Sonography Techniques

Humans can hear sounds that range from 20 Hz to 20,000 Hz. As we get older, this range narrows, especially with higher frequencies. Sonography uses high frequency sound waves to examine objects. This harmless technology found its application in diagnosing many diseases. A transducer machine emits ultrasound waves toward an object or an organ in the body. After hitting an object or organ, the waves come back as echoes at different speeds and angles. The information provided by echoes is encoded into an image of the organ that doctors use to make a diagnosis.

A-Mode

• Amplitude modulation (A-mode) is a basic technique of sonography. The received energy is displayed as energy amplitude. In this mode, a single beam of ultrasound is analyzed. The greater the reflection at the interface, the larger the signal amplitude that will be displayed. A-mode is rarely in use today but it is helpful in differentiating a cystic lesion from a solid lesion. It can also be used to measure ocular dimensions.

B-mode

• An amplitude modulation can be converted into simple dots. If the strength of returned amplitude is higher, the dot will be brighter and vice versa. Multiple brightness mode (B-mode) images can be combined to create a 2D brightness scan. Compared with one-dimensional A mode, B mode is a more advantageous technique, except for biometry. B mode requires a highly skilled operator and full cooperation of the patient because of lengthy examinations.

M mode

• Motion (M mode) uses a series of B mode dots to create motion graphics. This enables doctors to measure the motion range of specific organs, such as the heart. M mode formed the basis of echocardiography before real-time sonography systems. Motion technique is often used to evaluate the diaphragmatic motion among children with suspected diaphragmatic paralysis.

Doppler Sonography

• Another noninvasive diagnostic technique is Doppler sonography. The Doppler method examines blood flow velocity. University of Cincinnati research psychologists have used this to measure the level of attention. As reported in "Science Daily" in December 2006, the researchers followed blood flow in the brain to see how long it took for attention to drop. According to the study, people tend to lose concentration after 40 minutes and sometimes after only 10 minutes. Joel Warm, Professor of Psychology at the University of Cincinnati, who conducted the research, says this phenomenon is such "that the more you look, the less you see." Professor Warm believes this technique could be used as an early warning system for pilots, air traffic controllers or other critical task professions. He calls it a way to "monitor the monitor."

New Techniques

• In recent years, 3D and 4D systems have become popular, as these modern position-sensing techniques allow accurate display of acoustic echoes. The systems can be used independently or as add-ons to basic sonography systems. The 3D technique is widely used to display the surface of a fetus in order to detect pathologies such as abdominal wall defects and neural tube defects. The 4D imaging system displays real-time motion of 3D images with the help of specialized transducers. This system is applied in obstetric examination.