MEASURING SPHERE‐LIKE STRUCTURES USING TRANSRECTAL ULTRASONOGRAPHY

Sphere–like structures are commonly measured for clinical or research purposes. We measured two diameters, the circumference (perimeter) and cross sectional area of 113 equine ovarian follicles in a water bath then determined the relationships between those measurements and the actual volume of fluid in the follicles. Cross–sectional area, diameter 3 and area 2/3 were all highly correlated with the volume of the structures and superior (p<0.05) to diameter or perimeter as predictors of volume. As predictors of volume, there was no significant difference (p>0.05) between cross‐sectional area, diameter 3 , and area 2/3 . Because of the ease of measuring diameter, we suggest that diameter 3 be used to estimate the actual size of sphere‐like structures by ultrasonographic measurement. A table was generated for clinical use to show how much the largest diameter of a fluid‐filled structure (follicle, cyst, hematoma, etc.) would have to increase or decrease to indicate a significant change in the volume of the structure.