2. Study activities and population group. The study population will be a convenience sample of patients 18 years and younger with suspected appendicitis, whose clinical care (unrelated to the study) includes ultrasound and/or CT of the abdomen. The study intervention includes acquisition of research ultrasound images, which will not be used for clinical care, and comparison of these images with clinically obtained images. Other clinical data such as surgical and pathology reports will also be reviewed. If not evident from the patient medical record, the final diagnosis will be confirmed by a telephone call to the subject 2 weeks after the initial visit.