When using Veterinary Ultrasound to examine the uterus of a female dog, it is difficult to visualize the immature uterus using veterinary ultrasound probes below 7.5 MHz. The size of the uterus increases with the age of the animal when it is not pregnant or in estrus, and a full bladder facilitates ultrasound examination of the uterus. Through the acoustic window formed by the bladder, the image of the uterine body is displayed on the ventral side of the rectum. In some cases, the uterus may be displaced and located on the side of the bladder. Using a high-resolution and appropriate frequency veterinary ultrasound probe, the image of the uterine horns can be displayed on the lateral or dorsal side of the distal bladder. Uterine horns can occasionally be seen by veterinary ultrasound scanning along the abdominal wall behind both kidneys. The spleen can also be used as an acoustic window to examine the left uterine horn. Display of the uterine bifurcation helps to examine the uterine horns, usually tracing the uterine body forward until the bifurcation of the uterine horns. The layers of the uterine wall are usually not clearly displayed. The echogenic structure of the uterine wall is usually moderately echogenic to hypoechoic. During estrus, the echogenicity of the uterine wall is weakened due to edema of the uterine body and uterine horns, making it easier to display. The transition from normal morphology to pathological state of the uterus is usually not obvious.

Pyometra in female dogs usually occurs about one month after estrus and mating. As long as it lasts for more than 24 days, veterinary B-ultrasound can be used to clearly diagnose whether it is pregnancy or pyometra. Veterinary B-ultrasound exploration mainly involves transverse and lateral incision of the uterus. It is easier to operate and interpret the sonogram by transverse inspection with the sound beam perpendicular to the uterine wall. When dogs have pyometra, the enlargement of the uterine cavity is sometimes partial or all, so the size of the cross-section of veterinary B-ultrasound is different in different positions of the same dog or in the same position of different dogs. Since some dogs have no obvious clinical symptoms after mating, and their abdominal circumference gradually increases, the owner mistakenly thinks that they may be pregnant. At this time, it is necessary to distinguish them from veterinary B-ultrasound images of pregnancy. The sonogram of pregnancy should show a liquid dark area with amniotic fluid, and irregular fetal echo structure can be scanned, and some parts are even strong echoes. However, when pyometra occurs, veterinary B-ultrasound images cannot show echo structures similar to the fetus, so it is possible to distinguish whether it is pyometra or pregnancy.