The examination can be performed by transabdominal ultrasonography, generally with a full bladder which acts as an acoustic window to achieve better visualization of pelvis organs, or by transvaginal ultrasonography with a specifically designed vaginal transducer. Transvaginal imaging utilizes a higher frequency imaging, which gives better resolution of the ovaries, uterus and endometrium (the fallopian tubes are generally not seen unless distended), but is limited to depth of image penetration, whereas larger lesions reaching into the abdomen are better seen transabdominally. Having a full bladder for the transabdominal portion of the exam is helpful because sound travels through fluid with less attenuation to better visualize the uterus and ovaries which lies posteriorly to the bladder. The procedure is by definition invasive when performed transvaginally. Scans are performed by gynecologists trained in ultrasound.