M-MODE (ULTRASONIC) SCANNER

Typical Number in Hospital: 2

Cost Bands: 5,6

References: 1

Alternatively known as a time motion (TM) scanner, time position (TP) scanner, motion (M-mode) scanner, echocardiograph, or ultrasonic cardiograph (UCG), this is an ultrasonic scanner which traces the movements of reflecting tissue interfaces with time. It is used primarily to study the action of the heart, particularly the valves, but is also used to study the movement of blood vessels and foetal heart.

The apparatus consists of an A-scanner with the hand-held transducer positioned over the heart. The A-scan signal is turned into a single-line B-scan (i.e. the intensity of the echoes is used to modulate the brightness of dots on a single line on the screen ) and this line is swept slowly up or across the screen so that the movement of reflecting surfaces is seen. The image can be transferred to a permanent record via a fibre-optic recorder or Polaroid camera. The image is often presented alongside an ECG recording and/or phonocardiograph (PCG) to identify the timing of the events seen.

It comprises a high-voltage generator to activate the transducer, a receiving amplifier, a circuit to compensate for the absorption of sound with depth (time-gain compensation), a demodulator, and video amplifier to present the echoes as bright spots on the screen. A time-base is also required to generate the scan lines and move the line across the screen. Special circuits are often added to derive a varying voltage corresponding to the movement of a particular surface or heart valve leaflet.

Such devices are usually found in the cardiac department for the investigation of heart valve defects.