How Images Are Obtained

An ultrasound transducer (shown on right) is placed onto the patients skin with the gray area in full contact with the skin. Gel is used between the skin and transducer to prevent air from intervening between the two. The transducer emits a narrow beam of sound waves of a specific high frequency. Depending on the frequency, the sound penetrates the patient's tissues to a variable depth and are refracted, scattered, absorbed or reflected. The reflected waves (called an echo) bounce from tissues back to the transducer, which also acts as a sensor, or detector, and are used to generate the image.

High frequency sound waves provide high resolution images, but don't penetrate deeply into tissues, so are best for superficial structures. Lower frequency sound waves are used to image deeper structures, but create lower resolution images.