The AccuVein vein illumination device uses two moving mirrors to create its projection. These mirrors take the single laser spot and make the projection rectangle you’re familiar with. The laser is only pointing at one spot at any given time, but since it moves so fast, your eye sees it as a rectangle. Since the AccuVein uses small magnets to move the mirrors, care needs to be taken when using the AccuVein in very close proximity to MRI machines.
The specific rules regarding the use of the AccuVein AV400 near MRIs is that it is acceptable to have the AV400 in zone 1-3 below. But the AV400 should be kept away from zone 4; MRI institution rules would not permit an AV400 into Zone 4 anyway, as it contains ferromagnetic material.