Using complementary reconstruction, images from short time frames may be generated for positron emission tomography. Detected events are gathered over a long period, such as three minutes. The detected events from a short period, such as one or two seconds, are removed. Reconstruction is performed on the detected events from the long period and another reconstruction is performed on the detected events from the long period without the detected events from the short period. The second reconstruction is subtracted from the first, providing data representing the short period. The data may result in better image quality than merely reconstructing an individual frame for the short period.