Millimetre-scale magnetocardiography of living rats with thoracotomy
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-08-23 |
| Journal | Communications Physics |
| Authors | Keigo Arai, Akihiro Kuwahata, Daisuke Nishitani, Ikuya Fujisaki, Ryoma Matsuki |
| Institutions | The University of Tokyo, National Institute for Materials Science |
| Citations | 72 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Millimetre-Scale NV-Diamond Magnetocardiography
Section titled âTechnical Documentation & Analysis: Millimetre-Scale NV-Diamond MagnetocardiographyâThis document analyzes the research detailing millimetre-scale magnetocardiography (MCG) using Nitrogen-Vacancy (NV) centers in Single Crystal Diamond (SCD). This application highlights the critical need for high-purity, high-density SCD material, a core specialty of 6CCVD.
Executive Summary
Section titled âExecutive SummaryâThe research successfully demonstrates invasive, millimetre-scale magnetocardiography (MCG) of living rat hearts using a solid-state quantum sensor based on Nitrogen-Vacancy (NV) centers in diamond.
- High Resolution: Achieved millimetre-scale spatial resolution (5.1 mm current dipole resolution), significantly surpassing the centimetre-scale limitations of conventional sensors (SQUIDs, OPMs).
- High Sensitivity: The NV quantum sensor demonstrated a magnetic field sensitivity of 140 pT Hz-1/2 across the cardiac signal bandwidth (~200 Hz).
- Material Core: The sensor relies on high-density NV centers (~8 x 1016 cm-3) created within a Single Crystal Diamond (SCD) chip, enabling room-temperature operation.
- Short Standoff: The compact, non-cryogenic nature of the diamond sensor allowed for extremely short standoff distances (0.6-2.0 mm from the heart surface), crucial for high-accuracy source identification.
- Advanced Imaging: The technique successfully mapped the spatiotemporal dynamics of cardiac current, revealing vertically distributed current dipoles consistent with Purkinje fibre bundle propagation.
- Clinical Relevance: This methodology provides a pathway for studying the origin and progression of cardiac arrhythmias (flutter, fibrillation) at the necessary millimetre-scale resolution.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the research paper, detailing the performance and material parameters of the NV-diamond quantum sensor system.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Sensor Material | Single Crystal Diamond (SCD) | N/A | NV-center quantum sensor |
| NV Center Density | ~8 x 1016 | cm-3 | High-density electronic spins |
| Magnetic Field Sensitivity | 140 | pT Hz-1/2 | Across cardiac signal bandwidth (~200 Hz) |
| Shot Noise Limit | 19 | pT Hz-1/2 | Theoretical limit |
| Operating Temperature | Room | °C | Key advantage over SQUIDs |
| Standoff Distance (Heart Surface) | 0.6-2.0 | mm | Proximity achieved via thoracotomy |
| Standoff Distance (Heart Center) | 7.5 ± 0.5 | mm | Used for current dipole fitting |
| Dipole Moment Resolution (Aro) | 5.1 | mm | Intra-cardiac scale resolving power (NV sensor) |
| Magnetic Field Resolution (AB) | 1.5 | mm | Limited by imaging pixel size |
| ODMR Linewidth (FWHM) | 2.1 | MHz | Optically Detected Magnetic Resonance |
| Laser Excitation Wavelength | 532 | nm | Green laser source |
| Laser Power (Incident) | 2.0 | W | Used for NV center interrogation |
| Total Dipole Moment (QNV) | (1.3 ± 0.5) x 103 | ”A mm | Fitted from NV data |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relied on precise material engineering and advanced quantum sensing techniques to achieve millimetre-scale resolution MCG.
- Diamond Precursor Selection: The core sensor was a Single Crystal Diamond (SCD) chip, likely grown via MPCVD, which was subsequently processed to create high-density NV centers (~8 x 1016 cm-3).
