Uterine fibroids are diagnosed by pelvic exam and even more commonly by ultrasound. Often, a pelvic mass cannot be determined to be a fibroid on pelvic exam alone, and ultrasound is very helpful in differentiating it from other conditions such as ovarian tumors. MRI and CT scans can also play a role in diagnosing fibroids, but ultrasound is the simplest, cheapest, and best technique for imaging the pelvis. Occasionally, when trying to determine if a fibroid is present in the uterine cavity (endometrial cavity), a hysterosonogram (HSG) is done. In this procedure, an ultrasound exam is done while contrast fluid is injected into the uterus through the cervix. The fluid within the endometrial cavity can help outline any masses that are inside, such as submucosal fibroids.