This study presents NMR signal detection by means of a superconducting channel consisting of a Nb surface detection coil inductively coupled to a YBCO mixed sensor. The NMR system operates at a low field (8.9 mT) in a magnetically shielded room suitable for magnetoencephalographic (MEG) recordings. The main field is generated by a compact solenoid and the geometry of the pickup coil has been optimized to provide high spatial sensitivity in the NMR field of view. The Nb detection coil is coupled to the mixed sensor through a Nb input coil. The mixed sensor consists of a superconducting YBCO loop with 2-μm constriction above which two Giant Magneto Resistance sensors are placed in a half-bridge configuration to detect changes of the bridge voltage as a function of the flux through the YBCO loop. The sensitivity of the receiving channel is calibrated experimentally. The measured spatial sensitivity is in agreement with the simulations and is ~10 times better than that of the stand-alone mixed sensor. A NMR echo at 375 kHz shows a SNR only a factor 4 smaller than a tuned room temperature coil tightly wound around the sample, with a noise level which is a factor 3 better than for the volume coil. Our results suggest that mixed sensors are suitable for the integration of low-field MRI and MEG in a hybrid apparatus, where MEG and MRI would be recorded by SQUIDs and mixed sensors, respectively.
2. Trahms, L. and M. Burghoff, "NMR at very low fields," Magnetic Resonance Imaging, Vol. 28, 1244-1250, 2010.
3. McDermott, R., S. Lee, B. T. Haken, A. H. Trabesinger, A. Pines, and J. Clarke, "Microtesla MRI with a superconducting quantum interference device," Proceeding of the National Academy of Sciences of the United States of America, Vol. 101, 7857-7861, 2004.
4. Trabesinger, A. H., R. McDermott, S. Lee, M. Muck, J. Clarke, and A. Pines, "SQUID-detected liquid state NMR in microtesla fields," The Journal of Physical Chemistry A, Vol. 108, 957-963, 2004.
5. Moble, M., S. I. Han, W. R. Myers, S. K. Lee, N. Kelso, M. Hatridge, A. Pines, and J. Clarke, "SQUID-detected microtesla MRI in the presence of metal," Journal of Magnetic Resonance, Vol. 179, 146-151, 2006.
6. Busch, H., M. Hatridge, M. Moble, W. Myers, T. Wong, M. Muck, K. Chew, K. Kuchinsky, J. Simko, and J. Clarke, "Measurements of T1-relaxation in ex vivo prostate tissue at 132 μT," Magnetic Resonance in Medicine, Vol. 67, 1138-1145, 2012.
7. Zotev, V. S., A. N. Matlashov, P. L. Volegov, I. M. Savukov, M. A. Espy, J. C. Mosher, J. J. Gomez, R. H. Kraus Jr., "Microtesla MRI of the human brain combined with MEG," Journal of Magnetic Resonance, Vol. 194, 115-120, 2008.
8. Magnelind, P. E., J. J. Gomez, A. N. Matlashov, T. Owens, J. H. Sandin, P. L. Volegov, and M. A. Espy, "Co-registration of interleaved MEG and ULF-MRI using a 7 channel low-Tc system," IEEE Transactions on Applied Superconductivity, Vol. 21, No. 3, 456-460, 2011.
9. Vesanen, P. T., J. O. Nieminen, K. C. J. Zevenhoven, J. Dabek, L. T. Parkkonen, A. V. Zhdanov, J. Luomahaara, J. Hassel, J. Penttila, J. Simola, A. I. Ahonen, J. P. Makela, and R. J. Il-moniemi, "Hybrid ultra-low-field-MRI and magnetoencephalography system bassed on a commercial whole-head neuromagnetometer," Magnetic Resonance in Medicine, Vol. 69, 1795-1804, 2013.
10. Zotev, V. S., A. N. Matlashov, P. L. Volegov, A. V. Urbaitis, M. A. Espy, and R. H. Kraus Jr., "SQUID-based instrumentation for ultralow-field MRI," Superconductor Science and Technology, Vol. 20, S367-S371, 2007.
11. Bernarding, J., G. Buntkowsky, S. Macholl, S. Hartwig, M. Burghoff, and L. Trahms, "J-coupling nuclear magnetic resonance spectroscopy of liquids in nT fields," Journal of the American Chemical Society, Vol. 128, 714-715, 2006.
