Figure 1b. Uterine changes during the menstrual cycle in a 31-year-old woman. (a) Sagittal T2-weighted image obtained during the periovulatory phase shows the anatomy of the three zones: endometrium, junctional zone (arrowheads), and outer myometrium. (b) Sagittal T2-weighted image obtained during the midsecretory phase shows increased thickness of the endometrium and myometrium. The signal intensity of the outer myometrium is increased. The thickness of the junctional zone (arrowheads) is significantly decreased. (c) Sagittal T2-weighted image obtained during the menstrual phase shows that the uterine corpus appears smaller than during the periovulatory and midsecretory phases. The zonal anatomy of the myometrium is ill defined and irregularly thick (
). The low-signal-intensity band in the middle of the endometrium (arrowheads) represents menstrual blood.