Usefulness of a method for changing tube current during helical scanning in multislice CT.

Purpose: To determine whether employing a method for changing the tube current during helical scanning helps to adapt the image noise among various sections of the upper abdomen and chest in multislice computed tomography (CT).
Materials and Methods: One hundred CT examinations of the upper abdomen were assigned to one of two scanning protocols: standard scanning with a constant tube current and scanning with the changing method based on protocol 1. One hundred fifty CT examinations of the chest were assigned to one of three protocols: standard scanning with a constant tube current and scanning with the changing method based on protocols 1 and 2. In protocol 1, the tube current for each rotation was reduced in proportion to the water equivalent thickness based on the rotation showing the maximum value, while, in protocol 2, the tube current was increased in proportion to the water equivalent thickness based on the rotation showing the minimum value. The mean tube current, mean standard deviations (SDs) of the measured CT numbers, and dispersion of the SDs were compared between the different protocols.
Results: In the upper abdomen, the use of the changing method based on protocol 1 resulted in a significant reduction in the dispersion of the SDs of CT numbers, with no increase in mean tube current or mean SDs. In the chest, use of the changing method based on protocol 2 resulted in a significant reduction in the dispersion of the SDs of CT numbers, with a reduction in mean tube current and no increase in mean SDs.
Conclusion: The method for changing tube current during helical scanning makes it possible to adapt the image noise among various sections of the upper abdomen and chest without increasing dose in multislice CT.