Fig. 3: Millimetre-scale cardiac magnetic field mapping.

a Optical image of the rat’s heart. b, c Measured magnetic field map at the timing of the R-wave peak obtained with the nitrogen-vacancy (NV) centres for \({d}^{{{{{{\rm{NV}}}}}}}=7.5\pm 0.5\) mm and with the optically pumped magnetometer (OPM) for \({d}^{{{{{{\rm{OPM}}}}}}}=14\pm 2\) mm, respectively. The field of view is the same as that of the optical image, with an accuracy of better than 2 mm. The superimposed grey solid line shows the contour of the rat’s heart traced from the magnetic resonance imaging (MRI) (d). d Magnetic resonance image of the rat’s heart, the orientation of which is adjusted to the optical image. The Purkinje fibre bundle is located in the inner ventricular walls between the left and right ventricular. e, f Fitted magnetic field map using the multiple-current-dipole model, superimposed on the contour of the internal structure of the rat’s heart (grey dashed line) revealed by MRI (d). The black arrows represent the location, direction, and relative magnitude of the central dipole. The black dash-dotted circle depicts the localisation precision of the central dipole. The current dipoles are estimated such that the mean squared error between the measured and simulated magnetic fields is minimal.