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High-temperature superconducting radiofrequency probe for magnetic resonance imaging applications operated below ambient pressure in a simple liquid-nitrogen cryostat
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10.1063/1.4802947
/content/aip/journal/rsi/84/5/10.1063/1.4802947
http://aip.metastore.ingenta.com/content/aip/journal/rsi/84/5/10.1063/1.4802947

Figures

Image of FIG. 1.
FIG. 1.

Schematic of the experimental setup used to characterize the HTS coil as a function temperature ( ) and applied static magnetic field ( ). The resonance frequency (  ) and the quality factor () of the HTS coil were extracted from the reflection coefficient (ρ) at the output port of an inductively coupled loop probe. was set by controlling the pressure ( ) and temperature ( ) equilibrium in a liquid nitrogen (LN) bath. A pressure instruction ( ) was sent to a pressure regulator with output pressure (P) to control through a vacuum line with a pressure loss Δ. was offset from by temperature gradient Δ along a sapphire cold finger. The cryostat was placed in the fringe field of a MRI magnet bore around 10 m from the electronics.

Image of FIG. 2.
FIG. 2.

The liquid nitrogen cryostat: (a) schematic and (b) secondary vacuum chamber opened with the HTS coil mounted on the sapphire cold finger. Superinsulation layers cover all surfaces of the chamber other than the sapphire window.

Image of FIG. 3.
FIG. 3.

The RF characterization setup with the loop probe coaxially aligned with the HTS coil.

Image of FIG. 4.
FIG. 4.

Resonance frequency (  ) and quality factor () of the HTS coil as a function of the applied magnetic field in parallel and orthogonal orientations without pumping (HTS-coil temperature of 80 K).

Image of FIG. 5.
FIG. 5.

(a) Quality factor () and (b) resonance frequency (  ) of the HTS coil as a function of temperature and applied magnetic field in both parallel or orthogonal orientations.

Image of FIG. 6.
FIG. 6.

(a) Relative improvement of the RF sensitivity ( ) in decibels (dB), as compared to at 80 K in earth's field and (b) detuning effect () with the HTS coil as a function of temperature and applied magnetic field in both parallel or orthogonal orientations. The horizontal dashed lines represent the lower and upper limits of the acceptably tuned domain, corresponding to a –3 dB attenuation of the resonance frequency curve.

Tables

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Table I.

Decline of the HTS coil quality factor in the presence of static magnetic field ( ) reported in the MRI literature involving different HTS coil temperatures ( ) and HTS materials.

Generic image for table
Table II.

Extrapolation of the RF sensitivity ( ) enhancement from 80 K to 66 K in different sample-loading conditions. The effect of the sample was estimated from previous mouse-head and human-skin measurements.

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/content/aip/journal/rsi/84/5/10.1063/1.4802947
2013-05-02
2014-04-20
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: High-temperature superconducting radiofrequency probe for magnetic resonance imaging applications operated below ambient pressure in a simple liquid-nitrogen cryostat
http://aip.metastore.ingenta.com/content/aip/journal/rsi/84/5/10.1063/1.4802947
10.1063/1.4802947
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