Modes of Ultrasound Scanning

Medical Ultrasound which is also known as Diagnostic Sonography or Ultrasonography is a diagnostic imaging technique using ultrasound. It produces images by considering the time taken to be received after the transmission and the strength of the Ultrasound waves received back.

Medical imaging uses several modes of ultrasound.

• A-Mode
• B-Mode (2D mode)
• M-Mode
• Doppler Imaging
• PI-mode
• Harmonic mode
• C-Mode

A-Mode

It’s otherwise known as amplitude mode, which is mainly used for ophthalmology, to detect problems in the optic nerve. This mode displays amplitude spikes of different heights and consists of X and Y axis. The x-axis represents the depth and Y-axis represents the amplitude.

B-Mode

B-Mode is also known as brightness mode, it displays image as large and small dots. Large dots represent the strong echoes and small dots represent the week echoes. The brightness of dots depends upon the amplitude or intensity of the echoes.

There is no Y axis in B-Mode, instead of that there is Z axis which represents the amplitude or intensity.

M-Mode

This mode is also called motion mode. It is commonly used for calculating fractional shortening and ejection fraction. This mode displays movements of structures continuously. Higher sampling rate provides high time resolution so that even rapid motion can be recorded, measured and displayed.

Doppler Imaging

This mode provides visualization of blood flow in the heart or vessel.

• Colour Doppler: Velocity information is presented as a colour-coded overlay on top of a B-mode image
• Continuous wave (CW) Doppler: Doppler information is sampled along a line through the body, and all velocities detected at each time point are presented (on a timeline)
• Pulsed wave (PW) Doppler: Doppler information is sampled from only a small sample volume (defined in 2D image), and presented on a timeline.

PI mode

In this mode, two successive pulses with opposite signs are emitted and then subtracted from each other. This implies that any linearly responding constituent will disappear while gases with non-linear compressibility stand out. Pulse Inversion may also be used in a similar manner as in Harmonic mode.

Harmonic Mode

In this mode, a deep penetrating fundamental frequency is emitted into the body and a harmonic overtone is detected. This way noise and artefacts due to reverberation and aberration are greatly reduced. Some also believe that penetration depth can be gained with improved lateral resolution; however, it is not well documented.

C-Mode

A C-mode image is formed in a plane normal to a B-mode image. A gate that selects data from a specific depth from an A-mode line is used; then the transducer is moved in the 2D plane to sample the entire region at this fixed depth. When the transducer traverses the area in a spiral, an area of 100 cm² can be scanned in around 10 seconds.