Ultrasound is mainly used for the examination of the abdomen and small organs. There are several categories: 1. morphological changes of tissues and organs (common ones are fatty liver, hepatitis, cholecystitis, pancreatitis, splenomegaly, nephritis, hydronephrosis, ureteral dilatation, bladder diverticulum, uterine dysplasia, adnexitis, hyperthyroidism, enlarged lymph nodes, breast hyperplasia, etc.) 2.Measurement of fetal growth and development indicators (biparietal diameter, head circumference, abdominal circumference, femur, humerus, etc.) 3.Localization and quantitative examination of pleural effusion, peritoneal effusion and pericardial effusion (range, maximum depth, fluoroscopy, etc.) 4.Abnormal occupancy of various tissues and organs (cystic, solid, mixed, and complex, etc., while the morphology, size, boundary, internal echogenicity, etc. of the occupancy can be differentially diagnosed.) 5.Other (to assist clinical monitoring of ovulation, bedside examination, etc.) B ultrasound examination is a very important auxiliary clinical examination item, which can be repeated because of its radiation-free and harmless nature. Nowadays, B-ultrasound is mainly used in small clinics or remote areas, but most of the areas in China have been updated to color ultrasound. Although B ultrasound has its own limitations, there are many diseases that can be screened by ultrasound.