A-mode (Amplitude-mode) ultrasound is a technique used to assess organ dimensions and determine the depth of an organ. While A-mode technology was previously employed in midline echoencephalography for rapid screening of intracranial mass lesions and ophthalmologic scanning, it is now considered obsolete in medical imaging. Nonetheless, the A-mode scan has found applications in early pregnancy assessment (specifically the detection of fetal heartbeats), cephalometry, and placental localization.
When the ultrasound beam encounters an anatomic boundary, the received sound impulse is processed to appear as a vertical reflection of a point. On the display, it looks like spikes of different heights (the amplitude). The intensity of the returning impulse determined the height of the vertical reflection and the time it took for the impulse to make the round trip would determine the space between verticals. The distance between these spikes can be measured accurately by dividing the speed of sound in tissue (1540 m/sec) by half the sound travel time.
During an echoencephalography scan, the first A-mode scan is acquired from the right side of the head and captured on film. Subsequently, the probe is positioned at the corresponding point on the left side, and a second exposure is captured on the same film, displaying inverted spikes. The A-mode ultrasound could be used to identify structures normally located in the midline of the brain such as the third ventricle and falx cerebri. The midline structures would be aligned in normal patients but show displacement in patients with mass lesion such as a subdural, epidural, or intracranial hemorrhage.

See also 2D Ultrasound, 3D Ultrasound, 4D Ultrasound, Ultrasound Biomicroscopy, A-scan, B-mode and the Infosheet about ultrasound modes.

Also called B-mode echography, B-mode sonography, 2D-mode, and sonogram.
B-mode ultrasound (Brightness-mode) is the display of a 2D-map of B-mode data, currently the most common form of ultrasound imaging.
The development from A-mode to B-mode is that the ultrasound signal is used to produce various points whose brightness depends on the amplitude instead of the spiking vertical movements in the A-mode. Sweeping a narrow ultrasound beam through the area being examined while transmitting pulses and detecting echoes along closely spaced scan lines produces B-scan images. The vertical position of each bright dot is determined by the time delay from pulse transmission to return of the echo, and the horizontal position by the location of the receiving transducer element.
To generate a rapid series of individual 2D images that show motion, the ultrasound beam is swept repeatedly. The returning sound pulses in B-mode have different shades of darkness depending on their intensities. The varying shades of gray reflect variations in the texture of internal organs. This form of display (solid areas appear white and fluid areas appear black) is also called gray scale.

Different types of displayed B-mode images are:
The probe movement can be performed manual (compound and static B-scanner) or automatic (real-time scanner).
The image reconstruction can be parallel or sector type.

See also B-Scan, 4B-Mode, and Harmonic B-Mode Imaging.

Compound B-mode imaging takes different forms and refers to different methods of creating the ultrasound image.
Real-time compound ultrasound improves the image quality of B-mode scanning by combining ultrasound information obtained from multiple angles. The used averaging process of compound B-mode reduces artifacts and improves the representation of true image data.
B-mode images and Doppler mode images (see also Duplex) can be compounded on the display to improve the visualization of the anatomical relationships between vessels and the surrounding tissues.

The M-mode (Motion-mode) ultrasound is used for analyzing moving body parts (also called time-motion or TM-mode) commonly in cardiac and fetal cardiac imaging. The application of B-mode and a strip chart recorder allows visualization of the structures as a function of depth and time. The M-mode ultrasound transducer beam is stationary while the echoes from a moving reflector are received at varying times.
A single beam in an ultrasound scan is used to produce the one-dimensional M-mode picture, where movement of a structure such as a heart valve can be depicted in a wave-like manner. The high sampling frequency (up to 1000 pulses per second) is useful in assessing rates and motion, particularly in cardiac structures such as the various valves and the chamber walls.

QB-mode (Quadratic Brightness-mode) images are gray scale images from the quadratic component. QB-mode achieves higher contrast and increased dynamic range than the standard B-mode ultrasound images, without loss in spatial resolution.

Gray scale [also grayscale, grey scale = brit.] produces basically black and white images with series of shades of gray. Solid areas appear white and fluid areas appear black, varying from black at the weakest intensity to white at the strongest. Gray scale resolves artifacts as small as 1 mm. The display is made by transmitting bursts of energy and analyzing the returning signal. Gray scale pictures are limited to the gray scale tones; color pictures display more information because the color is added to the gray scale.
Most ultrasound contrast agents also improve gray scale visualization of the flowing blood to such a degree that the tissue echogenicity increases. Gray scale enhancement of flow in an organ promises to improve lesion detection, along with the ability to differentiate between normal and abnormal areas, using many of the criteria already routinely used in CT and MRI.

See also Compress, Densitometry, Triplex Exam and QB-Mode.