(TVS) The transvaginal sonography (transvaginal echography or endovaginal ultrasound), uses a small vaginal transducer (5-7.5 MHz) that is inserted into the vagina to depict the inner female organs (uterus, ovaries, vessels). As a general rule, ultrasound works better when the probe is close to the area being examined. Compared with a sonogram through the abdominal wall, the transvaginal technique produces a sharper image, not only because of the close proximity to the uterus, but also because the better signal to noise ratio of the used transducer.

Indications:

The advantage of transvaginal sonography is being able to get very close to the structures of the pelvis, and thus get better images and a more reliable diagnosis.

See also Pelvic Ultrasound, Hysterosalpingo Contrast Sonography.

(UCA / USCA) Ultrasonic contrast agents, also called ultrasound contrast agents, are encapsulated bubbles on the order of 1-10 μm in diameter. These gas bubbles are injected into the blood stream in order to increase blood/ tissue contrast during an ultrasonogram. These microbubbles are filled with air or a gas with a lower solubility in blood than air, such as perfluorochemicals. The microbubble shell consists of albumin, phospholipid, or other material and encapsulates the gas core. Due to this construction, ultrasonic contrast agents are highly compressible, and have a high echogenicity.

See also Ultrasound Contrast Agent Safety.

Ultrasonography is another term[aka: sonography] used to describe the practice of using ultrasound technology for diagnostic imaging. It is synonymous with sonography and signifies the process of capturing ultrasound images, regardless of the body part or condition being examined. Ultrasonography is widely utilized in various medical imaging specialties, including obstetrics and gynecology, cardiology, radiology, urology, and many others. It has proven to be particularly valuable in obstetric imaging, allowing healthcare providers to monitor the growth and development of a fetus during pregnancy.
Ultrasonography uses the reflections of high-frequency sound waves to construct an image of a body organ. These ultrasonic waves are generated by a quartz crystal and are reflected at the interface between different tissues. The transmission and reflection of these high-frequency waves are displayed with different types of ultrasound modes.
See also sonogram, sonography, ultrasound imaging.

(US) Ultrasound is very high frequency sound above about 20,000 Hertz. Any frequency above the capabilities of the human ear is referred to as ultrasound.
Diagnostic ultrasound imaging uses much higher frequencies, in the order of megahertz. The frequencies present in usual sonograms can be anywhere between 2 and 13 MHz. The sound beam produce a single focused arc-shaped sound wave from the sum of all the individual pulses emitted by the transducer.

See also Medical Imaging.

(UCA / USCA) Ultrasonography is the most commonly performed diagnostic imaging procedure. The introduction of sonographic contrast media into routine practice modifies the use of ultrasound in a variety of clinical applications. USCAs consist of microbubbles filled with air or gases and can be classified according to their pharmacokinetics. Among the blood pool agents, transpulmonary ultrasound contrast agents offer higher diagnostic potential compared to agents that cannot pass the pulmonary capillary bed after a peripheral intravenous injection. In addition to their vascular phase, some USCAs can exhibit a tissue- or organ-specific phase.
The sonogram image quality is improved either by decreasing the reflectivity of the undesired interfaces or by increasing the backscattered echoes from the desired regions.

Different types of ultrasound contrast agents:
Ultrasound contrast agents act as echo-enhancers, because of the high different acoustic impedance at the interface between gas and blood. The enhanced echo intensity is proportional to the change in acoustical impedance as the sound beam crosses from the blood to the gas in the bubbles.

The ideal qualities of an ultrasound contrast agent:
A typical ultrasound contrast agent consists of a thin flexible or rigid shell composed of albumin, lipid, or polymer confining a gas such as nitrogen, or a perfluorocarbon. The choice of the microbubble shell and gas has an important influence on the properties of the agent.
Current generations of microbubbles have a diameter from 1 μm to 5 μm. The success of these agents is mostly dependent on the small size and on the stability of their shell, which allows passage of the microbubbles through the pulmonary circulation. Microbubbles must be made smaller than the diameter of capillaries or they would embolize and be ineffective and perhaps even dangerous.
The reflectivity of these microbubbles is proportional to the fourth power of a particle diameter but also directly proportional to the concentration of the contrast agent particles themselves.
Ultrasound contrast agents produce unique acoustic signatures that allow to separate their signal from tissue echoes and to depict whether they are moving or stationary. This enables the detection of capillary flow and of targeted microbubbles that are retained in tissues such as normal liver.
The new generation of contrast media is characterized by prolonged persistence in the vascular bed which provides consistent enhancement of the arterial Doppler signal. Contrast agents make it also possible to perform dynamic and perfusion studies. Targeted contrast imaging agents are for example taken up by the phagocytic cell systems and thus have liver/spleen specific effects.

See also Ultrasound Contrast Agent Safety, Adverse Reaction, Tissue-Specific Ultrasound Contrast Agent, and Bubble Specific Imaging.