Dynamic Range (DR) is the range of echoes which are available to be displayed on the screen at any one time. DR is measured in decibels (dB), the same unit used to measure the intensity of sound).
- Once you have located the DR control, manipulate it and see how it impacts your image. The numerical indicator of the DR you are using is visible on the ultrasound image display as dB.
- Dynamic range determines the number of grey shades displayed and subsequently controls overall contrast i.e., how many shades of grey are displayed between ‘bright white’ and ‘dark black’.
- A high dynamic range setting gives a higher number (wider scale) of greys from white to black which makes for an image with decreased contrast, often referred to as a ‘softer’ image.
- High dynamic range is typically needed for tissue parenchymal assessments, such as liver and spleen, where very similar acoustic properties exist within a structure.
- Increasing the dynamic range (having more levels of grey) will enhance subtle differences between similar tissue types (i.e., tissues with similar acoustic impedance – a low acoustic impedance mismatch) on the screen e.g. liver metastases.
- Reducing the dynamic range decreases the number of grey shades between black and white and so increases the contrast of the image.
- Low dynamic range is especially useful where there are different acoustic impedances between adjacent structures e.g., vascular studies (blood and vessel wall) and other fluid filled areas, needle tip identification (bright needle in soft tissue), musculoskeletal studies, GIT wall layers (mucosa, submucosa, fluid) etc.