Real-time 3D CT is a high-speed cone-beam CT (4D-CT) with good low-contrast detectability. In a single rotation, a voxel data set with higher spatial resolution over a wide z- axis range can be obtained. Using continuous rotation, temporarily continuous voxel data sets and 3D dynamic images can be acquired. We have developed a large area 2D detector for 4D-CT, and we have got the first 4D-CT test images.