title: Limits on the measurement of activity level in children using ultrasound and photoelectric cells.
mesh_terms: D002648:Child; D004582:Electronics, Medical; D005069:Evaluation Studies as Topic; D006801:Humans; D006948:Hyperkinesis / Q000175:diagnosis; D008607:Intellectual Disability; D008027:Light; D008722:Methods; D009043:Motor Activity; D012666:Semiconductors; D014159:Transducers; D014465:Ultrasonics / Q000295:instrumentation*