P1120989

After visuaiization of the urinary bladder the ultra-sound probe is advanced cranialły until the uterus ap-pears on the screen. The probe is placed dorsally on the uterus at the level of the bifurcation. From here the ventrally directed probe is rotated laterally along the uterine hom until the ovary is visualized and then back to the opposite side to the second ovary. In this manner the uterine homs are scanned slice by slice. Each slice represents a sagittally oriented cross section through the uterine hom (Fig. 1.4 and 1.5). After the two homs the uterine body is imaged on the screen. Starting at the bifurcation the probe is withdrawn along the midline up to the level of the cervix. In the process one sees a sagit-tal longitudinal section of the uterine body (Fig. 1.5 and 1.6). During the course of an examination the probe should be moved rather slowly so as to ensure that the entire uterine tract as well as the ovaries and their func-tional stmctures can be assessed. It is important to be aware that only a minor rotation of the probe results in a significant shift of the scanning piane in the depth of the field. A 30 degree rotation of the probe results in a 5 cm movement of the scanning piane at a depth of 10 cm. Fast probe movements and motility of the targeted organs can be additive with the result that important features are passed too ąuickly or even missed.

Organs closely associated with the intemal genitalia can be used as reference points to improve one’s topo-graphical orientation. Very echoic arches in the left ab-domen, usually ventral to the left uterine hom, repre-sent the sacculations of the left dorsal colon. The drastic change in impedance between the gut wali and the gas containing feces undemeath it cause the total reflection of the ultrasound waves. The thin wali of the colon thus appears as a wavy stmcture of high echogenicity. The deeper areas are not reached by enough ultrasound waves and therefore remain almost totally dark. The bony pelvic floor also presents as a hyperechoic stmcture (Fig. 1.2). It is recognizable as anechoic linę caudal and ventral to the uterus and the urinary bladder.

In addition to transrectal ultrasonography, trans-cutaneous ultrasonography can be applied in mares. The transcutaneous approach is less established for rou-tine gynecological diagnostics than the transrectal method. One valuable indication is the visualization of the fetus and its uterine environment during the second and third trimesters of pregnancy (Adams-Brende-muehl and Pipers 1987). Since the hair on the abdomi-nal wali prevents the penetration of the ultrasound waves, the mare’s ventral abdominal hair must be thoroughly clipped very well before performing the ultrasound examination. The majority of mares tolerate the transcutaneous examination less well than the transrectal procedurę.