Measurement of prostate size and volume is of practical importance in urological practice. The authors compared two commonly used transabdominal and transrectal ultrasound methods of prostate measurement and verified the accuracy of the measurement with a model test, which is reported below. 1, Data and methods General data There were 240 patients, aged 21-89 years, average 64 years, all diagnosed with prostate disease. The instrumentation used was the American-made HDI-3000 color ultrasound diagnostic instrument. A convex array frequency probe with 3-4 MHz was used for the abdomen, and an axial high-frequency fan-shaped intracavitary scanning probe with 5-9 MHz was used for the rectum. Patients were placed in the supine position with a properly filled bladder, and routine abdominal ultrasound examination was performed. Longitudinal and transverse views of the prostate are obtained via the body surface on the pubic rim of the lower abdomen. The images were observed and the anterior-posterior diameter (i.e., thick diameter), right and left diameters (i.e., transverse and wide diameters), and superior and inferior diameters (i.e., long diameters) of the prostate were measured. The patient is then placed in a left lateral position with the hips and knees flexed to expose the buttocks. The intracavitary probe is coated with an appropriate amount of coupling agent, sheathed with a condom and lubricated externally, and slowly inserted into the rectum. The depth of the probe was adjusted to obtain longitudinal, transverse and oblique sections of the prostate for observation and measurement. The values of each diameter of the prostate measured through the abdominal wall and through the rectum were recorded respectively. The prostate volume was calculated by the formula V=0.52*anterior and posterior diameters*left and right diameters*inferior and superior diameters. To confirm the difference between physical and image measurements, the authors designed a model test in which a fluid-filled air sac model of similar morphology and size to the prostate was taken and its three diameters were measured with calipers, and then ultrasound images were obtained by probing the air sac with an intracavitary probe in a water bath to measure its three diameters, and each diameter was repeated 30 times to obtain the average value for comparison. 2, Results There was a significant difference between the two compared and the volume of the prostate measured via the abdominal wall was larger. There are three methods of ultrasound measurement of the prostate: transabdominal wall, transperineal and transrectal. The transperineal route is less used because of the poor quality of the images obtained and the inconvenience of the operation. The transabdominal method is simple and easy to perform, and there are no special requirements for the instrument. However, because of the pubic bone obstacle, the angle of exploration cannot be perpendicular to the longitudinal axis of the gland, obesity, poor bladder filling and small prostate, the abdominal wall ultrasound cannot clearly display the prostate and produce errors in the measurement diameter. Since the adoption of the transrectal pathway for ultrasound exploration of the prostate, not only does it provide a clear sonogram of the prostate in these situations, but it also allows for comprehensive measurements. Because the probe is close to the gland and the measurements are accurate, it is an ideal means of measuring the prostate. Hastak: et al. have experimentally measured the volume of 15 water bladders of different sizes from 20-155 ml with an interventional ultrasound probe and found a significant correlation between the measurements and the actual volume of the water bladder with a standard error of 3.2 ml. Although the in vivo examination is not identical, it is sufficient to show that transrectal measurements of the prostate are somewhat correct. The accuracy of the transrectal method of measurement was also demonstrated by the authors when they repeated an actual test with a specimen similar to Hastak:. In this study, the anterior-posterior, superior-inferior, and superior-inferior diameters and volumes of the prostate measured by transabdominal wall were greater than those measured by transrectal measurements, indicating that the anterior-posterior and superior-inferior diameters of the prostate measured by transabdominal ultrasound have some error and should not be used for volume projection. In the case of prostate enlargement, the increase in the anterior and posterior diameters and the upper and lower diameters of the prostate is often obvious. Therefore, if transabdominal wall ultrasound is applied to measure the size of the enlarged prostate, it will give inconsistent results with the actual and should not be used in clinical practice. The results of the right and left diameters of the prostate were similar between the two testing methods, indicating that transabdominal wall measurements of the right and left diameters of the prostate are reliable, and this result is consistent with the literature. The data from this study showed that the prostate volume obtained by transabdominal wall ultrasound was approximately 20% higher than that obtained by transrectal ultrasound. Therefore, if transabdominal wall ultrasound is used to measure prostate volume, it is appropriate to multiply the value obtained by a factor of 0.8 to estimate the actual prostate volume more accurately. The results of this study indicate that transrectal ultrasound measurement of the prostate is more accurate than transabdominal wall ultrasound measurement. Transabdominal wall ultrasound measurements of the anterior and posterior diameters of the prostate, the upper and lower diameters, and the calculated volumes were larger than the actual values.