Ultrasound Modes: A, B, & M

A mode is an operational state that a system has been switched to. A normal mode occurs when all parts of a system oscillate with the same frequency. For ultrasound imaging, different modes are used to examine the arterial/venous system, heart, pancreas, urinary system, ovaries, spinal cord, joints, and more. The different types of modes can be controlled by the operator or tech.

A-Mode, or Amplitude Modulation, is the display of amplitude spikes of different heights. It is used for opthamalolgy studes to detect finding in the optic nerve. A-Mode consists of a x and y axis, where x represents the depth and y represents the Amplitude. The above image shows an example of A-Mode display.

B-Mode, or Brightness Modulation, is the display of 2D map of B-Mode data, and is the most common form of ultrasound imaging. Unlike A-Mode, B-Mode is based on brightness with the absence of vertical spikes. Therefore, the brightness depends upon the amplitude or intensity of the echo. There is no y axis on B-Mode, instead, there is a z axis, which represents the echo intensity or amplitude, and a x axis, which represents depth. B-Mode will display an image of large and small dots, which represent strong and weak echoes, respectively. Below is an example of B-Mode imaging of an echogenic mass in a particular organ.

M-Mode, or Motion Mode (also called Time Motion or TM-Mode), is the display of a one-dimensional image that is used for analyzing moving body parts commonly in cardiac and fetal cardiac imaging. This can be accomplished by recording the amplitude and rate of motion in real time by repeatedly measuring the distance of the object from the single transducer at a given moment. The single sound beam is transmitted and the reflected echoes are displayed as dots of varying intensities thus creating lines across the screen. Below is an TM-Mode one dimensional imaging in a pt with moderate mitral stenosis (calcific) that shows evidence of multiple echoes of the anterior mitral leaflet.

get more information on US modes via us-tip after the jump.