J Korean Soc Magn Reson Med.  2014 Mar;18(1):52-58. 10.13104/jksmrm.2014.18.1.52.

Development of (1)H-(31)P Animal RF Coil for pH Measurement Using a Clinical MR Scanner

• Kim EJ
• Kim D
• Lee S
• Heo D
• Lee YH
• Suh JS

• KMID: 1683780
• DOI: http://doi.org/10.13104/jksmrm.2014.18.1.52

Abstract

PURPOSE
To establish a pH measurement system for a mouse tumor study using a clinical scanner, to develop the (1)H and (31)P radio frequency (RF) coil system and to test pH accuracy with phantoms.
MATERIALS AND METHODS
The (1)H and the (31)P surface coils were designed to acquire signals from mouse tumors. Two coils were positioned orthogonally for geometric decoupling. The pH values of various pH phantoms were calculated using the (1)H decoupled (31)P MR spectrum with the Henderson-Hasselbalch equation. The calculated pH value was compared to that of a pH meter.
RESULTS
The mutual coil coupling was shown in a standard S12. Coil coupling (S12) were -73.0 and -62.3 dB respectively. The signal-to-noise ratio (SNR) obtained from the homogeneous phantom (1)H image was greater than 300. The high resolution in vivo mice images were acquired using a (31)P-decoupled (1)H coil. The pH values calculated from the (1)H-decoupled (31)P spectrum correlated well with the values measured by pH meter (R(2)=0.97).
CONCLUSION
Accurate pH values can be acquired using a (1)H-decoupled (31)P RF coil with a clinical scanner. This two-surface coil system could be applied to other nuclear MRS or MRI.

Keyword

pH; 1H-31P MR coil; mouse; clinical MR

MeSH Terms

Animals*
Hydrogen-Ion Concentration*
Magnetic Resonance Imaging
Mice
Signal-To-Noise Ratio

Figure

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  Fig. 1 The set-up of 1H and 31P RF coils. The two RF coil planes were located orthogonally for geometric decoupling (a). Photo of a 1H receive-only coil (b) and a 31P transmit-and-receive coil (c).

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  Fig. 2 The 1H receive-only coil scheme. Active decoupling consists of a PIN diode switching design and passive decoupling with crossed high-speed switching diodes and a detuning inductor.

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  Fig. 3 The 1H spin-echo images of a homogeneous phantom: (a, b) axial images (TR/TE =167/15 ms, FOV 6 × 6 cm2, 256 × 256), (c, d) coronal images (TR/TE = 150/15 ms, FOV 8 × 8 cm2, 256 × 256). The SNR was measured at ROI (gray ellipse) in (a) and (c).

• 

  Fig. 4 The T2 weighted in vivo mouse images acquired from a 1H receive-only coil with a Fast Recovery Fast Spin-Echo pulse sequence. The parameters of these images were TR=3500 ms, TE=89.3 (coronal)/88.4 (axial) ms, thickness 4 mm, FOV 12 × 12 cm2, matrix 256 × 256 (coronal), 256 × 224 (axial) 2 NEX. One segment of the scale bar denotes 10 mm. The two white bars show the positions of the 1H and 31P RF coils.

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  Fig. 5 (a) 31P MR spectra of the phosphorus phantom. The pH determined by 31P MRS was 7.6 for the upper spectrum and 7.03 for the lower spectrum. (b) Comparison of pH values determined by 31P MRS and pH meter.

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