Design of quadrature-compensated double-tuned RF
A study of NOE enhancement in a double-tuned coil at 3T
31P
MRS with respect to
1H
coil quality and size in
C.-H. Choi ([email protected]), Y. Ha, P. Chervakov, N.J. Shah Institute of Neuroscience and Medicine - 4, Forschungszentrum Jülich, Germany
Results
Introduction
All the 31P data were acquired with an FID sequence with/without NOE (TR/TE=15s/0.35ms, 8 avg., 5kHz BW and for NOE, ten 90ms 180º rectangular pulses with 100ms interval) and processed using jMRUI [5].
31P signals can be boosted with 1H-decoupled or nuclear Overhauser effect (NOE) [1,2]. Different double-tuned coils have been designed with a minimum 31P coil sensitivity loss [3,4].
Table 1 summaries the Q-factors of the probe measured on the bench with various forward currents and shows the Q-factor of the coil increases with increasing the forward current on the PIN-diodes. The NOE enhancement also appears to be related to the Q-factor of the 1H coil.
However, evaluating NOE using double-tuned coils particularly associated with the 1H coil has not been seriously considered. In this study, we designed double-tuned 1H/31P coils and evaluated the NOE effect as a function of the quality/size of the 1H coils.
Ratio of 31P signal enhancement obtained by larger 1H coil was found to be concomitantly higher (Table 1). An example of 31P peaks using Coil (A) with 100 mA with and without NOE enhancement is shown in Fig. 2. The Q-factor of 31P coils remains constant and is not affected by changing the level of the forward current of 1H coil.
Methods
Mitglied der Helmholtz-Gemeinschaft
Fig. 1: Double-tuned 1H/31P coil photographs and schematic diagrams – Coil (A) with PINdiodes, Coil (B) without PIN-diodes and Coil (C) with a larger 1H loop.
Table 1. Q-factors (unloaded/loaded/ratio) of the 1H coils and corresponding NOE enhancement values calculated using 31P data with NOE pulses divided by that without NOE pulses.
comparison data
The double-resonant coils consist of concentrically configured inner (for 31P) and outer (for 1H) loops (Fig. 1). The inner coil includes a trap to isolate coupling at the 1H frequency. Two sets of experiments - quality and/or size dependence - were performed at 3T using a 30mM KH2PO4 phantom. To vary the quality of the coil, we deliberately inserted two PIN-diodes on the outer 1H loop in (Fig. 1) Coil (A), since the applied forward current adjusts the resistance of the PIN-diodes, and therefore affects the quality of the 1H coil. In addition, the effect on NOE enhancement using two different sizes of the 1H coil has been compared. The loop size of Coil (C) is ~33% larger than that of Coil (B) in Fig. 1.
Fig. 2: One of the 31P peaks obtained using the Coil (A) 100 mA with/without employing the NOE enhancement technique.
Discussion/Conclusions The quality/size of the 1H coil may play an important role in contributing to 31P signal enhancement. When designing double-tuned coils, a 1H coil is often sacrificed to minimise the loss at X-nuclei. This work provides an excellent reference for coil builders to optimise their design of double-tuned coils for NOE enhancement.
References
1. Lagemaat NMR Biomed. 2016, 2. van Uden ISMRM 2017, 3. Brown Neuroimage 2016, 4. Schaller ISMRM 2016, 5. Stefan Meas. Sci. Tech. 2009.
31P
MRS with respect to
1H
coil quality and size in
C.-H. Choi ([email protected]), Y. Ha, P. Chervakov, N.J. Shah Institute of Neuroscience and Medicine - 4, Forschungszentrum Jülich, Germany
Results
Introduction
All the 31P data were acquired with an FID sequence with/without NOE (TR/TE=15s/0.35ms, 8 avg., 5kHz BW and for NOE, ten 90ms 180º rectangular pulses with 100ms interval) and processed using jMRUI [5].
31P signals can be boosted with 1H-decoupled or nuclear Overhauser effect (NOE) [1,2]. Different double-tuned coils have been designed with a minimum 31P coil sensitivity loss [3,4].
Table 1 summaries the Q-factors of the probe measured on the bench with various forward currents and shows the Q-factor of the coil increases with increasing the forward current on the PIN-diodes. The NOE enhancement also appears to be related to the Q-factor of the 1H coil.
However, evaluating NOE using double-tuned coils particularly associated with the 1H coil has not been seriously considered. In this study, we designed double-tuned 1H/31P coils and evaluated the NOE effect as a function of the quality/size of the 1H coils.
Ratio of 31P signal enhancement obtained by larger 1H coil was found to be concomitantly higher (Table 1). An example of 31P peaks using Coil (A) with 100 mA with and without NOE enhancement is shown in Fig. 2. The Q-factor of 31P coils remains constant and is not affected by changing the level of the forward current of 1H coil.
Methods
Mitglied der Helmholtz-Gemeinschaft
Fig. 1: Double-tuned 1H/31P coil photographs and schematic diagrams – Coil (A) with PINdiodes, Coil (B) without PIN-diodes and Coil (C) with a larger 1H loop.
Table 1. Q-factors (unloaded/loaded/ratio) of the 1H coils and corresponding NOE enhancement values calculated using 31P data with NOE pulses divided by that without NOE pulses.
comparison data
The double-resonant coils consist of concentrically configured inner (for 31P) and outer (for 1H) loops (Fig. 1). The inner coil includes a trap to isolate coupling at the 1H frequency. Two sets of experiments - quality and/or size dependence - were performed at 3T using a 30mM KH2PO4 phantom. To vary the quality of the coil, we deliberately inserted two PIN-diodes on the outer 1H loop in (Fig. 1) Coil (A), since the applied forward current adjusts the resistance of the PIN-diodes, and therefore affects the quality of the 1H coil. In addition, the effect on NOE enhancement using two different sizes of the 1H coil has been compared. The loop size of Coil (C) is ~33% larger than that of Coil (B) in Fig. 1.
Fig. 2: One of the 31P peaks obtained using the Coil (A) 100 mA with/without employing the NOE enhancement technique.
Discussion/Conclusions The quality/size of the 1H coil may play an important role in contributing to 31P signal enhancement. When designing double-tuned coils, a 1H coil is often sacrificed to minimise the loss at X-nuclei. This work provides an excellent reference for coil builders to optimise their design of double-tuned coils for NOE enhancement.
References
1. Lagemaat NMR Biomed. 2016, 2. van Uden ISMRM 2017, 3. Brown Neuroimage 2016, 4. Schaller ISMRM 2016, 5. Stefan Meas. Sci. Tech. 2009.
