The focal zone marker is ideally adjusted to a position just below the target structure under study.
The more sophisticated ultrasound systems provide the possibility to select two or more focal zone markers.
Some simpler ultrasound systems do not allow adjustment of the exact position of the focal zone. Instead it is possible to select among a few steps.
The size of the displayed image can be adjusted using the depth controls.
When the depth of the field-of-view (FOV) is increased, it becomes possible to see deeper structures.
When the depth is decreased, the FOV is narrowed around structures closer to the probe, thereby omitting the deeper structures.
Reduction of the depth means that the time from emitted to received signal is reduced. This allows a higher frame rate. Higher frame rate can be used to increase the spatial or temporal resolution or the sector width.
The goal of depth adjustment is to align the target structure to the center of the monitor and to visualise the entire target structure inside the visual field.
Undergain:
If the user sets the gain control too low, the result is that the amplification of the electrical signals becomes too small and the 2D greyscale image on the screen becomes too dark. That is called “undergain”.
Overgain:
If the user sets the gain control too high, the result is overamplified electrical signals including artefactual noise and the 2D greyscale image becomes too bright (white) with loss of resolution.
The gain user control is similar to the brightness control of a television set.
Some of the emitted echo signal is reflected back to the probe when the emitted beam hits a reflective interface in the tissue.
The echo signal returning to the probe from the tissue is converted to an electronic signal by the probe. The electronic signal is very weak and has to be amplified before it is processed to a grey scale dot to be displayed on the screen.
The signal amplification is called “gain”.
TGC is a user controlled selective amplification of signals reflected from particular depths in the tissue. TGC compensates for the depth dependent attenuation of the ultrasound wave.
A typical user control panel is illustrated in the image.
By fine-tuning TGC, optimal image quality can be achieved at all depths of the image.
Some low-range ultrasound systems do not have built-in TGC.
A lot of modern ultrasound systems have a user control called “Autogain”. When you press it, the ultrasound system optimises the gain based on the selected probe, ultrasound program and image depth.
The depth is adjusted with the depth control buttons. The depth scale is typically visible along the right side of the ultrasound image.
The size of the displayed image can be adjusted using the depth controls.
When the depth of the field-of-view (FOV) is increased, it becomes possible to see deeper structures.
When the depth is decreased, the FOV is narrowed around structures closer to the probe, thereby omitting the deeper structures.
Reduction of the depth means that the time from emitted to received signal is reduced. This allows a higher frame rate. Higher frame rate can be used to increase the spatial or temporal resolution or the sector width.
