The invention provides a method for monitoring or predicting the onset or progression of a disease or pathological condition and/or a response to treatment in an infant vertebrate animal subject, wherein said method uses unfocused ultrasound pulses to determine a characteristic of blood flow within the brain of the subject and said characteristic or the profile of said characteristic over time is indicative or predictive of the disease or pathological condition or response to treatment, or variation in said characteristic or the profile of said characteristic over time is indicative or predictive of the disease or pathological condition, or indicative or predictive of a change in the disease or pathological condition or response to treatment.