Inductive measurement of magnetic field gradients for magnetic resonance imaging

Abstract

A simple device for highly accurate and real-time measurement of magnetic field gradient pulses is presented. It uses analog integration of the differential voltage induced in a pair of sensor coils placed along the investigated gradient direction. By this principle, the method is insensitive to static magnetic field inhomogeneities. It does not need either a main field or imaging apparatus and hence can be used in the process of gradient system design and optimization. Two different solutions for analog integration are suggested. The measurement accuracy is analyzed, taking into account errors due to the sensor coils and to both analog integration schemes. Sensor coils and integrators have been built to perform measurements on various gradient systems. Measurements of an actual whole-body gradient system are presented. The measurement accuracy is in the 5–10−4 range, and the reproducibility is better than 10−4, relative to the maximum gradient amplitude. These performances are better than any other presented in literature. They have allowed precise adjustment of a preemphasis unit so as to suppress eddy currents influence below 0.01%, and placed into evidence the thermal drift of standard power amplifier.