Ultrasonography

Ultrasonography is a diagnostic imaging method for "visualization of deep structures of the body by recording the reflections of echoes of pulses of ultrasonic waves directed into the tissues. Use of ultrasound for imaging or diagnostic purposes employs frequencies ranging from 1.6 to 10 megahertz." In contrast, ultrasonic therapy is "the use of focused, high-frequency sound waves to produce local hyperthermia in certain diseased or injured parts of the body or to destroy the diseased tissue."

The technique physically involves sending acoustic energy from a transducer, far above the human hearing range (1.6 to 20 MHz), into the area of interest, receiving reflections of that energy, and converting the image to clinically useful images. Higher frequency improves resolution, but reduces tissue penetration.

Examinations of different parts of the body, for different reasons, have different names, optimal frequencies, means of display, and places to apply the transducer. For example, an echocardiogram visualizes the heart. When the transducer is applied to the chest, the result is a transthoracic echocardiogram, but if the transducer is placed in the esophagus, the study becomes a transesophageal echocardiogram(TEE).

Display modes

There are four modes of display:

• A-mode.
• B-mode (brightness mode). "brightness varies with the intensity of the reflected waves"
• M-mode (Motion mode).
• B-scan.

Variations

Doppler ultrasonography is "ultrasonography applying the Doppler effect, with frequency-shifted ultrasound reflections produced by moving targets (usually red blood cells) in the bloodstream along the ultrasound axis in direct proportion to the velocity of movement of the targets, to determine both direction and velocity of blood flow."

Ultrasonography can be done after the heart has been stressed by exercise or drugs; the latter view would be called stress echocardiography or "stress echo".