Abstract
In magnetic resonance imaging (MRI), quantitative measurements of analytes are hindered by difficulties in distinguishing the MRI signals of activation of the probe by the analyte from those of the accumulation of the intact probe. Here we show that imaging sensitivity and quantitation can be enhanced by ratiometric MRI probes with a high relaxivity-ratio change (more than 2.5-fold at 7 T) via magnetic-susceptibility-dependent magnetic resonance tuning. Specifically, polymeric probes that incorporate paramagnetic Mn-porphyrin and superparamagnetic iron oxide nanoparticles inducing opposite changes in the longitudinal and transverse magnetic relaxivities responded to analyte concentration independently of probe concentration. In mice, the probes allowed for quantitative real-time dynamic imaging of H2O2, H2S or pH in subcutaneous tumours, in livers with drug-induced injury and in orthotropic gliomas. The ratiometric MRI probes may be advantageously used to obtain molecular insight into pathological processes and to circumvent interference from dynamic changes in probe concentration within the body while providing anatomical information.
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Data availability
The main data supporting the results in this study are available within the paper and its Supplementary Information. All data generated in this study, including source data for the figures, are available in Figshare (https://doi.org/10.6084/m9.figshare.21802755)61. Source data are provided with this paper.
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Acknowledgements
This work was supported by the National Natural Science Foundation of China (grant nos. U21A20287 to G.S. and 22234003 to X.-B.Z.), the National Key R&D Program of China (grant no. 2019YFA0210100 to X.-B.Z.), and the Shenzhen Science and Technology Program (grant no. JCYJ20210324140205013 to G.S.).
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C.Z. synthesized various responsive polymers and Mn-porphyrins. J.X. prepared superparamagnetic iron oxide nanoparticles and Gd2O3 nanoparticles. C.Z. and B.N. completed the test experiment in solution. C.L. performed the TEM experiments and measured field-dependent magnetization hysteresis loops. T.Y. collected spectra data and conducted the MTT assay. L.X. constructed orthotopic glioma tumour models. C.Z., B.N. and J.X. built other animal models and conducted all animal experiments. C.Z. collected raw data in all experiments and designed schematics. G.S. and C.Z. designed all experiments. G.S. conceived the idea for this project. G.S. supervised all experiments. G.S., C.Z. and J.R. analysed all data and interpreted the results. C.Z., G.S. and J.R. co-wrote the manuscript. All authors provided critical feedback on the research and the manuscript.
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Extended data
Extended Data Fig. 1 Merger of mapping images of tumour with corresponding MR images for H+-RMN or Ir-RMN-2.
a, b, Merger of T1 and T2 mapping images of tumour with corresponding T1/ T2-weighted MRI images of 4T1 tumour bearing mice intratumourally injected with H+-RMN or Ir-RMN-2.
Extended Data Fig. 2 The effect of varying volumes of injected buffer on the RMS (r2/ r1) of tumours.
a, Schematic illustration of two groups of 4T1 tumour-bearing mice i.t. injected with H+-RMN, each group with the same mass but different volumes of buffer solution. b, c, Merger of T1/ T2-weighted MRI images and relaxation time mapping for Group 1 - 2, before and 4 h post injection of H+-RMN, respectively. d, e, Quantification of T2 relaxation time (d) and T1 relaxation time (e) of 4T1 tumour bearing mice i.t. injected with different volumes of H+-RMN (Group 1 - 2), measured from (b) and (c). f, RMS (r2/ r1) of tumour for Group 1 - 2, calculated from (d) and (e). For d–f, n = 3 biological replicates. Data are presented as mean ± SD. Statistical analysis was performed using two-tailed Student’s t-tests. n.s: no statistically significant differences (P = 0.622).
Extended Data Fig. 3 Merger of mapping images of tumour with corresponding MR images for H2O2-RMN or Ir-RMN-1.
a, b, Merger of T1 and T2 mapping images of tumour with corresponding T1/ T2-weighted MRI images of 4T1 tumour bearing mice intratumourally injected with H2O2-RMN or Ir-RMN-1.
