Resistive Magnets

The first whole-body scanners, manufactured in the late 1970s and early 1980s, used four to six large coils of copper or aluminum wire surrounding the patient. These coils are energized by powerful (40–100 kW) direct-current (dc) power supplies. The electrical resistance of the coils leads to substantial joule heating, and the use of cooling water flowing through the coils is necessary to prevent overheating. The heat dissipation increases rapidly with field strength, and it is not feasible to build resistive magnets operating at fields much higher than 0.15–0.3 T. At present, resistive magnets are seldom used except for very low field strength (0.02–0.06 T) applications.