Automatic measurement of gradient field distortion
AssigneeGeneral Electric Company
InventorsAlexander Ganin, Kevin F. King
Life of this patent
Estimating the term…
Abstract
An MRI system automatically performs a calibration procedure to calculate optimal compensation parameter values for all three gradient pre-emphasis filters. A single fixture is employed to measure the errors caused by gradient pulses produced by each of the three gradient systems. The measured errors are used to calculate a gradient error function and the optimal compensation parameter values are calculated for each pre-emphasis filter by finding the minimum in the gradient error function.
Claims11
An MRI calibration system which comprises:
- a) a fixture mounted in the MRI system at a location in which a polarizing magnetic field and gradient magnetic fields are produced by the MRI system during its operation, the fixture including:
- a first pair of calibration coil assemblies disposed along a first gradient axis;
- a second pair of calibration coil assemblies disposed along a second gradient axis;
- and;
- a third pair of calibration coil assemblies disposed along a third gradient axis;
- wherein each calibration coil assembly includes a calibration coil and a sample material which produces an NMR signal when excited by the MRI system;
- b) a multiplexer having inputs connected to each of the calibration coils and an output coupled to a transceiver on the MRI system;
- and
- the MRI system includes a pulse generator which operates the multiplexer and the MRI system during a calibration procedure to acquire NMR data from each of the calibration coils.
A method for measuring eddy current errors in NMR signals produced by magnetic field gradient pulses in MRI systems, the steps comprising:
- a) mounting a fixture in the MRI system which contains three pairs of calibration coils disposed along three corresponding magnetic field gradient axes of the MRI system;
- b) performing a measurement pulse sequence with the MRI system in which a magnetic field gradient pulse is produced along one of said three axes, an RF excitation pulse is produced a selected time delay after the magnetic field gradient pulse, and NMR signals received by each of said calibration coils are sampled;
- c) repeating step b) at a plurality of different selected time delays;
- and
- d) calculating the eddy current errors from the sampled NMR signals.
Dependencies are inferred from the claim text.