Extended Data Fig. 4 Ratiometric MRI of H2S in tumour.
a, Merger of representative T1 and T2 mapping images of HCT116 tumour with corresponding T1/ T2-weighted MRI images, before and 6 h post injection of H2S-RMN. b, c, Quantification of T2 relaxation time (b) and T1 relaxation time (c) from (a). d, RMS (r2/ r1) of HCT116 tumour, calculated from (b) and (c). For b–d, n = 3 biological replicates. Data are presented as mean ± SD.
Extended Data Fig. 5 Assessment tissue H2O2 levels between the tumours in living animals and those excised after sacrifice.
a, In vivo fluorescence images of 4T1-tumour-bearing mice intratumourally injected with NIR-H2O2 at different time pointes. b, Ex vivo fluorescence images of isolated tumour tissues intratumourally injected with NIR-H2O2 at different time pointes. c, Normalized fluorescence intensity form (a) and (b), n = 3 biological replicates. Data are presented as mean ± SD. Statistical analysis was performed using two-tailed Student’s t-tests. n.s: no statistically significant differences (P = 0.891 at 40 min, P = 0.877 at 90 min).
Extended Data Fig. 6 Quantification of H2S in tumour via ratiometric MRI.
a, Schematic illustration of quantification H2S concentration in tumour via using the standard curve between H2S concentration and the RMS (r2/ r1) of H2S-RMN. b, Quantification of H2S concentrations in HCT116 tumours for Group 1 - 4 via a commercial H2S kit. c–f, Merger of representative T1 and T2 mapping images of tumour with corresponding T1/ T2-weighted MRI images for Group 1 - 4, before and 6 h post injection of H2S-RMN into mice bearing HCT116 tumours. g, Quantification of T2 relaxation time, measured from (c) - (f). h, RMS (r2/ r1) of tumour for Group 1 - 4, calculated from (g) and Supplementary Fig. 51. i, Correlation between RMS (r2/ r1) of tumour area and H2S concentration of tumour tissue for Group 1 - 4. For b, g–i, n = 3 biological replicates. Data are presented as mean ± SD.
Extended Data Fig. 7 Quantification pH in tumour via ratiometric MRI.
a, Schematic illustration of quantification pH in tumour via using the standard curve between intratumour pH value and the RMS (r2/ r1) of H+-RMN. b, Quantification the pH value of Group 1 - 4, via a microelectrode pH meter. c–f, Representative T1 and T2 mapping images of tumour merged with corresponding T1/ T2-weighted MRI images for Group 1 - 4. g, Quantification of T2 relaxation time, measured from (c) - (f). h, RMS (r2/ r1) of tumour for Group 1 - 4, calculated from (g) and Supplementary Fig. 52. i, Correlation between RMS (r2/ r1) of tumour area and pH value of tumour tissue for Group 1 - 4. For b, g–i, n = 3 biological replicates. Data are presented as mean ± SD.
Extended Data Fig. 8 T2-weighted MRI of drug-induced liver injury.
a, Coronal section of T2-weighted MRI images of representative slice in mice treated with APAP, APAP + H2O2-RMN and saline + H2O2-RMN, respectively. b, Normalized T2-MRI intensity from (a). c, Corresponding quantification of T2-MRI signal for APAP + H2O2-RMN and saline + H2O2-RMN from (a).
Extended Data Fig. 9 Ratiometric MRI of H2O2 during drug-induced liver injury.
a–c, Merger of T1/ T2-weighted MRI images and relaxation time mapping of mice treated with saline + H2O2-RMN, APAP + H2O2-RMN or GSH + APAP + H2O2-RMN over time, respectively.
Extended Data Fig. 10 Ratiometric MRI of orthotopic brain-tumour xenografts in mice.
a, b, T2-weighted MR images, T1 and T2 mapping images of orthotopic brain tumour bearing mice intravenously injected with H2O2-RMN or Ir-RMN-1 over time.
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Zhang, C., Nan, B., Xu, J. et al. Magnetic-susceptibility-dependent ratiometric probes for enhancing quantitative MRI. Nat. Biomed. Eng 9, 671–685 (2025). https://doi.org/10.1038/s41551-024-01286-4
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DOI: https://doi.org/10.1038/s41551-024-01286-4
