A microwave-based computed tomography system was developed based on a method that uses time domain measurement to determine the shortest path of propagation components between two antennas. The method calculates shortest path of propagation components by examining mixer output DC components, delivering similar precision as chirp-pulse microwave computed tomography. Because post-mixer signal processing need only concerns DC currents, the effects of overshoot characteristics of baseband filters and the like are removed, simplifying measurement. System circuit composition is also simplified, lowering system costs. This paper provides a theoretical framework for the method, an S-parameter verification of the theory, and an experimental verification using a basic hardware construction. Results showed a restored image from the measurement data, indicating the utility of the method for microwave imaging.