This paper presents an image reconstruction method for reflective ultrasonic tomography. The variation of the time corresponding to the first peak for the transmitter-receiver pairs is used in the transmission tomography. Commonly, all the reflected packets are used in the reflective reconstruction, but here we assume that the inside of the object is either changing or has a high absorption coefficient. Classical tomography methods are based on an equation where the system matrix is not square. Therefore, inverting such a matrix is a complex task. The solution to this problem is our simple geometrical method, which is very fast and accurate. Moreover, a very high spatial resolution can be achieved. In this case, the amount of information obtained from the system is limited only by the number of transducers used for the ultrasonic measurement.