Instrumentation of echocardiographic imaging

The long axis plane of the left ventricle is obtained by placing the transducer on the chest wall, overlying the cardiac structures, directing a beam (broad shaded line) through the heart (upper row, left). As each structure is encountered it reflects ultrasound which is then detected by the instrument during its "listening" mode. These detected structures are displayed as a row of spike arranged according to their relative distances from the transducer; this is known as amplitude modulation or A-mode. The width of each spike at its base is proportional to the size of the structure creating it. When the object being imaged is viewed in real time, the spike will be seen to shift position. Since the A-mode display is not convenient for pattern recognition, its signal is modulated to brightness or B-mode. The height of each spike is expressed as dot brightness and its width as dot diameter. The dots, when played across a photosenstive strip chart or oscillographic display can leave a permanant paper or video tracing known as a time-motion mode record or M-mode echocardiogram. Various means of producing real time two dimensional images or sector scans are shown on the bottom row. A single beam of ultrasound is played back and forth through a sector; as the beam sweeps it leaves several thin lines of B-mode information. When viewed in video or digital format, these lines and dots are visually integrated and produce a real time tomographic cross section of information that precisely replicates an anatomic slice along plane.