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- Chukharkin Leonidovich, Maxim, 1980, et al.
(författare)
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Novel HTS DC squid solutions for NMR applications
- 2014
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Ingår i: NATO Science for Peace and Security Series B: Physics and Biophysics. - Dordrecht : Springer Netherlands. - 1874-6500. - 9789400772649 ; 2014, s. 151-159
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a multilayer flux-transformer-based high-TC SQUID (flip-chip) magnetometer that improves signal-to-noise-ratios (SNR) in ultra-low field magnetic resonance (ulf-MR) recordings of protons in water. Direct ulf-MR-based benchmarking of the flip-chip versus a standard planar high-T C SQUID magnetometer resulted in improvement of the SNR by a factor of 2. This gain is attributable to the improved transformation coefficient (1.9 vs 5.3 nT/Φ0) that increased the signal available to the flip-chip sensor and to the lower noise at the measurement frequency (15 vs 25 fT/Hz1/2 at 4 kHz). The improved SNR can lead to better spectroscopic resolution, lower imaging times, and higher resolution in ulf-MR imaging systems based on high-T C SQUID technology. The experimental details of the sensors, calibration, and ulf-MR benchmarking are presented in this report.
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| 2. |
- Zevenhoven, Koos C J, et al.
(författare)
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Conductive shield for ultra-low-field magnetic resonance imaging: Theory and measurements of eddy currents
- 2014
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 115:10, s. 12-
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Tidskriftsartikel (refereegranskat)abstract
- Eddy currents induced by applied magnetic-field pulses have been a common issue in ultra-low-field magnetic resonance imaging. In particular, a relatively large prepolarizing field-applied before each signal acquisition sequence to increase the signal-induces currents in the walls of the surrounding conductive shielded room. The magnetic-field transient generated by the eddy currents may cause severe image distortions and signal loss, especially with the large prepolarizing coils designed for in vivo imaging. We derive a theory of eddy currents in thin conducting structures and enclosures to provide intuitive understanding and efficient computations. We present detailed measurements of the eddy-current patterns and their time evolution in a previous-generation shielded room. The analysis led to the design and construction of a new shielded room with symmetrically placed 1.6-mm-thick aluminum sheets that were weakly coupled electrically. The currents flowing around the entire room were heavily damped, resulting in a decay time constant of about 6ms for both the measured and computed field transients. The measured eddy-current vector maps were in excellent agreement with predictions based on the theory, suggesting that both the experimental methods and the theory were successful and could be applied to a wide variety of thin conducting structures. (C) 2014 AIP Publishing LLC.
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