12. Hartwig, S., M. Voigt, H. J. Scheer, H. H. Albrecht, M. Burghoff, and L. Trahms, "Nuclear magnetic relaxation in water revisited," The Journal of Chemical Physics, Vol. 135, 054201, 2011.
13. Pannetier-Lecoeur, M., C. Fermon, N. Bizierre, J. Scola, and A. L. Walliang, "RF response of superconducting-GMR mixed sensors, application to NQR," IEEE Transactions on Applied Superconductivity, Vol. 17, No. 2, 598-601, 2007.
14. Sergeeva-Chollet, N., H. Dyvorne, J. Dabek, Q. Herreros, H. Polovy, G. Le Goff, G. Cannies, M. Pannetier-Lecour, and C. Fermon, "Low field MRI with magnetoresistive mixed sensor," Journal of Physics Conference Series, Vol. 303, 012055, 2011.
15. Pannetier, M., C. Fermon, G. Le Goff, J. Simola, and E. Kerr, "Femtotesla magnetic field measurements with magnetoresistive sensors," Science, Vol. 304, 1648-1650, 2004.
16. Pannetier, M., C. Fermon, G. Legoff, J. Simola, E. Kerr, M. Welling, R. J. Wijngaarden, J. Rinke, and , "Ultra-sensitive field sensors --- An alternative to SQUIDs," IEEE Transactions on Applied Superconductivity, Vol. 15, No. 2, 892-895, 2005.
17. Dyvorne, H., J. Scola, C. Fermon, J. F. Jacquinot, and M. Pannetier-Lecoeur, "Flux transformers made of commercial high critical temperature superconducting wires," Review of Scientific Instruments, Vol. 79, 025107, 2008.
18. Grover, F. W., "Inductance Calculations, Working Formulas and Tables," Dover, New York, 1973.
19. Granata, C., A. Vettoliere, S. Rombetto, C. Nappi, M. Russo, "Performances of compact integrated superconducting magnetometers for biomagnetic imaging," Journal of Applied Physics, Vol. 104, 073905, 2008.
20. Rombetto, S., A. Vettoliere, C. Granata, M. Russo, and C. Nappi, "Sensitivity and spatial resolution of square loop SQUID magnetometers," Physica C: Superconductivity, Vol. 468, 2328-2331, 2008.
21. Myers, W., D. Slichter, M. Hatridge, S. Busch, M. Moble, R. McDermott, A. Trabesinger, and J. Clarke, "Calculated signal to noise ratio of MRI detected with SQUIDs and Faraday detectors in fields from 10 ¹T to 1.5 T," Journal of Magnetic Resonance, Vol. 186, 182-192, 2007.
22. Seton, H. C., J. M. S. Hutchison, and D. M. Bussel, "Gradiometer pick-up coil design for a low field SQUID-MRI system," Magnetic Resonance Materials in Physics, Biology and Medicine, Vol. 8, 116-120, 1999.
23. Matlashov, A. N., V. S. Zotev, R. H. Kraus, Jr., H. Sandin, A. V. Urbaitis, P. L. Volegov, and M. A. Espy, "SQUIDs for magnetic resonance imaging at ultra-low magnetic field," PIERS Online, Vol. 5, No. 5, 466-470, 2009.
24. Burghoff, M., H. H. Albrecht, S. Hartwig, I. Hilschenz, R. Korber, T. Sander ThÄommes, H. J. Scheer, J. Voigt, and L. Trahms, "SQUID system for MEG and low field magnetic resonance," Metrology and Measurements Systems, Vol. 16, 371-375, 2009.
25. Nieminen, J. O., P. T. Vesanen, K. C. J. Zevenhoven, J. Dabek, J. Hassel, J. Luomahaara, J. S. Penttila, and R. J. Ilmoniemi, "Avoiding eddy-current problems in ultra-low-field MRI with self-shielded polarizing coils," Journal of Magnetic Resonance, Vol. 212, 154-160, 2011.
26. Hilbert, C., J. Clarke, T. Sleator, and E. L. Hahn, "Nuclear quadrupole resonance detected at 30MHz with a dc supercon-ducting quantum interference device," Applied Physics Letters, Vol. 47, 637-639, 1985.