Magnetocardiography is a contactless imaging modality for electric current propagation in the cardiovascular system. Although conventional sensors provide sufficiently high sensitivity, their spatial resolution is limited to a centimetre-scale, which is inadequate for revealing the intra-cardiac electrodynamics such as rotational waves associated with ventricular arrhythmias. Here, we demonstrate invasive magnetocardiography of living rats at a millimetre-scale using a quantum sensor based on nitrogen-vacancy centres in diamond. The acquired magnetic images indicate that the cardiac signal source is well explained by vertically distributed current dipoles, pointing from the right atrium base via the Purkinje fibre bundle to the left ventricular apex. We also find that this observation is consistent with and complementary to an alternative picture of electric current density distribution calculated with a stream function method. Our technique will enable the study of the origin and progression of various cardiac arrhythmias, including flutter, fibrillation, and tachycardia.

Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation technique that has been clinically applied for neural modulation. Conventional TMS systems are restricted by the trade-off between depth penetration and the focality of the induced electric field. In this study, we integrated the concept of temporal interference (TI) stimulation, which has been demonstrated as a non-invasive deep-brain stimulation method, with magnetic stimulation in a four-coil configuration. The attenuation depth and spread of the electric field were obtained by performing numerical simulation. Consequently, the proposed temporally interfered magnetic stimulation scheme was demonstrated to be capable of stimulating deeper regions of the brain model while maintaining a relatively narrow spread of the electric field, in comparison to conventional TMS systems. These results demonstrate that TI magnetic stimulation could be a potential candidate to recruit brain regions underneath the cortex. Additionally, by controlling the geometry of the coil array, an analogous relationship between the field depth and focality was observed, in the case of the newly proposed method. The major limitations of the methods, however, would be the considerable intensity and frequency of the input current, followed by the frustration in the thermal management of the hardware.

BackgroundSentinel node biopsy using radioisotope and blue dye remains a gold standard for axillary staging in breast cancer patients with low axillary burden. However, limitations in the use of radioisotopes have resulted in emergence of novel techniques. This is the first in vivo study to assess the feasibility of combining the two most common novel techniques of using a magnetic tracer and indocyanine green (ICG) fluorescence.Materials and methodsA total of 48 mice were divided into eight groups. Groups 1 and 2, the co-localization groups, received an injection of magnetic tracers (Resovist® and Sienna+®, respectively) and ICG fluorescence; distilled water was used as the solvent of ICG. Groups 3 and 4, the diluted injection groups, received an injection of magnetic tracers (Resovist and Sienna+, respectively) and saline for dilution. Groups 5, 6, and 7, the control groups, received magnetic tracer (Resovist, Sienna+) and ICG alone, respectively. Fluorescent intensity assessment and iron quantification of excised popliteal lymph nodes were performed. Group 1′, a co-localization group, received an injection of magnetic tracers (Resovist) and ICG′ fluorescence: saline was used as the solvent for ICG.ResultsLymphatic uptake of all tracers was confined to the popliteal nodes only, with co-localization confirmed in all cases and no significant difference in fluorescent intensity or iron content of ex vivo nodes between the groups (except for Group 1′). There was no impact of dilution on the iron content in the diluted Sienna+ group, but it significantly enhanced Resovist uptake (P=0.005). In addition, there was a significant difference in iron content (P=0.003) in Group 1′.ConclusionThe combination of a magnetic tracer (Resovist or Sienna+) and ICG fluorescence is feasible for sentinel node biopsy and will potentially allow for precise transcutaneous node identification, in addition to accurate intraoperative assessment. This radioisotope-free “combined technique” warrants further assessment within a clinical trial.

Purpose: Neuropathic pain is a complex and distressing chronic illness in modern medicine. Since 1990s, motor cortex stimulation (MCS) has emerged as a potential treatment for chronic neuropathic pain; however, the precise mechanisms underlying analgesia induced by MCS are not completely understood. The purpose of the present study was to investigate the blood oxygen-level dependent (BOLD) response in the brain during MCS. Methods: We inserted a bipolar tungsten electrode into the primary motor cortex (M1) of adult male Wistar rats. Functional magnetic resonance imaging (fMRI) scans were implemented simultaneously with the electrical stimulation of M1 and the BOLD signals taken from the fMRI were used as an index to reflect the response against MCS. Results: Our results demonstrated that the bilateral M1, ipsilateral caudate-putamen, and ipsilateral primary somatosensory cortex to the stimulation spot were activated after the onset of MCS. The BOLD signal time courses were analysed in these regions and similar temporal characteristics were found. Conclusion: By conducting direct cortical stimulation of the rodent brain to investigate its instant effect using fMRI, we identified encephalic regions directly involved in the instant motor cortical stimulation effects in healthy rat models. This result may be essential in establishing a foundation for further research on the underlying neuropathways associated with the MCS effects.

Temporal interference stimulation (TIS) is a novel, non-invasive deep brain stimulation (DBS) methodology thatutilizes multiple external electric fields with amplitude modulation (AM) to stimulate deep brain regions without affectingthe superficial cortical areas. However, the clinical application of TIS is inhibited by its unproved response of the brain to the modulated stimulation. In this study, we investigated the instantaneous brain response to TIS using fMRI technique in rodents. The results demonstrated the compatibility of TIS with fMRI, as well as the feasibility of stimulating subcortical encephalic regions non-invasively and focally.