The third generation + Fourth generation +  slip ring technology + Helical motion = sixth generation of CT scan. The sixth generation of ct scan design 1990. A slip ring is a circular contact with sliding brushes that allows the gantry to rotate continually. The use of slip-ring technology eliminated the inertial limitations at the end of each slice acquisition, and the rotating gantry was free to rotate continuously throughout the entire patient examination. This design made it possible to achieve greater rotational velocities than with systems not using a slip ring, allowing shorter scan times.  The helical CT scan acquired data while the table is moving. The total Scan time required to image the patient can be much shorter, excluding time required to translate the patient table. It allows the less contrast agent and increases patient through. In some cases the entire scan can be done within a single breath hold of the patient.