Quantitative image artifacts. Both RFID tags shown on the top have been placed one after the other in the middle of the plastic grid, immersed in 1 g/L CuSO4 solution. Gradient echo and Spin echo sequences as described in the ASTM Standard F2119-01 have been performed. The upper row shows MR images of a 3 mm-thick slice through the tags, the middle row slices 5 mm below the tag and the last row shows an orthogonal slice through the tag. Signal void could be found only a few millimeters away from the tag. Reduced signal due to shielding of the RF field may produce darker shadows in slices up to 1 cm away.