Ultrasound Image Computation

After the beam formed RF data passes through all its processing stages, it becomes ready as in input to ultrasound image computation processes. Different types of ultrasound images are used in clinical practice, each conveying a particular type of information to the clinician.

A-Mode Images
The A-Mode image is the most basic type of ultrasound image derived from RF data, and forms the basis for other types of ultrasound images. With the analogy to telecommunications in mind, the A-Mode data is the result of amplitude demodulation of the RF data. In simpler terms, it is a signal that captures the variation in the amplitude of the RF data.

The RF data is an alternating sinusoid whose amplitude and phase are changing. The alternations by themselves carry little information about the structure of tissue being image. On the other hand, the amplitude of the sinusoid shows how much reflection and backscattering has happened at a particular depth in tissue. Therefore the amplitude demodulation is carried out to take out the alternations, and leave the amplitude signal in tact.

Techniques for amplitude demodulation in ultrasound imaging are adapted from telecommunications. The two most popular methods are through the Hilbert Transform, and IQ demodulation.