An ultrasound imaging system is programmed to acquire first ultrasonic image frames intermittently. These first frames, typically triggered frames synchronized with a selected portion of an ECG cycle, are optimized for high image quality of a contrast agent included in the tissue. The imaging system automatically acquires second ultrasonic image frames between at least some of the first frames. The second image frames are typically locator frames which are optimized for reduced degradation of the contrast agent. More of the second frames are acquired per unit time than first frames, and both the first and second frames are displayed, either superimposed over one another or in side-by-side relationship. In this way the user is provided with substantially continuous transducer locating information, yet contrast agent destruction between acquisitions of the first, triggered frames is reduced or eliminated.