A system and method is provided for using ultrasound data backscattered from vascular tissue to estimate the transfer function of a catheter and/or substantially synchronizing the acquisition of blood-vessel data to an identifiable portion of heartbeat data. In one embodiment, a computing device and catheter acquire RF backscattered data from a vascular structure. The backscattered ultrasound data is then used to estimate at least one transfer function. The transfer function(s) can then be used to calculate response data for the vascular tissue. Another embodiment includes an IVUS console connected to a catheter and a computing device that acquires RF backscattered data from a vascular structure. Based on the backscattered data, the computing device estimates the catheter's transfer function and to calculate response data for the vascular tissue. The response data and histology data are then used to characterize at least a portion of the vascular tissue.