Abstract: A submersible apparatus, having at least one aperture formed in the body of the apparatus and one or more sanitizing or disinfecting tablets being contained within the apparatus, is placed into a swimming pool or other body of water. Initially, the combined mass of the apparatus and the chlorine tablets contained within the body of the apparatus will have slightly negative buoyancy and, as the apparatus sinks into the water, the position of the apparatus will stabilize (e.g., reach neutral buoyancy) at a position at or near the bottom of the swimming pool. As the chlorine tablets interact with the water in the swimming pool and slowly dissolve, the buoyancy of the apparatus increases (becomes more positive) and the apparatus gradually rises vertically until it reaches the surface of the swimming pool.

Abstract: A subject (22), such as a human patient, is positioned with a region of interest (24), such as the liver, close proximity to a phantom (12). A Volume image through the liver, the phantom, and adjacent portions of the subject are collected (40) with a magnetic resonance scanner. The phase component of the magnetic resonance data is reconstructed (50) into a three-dimensional phase map. An actually measured field map H.sub.m (r) is determined (42) from the phase map. A geometric model of the volumes occupied by the liver, the phantom, and adjacent portions of the subject are defined mathematically (44). A calculation routine (46) calculates a calculated or estimated field map H.sub.c (r) of the distortions to the magnetic field in the phantom which would be caused by the model.