Monitoring system for the current flow to dual resonant 1H/31P MRI coils
A current sensing system for a magnetic resonance imaging (MRI) scanner operating at 1H and 31P resonant frequencies includes a dual-tuned RF coil with a network of up to two parallel quarter-wavelength transmission lines, each integrated with a PIN diode-coupled shunt capacitor. A multiple half-wavelength transmission line is employed with a corresponding pair of shunt capacitors and PIN diodes. A quarter-wavelength transmission line, coupled with a power amplifier through a matching network of shunt capacitors and PIN diodes, is also included. The configuration parameters are designed to tune the system to the fundamental frequency and its first odd multiple, correlating with the 1H resonant frequency, and to the 31P resonant frequency. The system accurately senses coil currents by detecting voltage variations in the matching network, thereby facilitating precise current measurements at the tuned resonant frequencies without the need for external sensors.
1 . A current sensing system for a 1H/31P magnetic resonance imaging (MRI) scanner, comprising:
a coil network of a dual-tuned radiofrequency (RF) coil, comprising:
up to two parallel transmission lines connected to a transmission antenna of the dual-tuned radiofrequency (RF) coil, wherein each of the up to two parallel transmission lines has a length of quarter-wavelength; and
a pair of first shunt capacitors connected across the up to two parallel transmission lines, wherein each first shunt capacitor of the pair of first shunt capacitors is connected in series with a respective PIN diode;
a transmission line segment, comprising:
a first transmission line having a length of a multiple of half-wavelength; and
a pair of second shunt capacitors connected across the first transmission line, wherein each second shunt capacitor of the pair of second shunt capacitors is connected in series with a respective PIN diode;
a matching network coupled to a power amplifier, comprising:
a second transmission line having a length of a quarter-wavelength; and
a pair of third shunt capacitors connected across the second transmission line, wherein each third shunt capacitor of the pair of third shunt capacitors is connected in series with a respective PIN diode;
wherein the respective length of the first transmission line and the second transmission line are configured to tune the current sensing system to a fundamental frequency and to a first odd multiple frequency of the fundamental frequency, wherein the fundamental frequency is a 31P resonant frequency;
wherein each of the pair of first shunt capacitors, the pair of second shunt capacitors and the pair of third shunt capacitors are configured to tune the current sensing system to a 1H resonant frequency;
wherein each of the respective PIN diodes of the pair of first shunt capacitors, the pair of second shunt capacitors and the pair of third shunt capacitors are configured to set the current sensing system to at least one of the 31P resonant frequency and the 1H resonant frequency; and
wherein the current sensing system is tuned to at least one of the 31P resonant frequency and the 1H resonant frequency, and is configured to sense a current of the dual-tuned radiofrequency (RF) coil network at a respective tuned resonant frequency by sensing a voltage of the matching network coupled to the power amplifier.
2 . The current sensing system of claim 1 , wherein the transmission line segment comprises a plurality of transmission lines, each having a length of a multiple of double quarter-wavelength.
3 . The current sensing system of claim 2 , wherein the transmission line segment comprises a pair of third shunt capacitors connected across each of the plurality of transmission lines resulting in a plurality of pairs of third shunt capacitors, wherein each third shunt capacitor of the plurality of pairs of third shunt capacitors is connected in series with a respective PIN diode.
4 . The current sensing system of claim 1 , wherein the transmission line segment is configured to apply a current forcing technique to the current sensing system.
5 . The current sensing system of claim 1 , wherein the power amplifier is configured to apply a cartesian feedback loop (FBL).
6 . The current sensing system of claim 1 , wherein a value of the first shunt capacitor is 22.5 pF, a value of the second shunt capacitor is 15.7 pF and a value of the third shunt capacitor is 11.3 pF.
7 . The current sensing system of claim 1 , wherein the 31P resonant frequency is 120 MHz.
8 . The current sensing system of claim 1 , wherein the 1H resonant frequency is 298 MHz.
9 . The current sensing system of claim 1 , wherein the coil network is configured to match an input impedance of the dual-tuned radiofrequency (RF) coil to an impedance of the transmission line segment.
