1. A method for assessing a lesion at a tissue treatment site, comprising: determining a first position and first orientation of a catheter equipped with ultrasound, based on a first signal received from a position sensor disposed on the catheter; collecting a first set of echo data from the catheter equipped with ultrasound at the first position and first orientation, wherein the first set of echo data is associated with the tissue treatment site; determining a second position and second orientation of the catheter equipped with ultrasound, based on a second signal received from the position sensor disposed on the catheter; collecting a second set of echo data from the catheter equipped with ultrasound at the second position and second orientation, wherein the second set of echo data is associated with the tissue treatment site; associating the first and second set of echo data with the tissue treatment site based on the first and second signal received from the position sensor, respectively; determining a first temperature of the tissue treatment site from the first set of echo data and a second temperature of the tissue treatment site from the second set of echo data; and assessing, with a computer, a formation of the lesion based at least in part on a difference between the first and second temperatures exceeding a threshold.