Previous work has shown that hyperpolarized [1,4-13C2]fumarate is a probe of cellular necrosis. We demonstrate here that the ratio of cardiac hyperpolarized malate to fumarate is increased by a factor of ∼82 one day after cryoinduced myocardial infarction in rats, decreasing to an ∼30-fold increase one week after injury. We additionally image this injury with a novel spiral multiband pulse sequence. Hyperpolarized fumarate therefore forms a sensitive probe of myocardial injury in vivo, and could form a clinical monitor of cellular damage and necrosis after infarction.
Hyperpolarization: [1,4-13C2]fumaric acid (3.23mmol; Cambridge Isotopes) was dissolved in 8.74mmol of DMSO containing 11.48μmol of a trityl radical (AH111501; GE Healthcare) and 0.48μmol of a gadolinium chelate (Dotarem, Guerbet). A 40mg aliquot was polarized per experiment (prototype hyperpolarizer, 45min at 94GHz) before dissolution (in 6ml NaOH, final concentration 20mM). Infusion (2ml) was via a tail vein cannula over 20s following dissolution
Myocardial Infarction: Six female Wistar rats (∼200g, Harlan) were divided into two groups (MI or control, n=3), and subject to cryoinduced myocardial infarction.[4] Control animals were subject only to pericardial removal. Pre-operative and postoperative analgesia was provided. All experiments were performed with appropriate ethical review.
Spectroscopy: An actively detuned transmit/surface receive coil was used (72 mm 1H/13C proton/carbon birdcage transmit with 40mm two-channel 13C surface receive; Rapid Biomedical GMBH, Rimpar, Germany) as described previously.[5] A 5M 13C-urea phantom was included as a per-animal FA and frequency reference. Slice-selective spectra (200μs gauss, 20mm thick, TR=∼1s, bandwidth 10kHz, FA 10∘) were acquired from the heart in end-systole. Cardiac function was assessed by CINE.[6] Spectra were summed for 60s following the appearance of the [1,4-13C2]fumarate peak, and quantified with AMARES, with the reported malate:fumarate ratio being that of total visible malate to fumarate.
Multiband Imaging: A hybrid multiband spatial-spectral RF excitation pulse[7] was designed to simultaneously excite [1,4-13C2]fumarate at a 4∘ FA, and both [1,4-13C2]malate resonances at ∼20∘, and a slab thickness of 20mm. A multi-echo spiral readout[8] was constructed to maximise the effective number of signal averages over all chemical species in the subsequent reconstruction, with FID acquisition every seventh echo (TE=2.1,3.8,5.5,7.2,8.9,10.6,12.3 FID 2.1ms). The spiral trajectory was designed with a nominal FOV of 80×80mm2, readout bandwidth of 250kHz, TR=1RR interval, nominal acquisition in-plane resolution 2×2mm2. The pulse sequence is shown in Fig. 1. The k-space trajectory was predicted using a premeasured gradient impulse response function.[9] The multiecho reconstruction was performed prior to NUFFT[10] (30Hz Lorentzian filtered; reconstructed resolution 5.62×5.62mm2; nominal 128×128 matrix). n=1 control and infarcted animals were scanned; other details as above.
The authors would like thank financial support from an EPSRC Doctoral Training Centre Grant and Doctoral Prize Fellowship (refs. EP/J013250/1 and EP/M508111/1) and St. Hugh's College, Oxford. We also acknowledge financial support from the British Heart Foundation (Fellowships FS/10/002/28078 & FS/11/50/29038, Programme Grant RG/11/9/28921).
[1] P. G. Masci, J. Bogaert, Cardiovasc. Diagn. Ther. 2012, 2, 113–27.
[2] F. A. Gallagher, M. I. Kettunen, D.-E. Hu, P. R. Jensen, R. I. ’. Zandt, M. Karlsson, A. Gisselsson, S. K. Nelson, T. H. Witney, S. E. Bohndiek, G. Hansson, T. Peitersen, M. H. Lerche, K. M. Brindle, Proc. Natl. Acad. Sci. U. S. A. 2009, 106, 19801–19806.
[3] M. R. Clatworthy, M. I. Kettunen, D.-E. Hu, R. J. Mathews, T. H. Witney, B. W. C. Kennedy, S. E. Bohndiek, F. A. Gallagher, L. B. Jarvis, K. G. C. Smith, K. M. Brindle, Proc. Natl. Acad. Sci. U. S. A. Aug. 2012, 109, 13374–13379.
[4] E. J. van den Bos, B. M. Mees, M. C. de Waard, R. de Crom, D. J. Duncker, Am J Physiol Hear. Circ Physiol 2005, 289, H1291–300.
[5] J. J. Miller, A. Z. Lau, I. Teh, J. E. Schneider, P. Kinchesh, S. Smart, V. Ball, N. R. Sibson, D. J. Tyler, Magn. Reson. Med. May 2015, 75, 1515–1524.
[6] J. E. Schneider, P. J. Cassidy, C. Lygate, D. J. Tyler, F. Wiesmann, S. M. Grieve, K. Hulbert, K. Clarke, S. Neubauer, J. Magn. Reson. Imaging Dec. 2003, 18, 691–701.
[7] A. Sigfridsson, K. Weiss, L. Wissmann, J. Busch, M. Krajewski, M. Batel, G. Batsios, M. Ernst, S. Kozerke, Magn. Reson. Med. May 2014, DOI 10.1002/mrm.25294.
[8] F. Wiesinger, E. Weidl, M. I. Menzel, M. A. Janich, O. Khegai, S. J. Glaser, A. Haase, M. Schwaiger, R. F. Schulte, Magn. Reson. Med. July 2012, 68, 8–16.
[9] J. H. Duyn, Y. Yang, J. A. Frank, J. W. van der Veen, J. Magn. Reson. May 1998, 132, 150–3.
[10] J. Fessler, B. Sutton, IEEE Trans. Signal Process. Feb. 2003, 51, 560–574.