Many different cameras are used for ultrasound. They vary in frequency, shape and size. They are called transducers because they convert electrical energy into physical waves called sound waves and vice versa. Sometimes, the transducers are named according to which part of the body for which they are used.
The abdominal transducer is used to scan body organs by placing the transducer on the abdomen or pelvis. It is used for abdominal ultrasound, which examines the pancreas, liver, gallbladder and spleen. It is used for renal ultrasound, which is a kidney scan. It is also used to examine the female pelvic organs: the uterus and ovaries. The abdominal transducer generally transmits ultrasound waves between the frequencies of two and five megahertz.
The transvaginal transducer is used to examine the female pelvic organs. A range of frequencies can be used with the transvaginal transducer, but the frequency generally averages 10 megahertz. The transducer is inserted vaginally for close inspection of the uterus and ovaries. First trimester pregnancies are also evaluated using transvaginal sonography. Transvaginal ultrasound is also called endovaginal ultrasound.
Different body structures require different frequencies in order to obtain the best possible exam. Structures that are large and dense often require a lower frequency, and the abdominal transducer may be optimal. Large cysts, which are fluid-filled sacs, may also be better visualized with the abdominal transducer. Smaller structures, including small cysts, are often better visualized with higher-frequency ultrasound. Higher frequency ultrasound requires less distance for the sound waves to travel, so transvaginal sonography allows the camera to be placed right next to the organs.
Ultrasound cannot be used to see through bowel gas, which may obstruct the view of the abdominal organs. If abdominal ultrasound is performed, fasting for eight hours prior to the exam is necessary to allow the bowel gas to subside. For pelvic ultrasound, the abdominal transducer is used to look through a filled bladder to visualize the uterus and ovaries. The filled bladder pushes bowel out of the way. Since the filled bladder is a large, cystic structure, it must be emptied for transvaginal sonography.
Abdominal transducers are often wiped clean with a towel. If body fluids contact the transducer, a disinfectant is used to clean the transducer. Transvaginal transducers are covered with a condom or specialized transducer cover during an examination. Upon completion of the examination, the transducer cover is discarded, the transducer is wiped clean, and the transducer is placed in a cold sterilization fluid.