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Characterizing longitudinal and transverse relaxation rates of ferrofluids in microtesla magnetic fields
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10.1063/1.3671420
/content/aip/journal/jap/110/12/10.1063/1.3671420
http://aip.metastore.ingenta.com/content/aip/journal/jap/110/12/10.1063/1.3671420
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Figures

Image of FIG. 1.
FIG. 1.

(Color online) (a) An NMR apparatus for NMR experiments at low fields; (b) pulse sequences used in NMR measurements.

Image of FIG. 2.
FIG. 2.

(Color online) Time evolution of magnetization M using NMR sequences. (a) The direction of M, Bp , and B0 in the z-direction; (b) The M is in the z-direction; (c) A 90°-pulse rotates the M to the x-direction; (d) the M precesses along the B0 after the 90° pulse is turned off; (e) the M relaxes along the direction of B0 (z-direction); (f) A 180°-pulse rotates the M from the positive z-direction to the negative z-direction; and (g) The M precesses around the B0 and the spin-echo NMR signal is observed.

Image of FIG. 3.
FIG. 3.

(Color online) Geometries of (a) a square-coil pair for generating Gz with the applying current flowing in opposite direction, (b) four rectangular coils for generating Gx, and (c) a complete coil configuration for Gz and Gx.

Image of FIG. 4.
FIG. 4.

(Color online) Spectral linewidth Δf as a function of the proton’s resonance frequency f varying from 1.7 to 9 kHz.

Image of FIG. 5.
FIG. 5.

(Color online) (a) Multi-echo NMR signal of ferrofluids with χ of 1.5 × 10−4 emu/g in a single measurement, (b) the peak strength of multi-echo signals follows the formula S = S0exp(−t/T2) with T2 = 1.797 s, and (c) 1/T2 as a function of χ of ferrofluids in units of emu/g.

Image of FIG. 6.
FIG. 6.

(Color online) Sequences used in the NMR/MRI detection (a) a measuring field B0, z, (b) the pre-polarizing field Bp.y with a duration time TBp, (c) field gradients Gx and Gz applied for the frequency encoding, and (d) FID and gradient-echo NMR signals.

Image of FIG. 7.
FIG. 7.

(Color online) (a) The NMR intensity as a function of TBp for magnetic fluids with different magnetic susceptibilities; (b) 1/T1 as a function of χ of ferrofluids in units of emu/g.

Image of FIG. 8.
FIG. 8.

(Color online) (a) Top view of a phantom with its central part filled with magnetic fluid containing SPIO while the outer part is filled with tap water, (b) NMR intensity as a function of the pre-polarizing time TBp for magnetic fluid and tap water. The dashed lines are guides to the eyes.

Image of FIG. 9.
FIG. 9.

(Color online) High-Tc SQUID-detected MRI for a phantom shown in Figure 8(a) with (a) TBp = 0.3 s, (b) TBp = 1 s, and (c) TBp = 2.5 s.

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/content/aip/journal/jap/110/12/10.1063/1.3671420
2011-12-23
2014-04-16
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Characterizing longitudinal and transverse relaxation rates of ferrofluids in microtesla magnetic fields
http://aip.metastore.ingenta.com/content/aip/journal/jap/110/12/10.1063/1.3671420
10.1063/1.3671420
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