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Multimodal imaging—the ability to acquire images of an object through more than one imaging mode simultaneously—has opened additional perspectives in areas ranging from astronomy to medicine. In this paper, we report progress toward combining optical and magnetic resonance (MR) imaging in such a “dual” imaging mode. They are attractive in combination because they offer complementary advantages of resolution and speed, especially in the context of imaging in scattering environments. Our approach relies on a specific material platform, microdiamond particles hosting nitrogen vacancy (NV) defect centers that fluoresce brightly under optical excitation and simultaneously “hyperpolarize” lattice C 13 nuclei, making them bright under MR imaging. We highlight advantages of dual-mode optical and MR imaging in allowing background-free particle imaging and describe regimes in which either mode can enhance the other. Leveraging the fact that the two imaging modes proceed in Fourier-reciprocal domains (real and k-space), we propose a sampling protocol that accelerates image reconstruction in sparse-imaging scenarios. Our work suggests interesting possibilities for the simultaneous optical and low-field MR imaging of targeted diamond nanoparticles. 

Zero- to ultralow-field (ZULF) nuclear magnetic resonance (NMR) is an emerging tool for precision chemical analysis. In this work, we study dynamic processes and investigate the influence of chemical exchange on ZULF NMRJ-spectra. We develop a computational approach that allows quantitative calculation ofJ-spectra in the presence of chemical exchange and apply it to study aqueous solutions of [¹⁵N]ammonium (¹⁵N$${\mathrm{H}}_4^ +$$$H_4^{+}$) as a model system. We show that pH-dependent chemical exchange substantially affects theJ-spectra and, in some cases, can lead to degradation and complete disappearance of the spectral features. To demonstrate potential applications of ZULF NMR for chemistry and biomedicine, we show a ZULF NMR spectrum of [2-¹³C]pyruvic acid hyperpolarized via dissolution dynamic nuclear polarization (dDNP). We foresee applications of affordable and scalable ZULF NMR coupled with hyperpolarization to study chemical exchange phenomena in vivo and in situations where high-field NMR detection is not possible to implement.

 

The purpose of this study was to investigate the feasibility of in vivo¹³C‐>¹H hyperpolarization transfer, which has significant potential advantages for detecting the distribution and metabolism of hyperpolarized¹³C probes in a clinical MRI scanner.

A standalone pulsed¹³C RF transmit channel was developed for operation in conjunction with the standard¹H channel of a clinical 3T MRI scanner. Pulse sequences for¹³C power calibration and polarization transfer were programmed on the external hardware and integrated with a customized water‐suppressed¹H MRS acquisition running in parallel on the scanner. The newly developed RF system was tested in both phantom and in vivo polarization transfer experiments in¹J_CH‐coupled systems: phantom experiments in thermally polarized and hyperpolarized [2‐¹³C]glycerol, and¹H detection of [2‐¹³C]lactate generated from hyperpolarized [2‐¹³C]pyruvate in rat liver in vivo.

Operation of the custom pulsed¹³C RF channel resulted in effective¹³C‐>¹H hyperpolarization transfer, as confirmed by the characteristic antiphase appearance of¹H‐detected,¹J_CH‐coupled doublets. In conjunction with a pulse sequence providing 190‐fold water suppression in vivo,¹H detection of hyperpolarized [2‐¹³C]lactate generated in vivo was achieved in a rat liver slice.

The results show clear feasibility for effective¹³C‐>¹H hyperpolarization transfer in a clinical MRI scanner with customized heteronuclear RF system.