Anti-interference filter for a gradient coil in a nuclear magnetic resonance imaging apparatus

In a magnetic resonance imaging apparatus having a gradient coil with a forward feed line and a return line, said apparatus having an operating frequency, the improvement comprising:

• a pair of anti-interference filters for radio-shielding said forward feed line and said return line respectively connected in said forward feed line and said return line, each anti-interference filter being a band elimination filter which rejects signals at said operating frequency of said apparatus, each of said anti-interference filters containing a plurality of blocking circuits and each blocking circuit having a blocking circuit coil, said anti-interference filters being disposed in a shielded housing spaced from each other with said blocking circuit coils of said anti-interference filters coinciding, each anti-interference filter having a direct current direction therein with the respective direct current directions in said anti-interference filters being opposite for substantially cancelling the respective magnetic fields in said shielded housing produced by the direct currents in said anti-interference filters.

In a magnetic resonance imaging apparatus having three gradient coils each having a forward feed line and a return line associated therewith, said apparatus having an operating frequency, the improvement comprising:

• an anti-interference filter combination for radio-shielding said forward feed lines and said return lines of said gradient coils formed by six anti-interference filters respectively connected in said forward feed lines and said return lines of said three gradient coils, said six anti-interference filters being contained in a shielded housing and each anti-interference filter being a band elimination filter which rejects signals at said operating frequency of said apparatus.