A magnet keeper-shield assembly adapted to hold and store a permanent magnet used to generate a high gradient magnetic field that, in one embodiment, may penetrate into deep targeted tumor sites in order to attract magnetically responsive micro-carriers. The magnet keeper-shield assembly includes a magnetically permeable keeper-shield with a bore dimensioned to hold the magnet. A lever mechanism is used to push the magnet partially out of the keeper-shield. The actuator is assisted by several springs extending through the base of the keeper-shield.