Field-frequency lock system for magnetic resonance system
AssigneeGeneral Electric Company
InventorRalph E. Hurd
Life of this patent
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Abstract
A field-frequency lock system for an MRI system includes a microcoil and resonant sample located to sense changes in the polarizing magnetic field. Changes are detected as a shift in frequency of the NMR signal produced by the resonant sample, and the frequency shift is used to compensate the MRI system. Compensation is achieved by adjusting the RF reference signal employed in the MRI system transceiver.
Claims12
In an MRI system having a magnet for producing a polarizing magnetic field B0 in a region, and a gradient coil assembly for producing magnetic field gradients in a subject to be imaged located in the region, a field-frequency lock system which comprises:
- a microcoil located outside the gradient coil assembly and in the region in which the polarizing magnetic field B0 is produced;
- a resonant sample disposed adjacent the microcoil and containing a material that produces a signal when the microcoil is energized with an rf pulse;
- transmit means for producing an rf pulse that is applied to the microcoil;
- receive means for acquiring a signal from the microcoil that is produced by the resonant sample material;
- a frequency comparator for measuring the difference frequency (Δω) between the frequency of the acquired signal and a reference frequency which corresponds to a frequency produced by the resonant sample material when the polarizing magnetic field B0 is at a nominal value;
- and
- means responsive to the difference frequency Δω for compensating the operation of the MRI system as it performs a scan on the subject for variations in the magnitude of the polarizing magnetic field B0.
A method for compensating an MRI system for changes in the polarizing magnetic field of the MRI system, the steps comprising:
- monitoring a microcoil positioned in the polarizing magnetic field at a location in which magnetic field gradients are minimal;
- acquiring an NMR signal from a resonant sample disposed adjacent the microcoil;
- producing a difference signal by comparing the frequency of the acquired NMR signal with the frequency of a reference signal that is indicative of the NMR signal produced by the resonant sample when the polarizing magnetic field has a nominal value;
- and
- producing a compensating signal for the MRI system from the difference signal which offsets changes in the polarizing magnetic field.
Dependencies are inferred from the claim text.