Question: when was ultrasound first used for medical purposes
[{'answer': '1941', 'provenance': [{'wikipedia_id': '143357', 'title': 'Medical ultrasound', 'start_paragraph_id': 182, 'start_character': 342, 'end_paragraph_id': 182, 'end_character': 346, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}, {'provenance': [{'wikipedia_id': '143357', 'title': 'Medical ultrasound', 'start_paragraph_id': 182, 'start_character': 10, 'end_paragraph_id': 182, 'end_character': 1390, 'bleu_score': 0.8355752865108991, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15952813415566642585}, 'section': 'Section::::History.\n'}]}]