- NV Center Creation: NV centers were generated via proton irradiation of Type Ib diamond, followed by annealing (implied by standard NV creation protocols).
- Sensor Assembly: The SCD chip was mounted onto a 0.3 mm thick Polycrystalline Diamond (PCD) plate using thermal adhesive. The PCD served as a heat spreader and was attached to an aluminum holder (heat sink/microwave ground plane).
- Optical and Microwave Setup: A 2.0 W, 532 nm green laser was used for excitation at a 70° incidence angle. Triple-frequency microwaves were delivered via a homemade antenna to excite the 14N hyperfine peaks.
- Noise Suppression: Three primary techniques were employed to achieve high sensitivity:
- Low-frequency electronic noise avoidance via lock-in upconverting (fmod = 17-25 kHz).
- Laser fluctuation cancellation using a pick-off laser beam signal subtraction.
- Temperature drift compensation by monitoring double resonance peaks simultaneously.
- Biological Interface: Rats were thoracotomized and the heart was lifted to allow the NV sensor to be placed at a short standoff distance (0.6-2.0 mm) from the heart surface.
- Imaging and Reconstruction: Two-dimensional magnetic field mapping was performed by scanning the rat across 11x11 pixels (1.5 mm step size). Cardiac current density distribution was calculated using a multiple-current-dipole model and a stream-function method.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research validates the critical role of high-quality, engineered diamond materials in next-generation biomedical quantum sensing. 6CCVD is uniquely positioned to supply the necessary diamond substrates and customization services required to replicate, scale, and advance this millimetre-scale MCG technology.
Applicable Materials
Section titled âApplicable MaterialsâThe success of this quantum sensor hinges on the quality and NV density of the diamond. 6CCVD provides the ideal precursor materials:
- Electronic Grade SCD: Our high-purity Single Crystal Diamond wafers are the optimal starting material for creating high-density, high-coherence NV ensembles via irradiation and annealing, matching the ~8 x 1016 cm-3 density reported.
- Optical Grade SCD: For applications requiring superior optical transmission and minimal scattering, 6CCVD offers SCD with guaranteed low birefringence and high transparency at 532 nm and red fluorescence wavelengths.
- PCD Substrates: The paper utilized PCD as a heat spreader. 6CCVD offers large-area Polycrystalline Diamond (PCD) plates up to 125 mm in diameter, providing superior thermal management (critical for handling the 2.0 W laser power) for scaling up sensor arrays.
Customization Potential
Section titled âCustomization PotentialâTo move this technology from the lab bench to integrated devices, custom dimensions, precise polishing, and integrated metalization are essential.
| Research Requirement | 6CCVD Capability | Technical Advantage |
|---|---|---|
| SCD Thickness | SCD (0.1 ”m - 500 ”m) | Allows optimization of NV layer depth relative to the sensor surface for maximum magnetic field coupling. |
| PCD Substrate Size | Plates/wafers up to 125 mm | Enables the development of large-area, high-density sensor arrays for comprehensive cardiac mapping. |
| Surface Quality | Polishing: Ra < 1 nm (SCD) | Guarantees ultra-low roughness necessary for short standoff distances (0.6-2.0 mm) and efficient optical collection. |
| Integrated Circuitry | Custom Metalization (Au, Pt, Ti, Cu) | We can deposit metal stacks directly onto the diamond for integrated microwave antennas, ground planes, and electrical contacts, simplifying sensor packaging. |
| Custom Shapes | Laser Cutting Services | Provides precise shaping and dicing of both SCD and PCD to fit custom sensor heads and probe geometries. |
Engineering Support
Section titled âEngineering SupportâReplicating the reported 140 pT Hz-1/2 sensitivity requires expert knowledge in diamond material science. 6CCVDâs in-house PhD team specializes in CVD diamond growth and post-processing techniques. We can assist researchers in optimizing material selection, surface termination, and NV creation protocols for similar Quantum Sensing and Biomedical Imaging projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract 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.