The situation is analogous to what happens when a CT machine malfunctions. The basic design of a CT machine has an x-ray source on a rotating ring. The patien

The situation is analogous to what happens when a CT machine malfunctions. The basic design of a CT machine has an x-ray source on a rotating ring. The patient lays down on a table and the table is moved through the center of the ring at constant velocity for the duration of the scan. The overall motion of the x-ray source relative to the patient is helical. If the movement mechanism jams and the table stops moving, the pattern of motion collapses into a circle and the patient receives an excessive radiation dose focused in the region of the body that is in the center of the ring when the table stops. The received dose is a function of the time until the operator notices the malfunction and stops the scan. With a backscatter x-ray system, the person stays motionless and the x-ray source moves. If the x-ray source stops moving, the person receives an excessive dose wherever the source happens to be pointing when it gets stuck. The dose received is, again, a function of how long it takes for the operator to notice the malfunction. With a microwave backscatter system, the radiation used is in the RF range and, therefore, not ionizing. However, if the microwave source stops moving because of malfunction, a portion of the body experiences higher than normal SAR. If the SAR is high enough, significant localized heating may occur, causing burns on the person.