10 . A current sensing system for a multi-tuned magnetic resonance imaging (MRI) scanner, comprising:
a coil network of a multi-tuned radiofrequency (RF) coil, comprising:
up to two parallel transmission lines connected to a dipole antenna of the multi-tuned radiofrequency (RF) coil, wherein each of the up to two parallel transmission lines have a length of quarter-wavelength; and
a pair of first shunt capacitors connected across the up to two parallel transmission lines, wherein each first shunt capacitor of the pair of first shunt capacitors is connected in series with a respective PIN diode;
a transmission line segment, comprising:
a first transmission line having a length selected from a multiple of half-wavelength and a multiple of double quarter-wavelength; and
a pair of second shunt capacitors connected across the first transmission line, wherein each second shunt capacitor of the pair of second shunt capacitors is connected in series with a respective PIN diode;
a matching network coupled to a power amplifier, comprising:
a second transmission line having a length of a quarter-wavelength; and
a pair of third shunt capacitors connected across the second transmission line, wherein each third shunt capacitor of the pair of third shunt capacitors is connected in series with a respective PIN diode;
wherein the respective length of the first transmission line and the second transmission line in combination with each of the pair of first shunt capacitors, the pair of second shunt capacitors and the pair of third shunt capacitors are configured to tune the current sensing system to one or more resonant frequencies;
wherein each of the respective PIN diodes of the pair of first shunt capacitors, the pair of second shunt capacitors and the pair of third shunt capacitors are configured to set the current sensing system to at least one of the one or more resonant frequencies; and
wherein the current sensing system is tuned to at least one of the one or more resonant frequencies, and is configured to sense a current of the multi-tuned radiofrequency (RF) coil network at a respective tuned resonant frequency by sensing a voltage of the matching network coupled to the power amplifier.
11 . A method for sensing current of a radiofrequency (RF) coil of a dual-tuned magnetic resonance imaging (MRI) scanner, comprising:
connecting a coil network comprising up to two parallel transmission lines, each with a length of a quarter-wavelength to a dipole antenna of the radiofrequency (RF) coil;
connecting a matching network comprising a transmission line with a length of a quarter-wavelength to a power amplifier of the magnetic resonance imaging (MRI) scanner;
connecting the matching network and the coil network using a transmission line segment with a length of at least one of a multiple of half-wavelength and a multiple of double quarter-wavelength;
tuning the coil network, the matching network, and the transmission line segment to a first resonant frequency of the dual-tuned magnetic resonance imaging (MRI) scanner;
tuning the coil network, the matching network, and the transmission line segment to a second resonant frequency of the dual-tuned magnetic resonance imaging (MRI) scanner using three pairs of shunt capacitors with each pair of shunt capacitors connected across each of the coil network, the matching network, and the transmission line segment;
setting the coil network, the matching network, and the transmission line segment to at least one of the first resonant frequency and the second resonant frequency of the dual-tuned magnetic resonance imaging (MRI) scanner using six PIN diodes, wherein each of the six PIN diodes is connected in series to each of the shunt capacitor of the three pairs of shunt capacitors; and
sensing a current of the radiofrequency (RF) coil of the dual-tuned magnetic resonance imaging (MRI) scanner tuned to at least one of the first resonant frequency or the second resonant frequency by measuring a voltage across the matching network connected to the power amplifier.
12 . The method of claim 11 , further comprising tuning the coil network, the matching network, and the transmission line segment to a fundamental frequency of 120 MHz, wherein the fundamental frequency is the first resonant frequency.
13 . The method of claim 11 , wherein the dual-tuned magnetic resonance imaging (MRI) scanner is a 1H/31P magnetic resonance imaging (MRI) scanner.
14 . The method of claim 11 , wherein the first resonant frequency is a resonant frequency of 31P atomic nuclei (120 MHz) of the dual-tuned magnetic resonance imaging (MRI) scanner.
15 . The method of claim 11 , wherein the second resonant frequency is a resonant frequency of 1H atomic nuclei (298 MHz) of the dual-tuned magnetic resonance imaging (MRI) scanner.
16 . The method of claim 11 , wherein the values of each pair of the three pairs of shunt capacitors is selected from 22.5 pF, 15.7 pF and 11.3 pF.