The use of ultrasound in the diagnosis of many female disorders is undisputed. This mode of imaging uses ultrasound waves to reflect off various tissues as they pass through the targeted part of the body from a handheld probe. The reflections are then collected and analyzed to generate a computerized image of the scanned organ.
Transabdominal sonography (TAS) sends a beam of ultrasound waves through the anterior abdominal wall over the region of the distended urinary bladder, which acts as an acoustic window. That is, it allows the ultrasound energy to pass through it freely and so enter the abdomen without deviation.
However, the probe is placed far away from the organs to be imaged, which means that lower frequencies of energy are used. This may reduce the image quality. Another problem occurs in heavily built women because the fat tissue in the anterior abdominal wall deviates the beam hitting the internal organs and consequently reduces the sharpness of the image.
As a result, a novel approach was described in 1985, when the first vaginal ultrasound probe was used. This reduced the distance to the organs imaged, so that higher ultrasound frequencies were used, providing in turn better resolution. The deformation effect caused by the anterior abdominal wall fat is also avoided. The patient also does not have to suffer the discomfort of a full bladder, and the use of color Doppler can be added to the technique.
Thus transvaginal sonography (TVS) rapidly caught on in popularity. The transducer is longer and thinner than the abdominal probe and it is inserted about 2-3 centimeters into the vagina, after covering it with a sterile condom or plastic cover, which is then coated with sterile cool gel to enable a seamless interface between the skin and the transducer.
TVS uses a narrower beam of ultrasound waves, and thus provides a more restricted field of view. For this reason, a cursory transabdominal scan is usually performed first to rule out any mass lesion outside the purview of the TVS transducer, or after the TVS with the bladder still empty to minimize patient waiting and discomfort.
The latter is performed because it is felt that a mass outside the TVS field of view is usually large enough to be seen without an acoustic window on a TAS scan. Some patients may not feel comfortable with the procedure, and it is not suitable for children.
If the lesion is within the uterine cavity, a variant of TVS (also known as saline infusion sonohysterography, SIS) which uses saline to first distend the cavity is used. It gives excellent clarity for lesions such as endometrial thickening or polyps without the use of additional contrast or exposure to radiation.
In most cases no special preparations are required prior to the test. Overall, the test takes about 45 minutes to an hour in a majority of cases, and the results are usually available within 24 hours.