al., 2011) (Livanov et al., 1981). Among 14 them, cryogenic-free Optically-Pumped Magnetometers (OPM) have emerged as a promising 15 alternative to SQUIDs detector (Knappe et al., 2010). High sensitivity OPMs tested in the past are all 16 based on a vapor of alkali atoms and exploit the optical and magnetic properties of paramagnetic 17 alkali atoms. The most commonly used architectures of alkali OPM in the MCG field are Mx 18 magnetometers (Bison, 2004) and the so-called Spin-Exchange Relaxation-Free (SERF) 19 magnetometers (Wyllie et al., 2012), (Shah and Wakai, 2013). Both of them have only one sensitive 20 axis. MCG mapping has been carried out with an array of 83 Mx magnetometers in a second-order 21 gradiometer configuration: achieved sensitivity is around 1 pT/√Hz in the frequency range 1-10 Hz 22 (Bison et al., 2009) (Bison et al., 2010) (Lembke et al., 2014). Better sensitivities are demonstrated in 23 the SERF regime at the expense of the dynamic range of the sensor (since SERF regime is attained 24 25 only close to zero magnetic field) and higher operating temperature – typically around 150°C which 26 imposes a thermal insulation layer between the sensor and the skin (Xia et al., 2006). In real clinical 27 environment, demonstrated sensitivity of SERF prototypes is comprised between 10-100 fT/√Hz in 28 the frequency range of interest for MCG (0.5-50 Hz). Fetal MCG measurements have recently been 29 performed with an array of these alkali OPMs (Alem et al., 2015) (Wyllie, 2012). 30 In this paper, the possibility to record MCG signals with room-temperature vector OPMs based on 31 helium atoms is demonstrated for the first time. A significant advantage of helium 4 is that it does not 32 require cooling nor heating to be in a gas phase as needed for sensor operation.