An ultrasonic imaging apparatus and method are described for monitoring the progress of therapy for pathology such as lesions, tumors, and metastases by means of contrast agent imaging. A sequence of images are acquired as a bolus of contrast agent infuses the tissue containing the pathology. A contrast wash-in time parameter is calculated for both the tumor and normal tissue, and a ratio is calculated of the two wash-in time parameters (called WITR) which removes the effects of variations in the procedure from one therapy monitoring session to another. A difference curve of the time-intensity curves of the pathology and normal tissue is also produced, which is similarly immune to procedural variations.
