What is Dynamic Range?

Late pregnancy in a dog

‘Dynamic range’ is a control on professional ultrasound machines and refers to the range in amplitude (strength) between the strongest and weakest echoes detected by the transducer. The dynamic range of an ultrasound transducer needs to be wide (typically 60dB) in order to detect both very strong, specular reflections from tissue interfaces, and very weak, scattered reflections from the texture within tissue. The dynamic range of a monitor – the range of amplitudes it is capable of displaying to the ultrasound technician – however, is much smaller (typically 20dB). For all of the received information to be meaningfully displayed, therefore, the ultrasound machine must compress echoes ranging across 60dB into only 20dB (Hoskin, Martin & Thrush, 2010). It does this by non-linear amplification, i.e., by boosting weak echoes in relation to stronger ones.

The level of compression can be adjusted by the user, and the optimal level required depends on the application. When discerning subtle differences within a largely homogenous tissue, a wide dynamic range is more helpful. A veterinarian may use a wide dynamic range when imaging the liver, for example. Equally, a wide dynamic range can provide more detail in the tissue of a developing foetus in late pregnancy (55 days+ in canines). When imaging an early pregnancy (around 30 days in canines), on the other hand, it may help to apply more compression so that there is more contrast between the black gestation sacs and the surrounding tissue, prioritising detection over detail.

Ultimately, the optimal dynamic range depends on the specific situation and user preference, and on some ultrasound machines users frequently choose not to manually adjust this control at all. The Scan Pad, for example, is set to a dynamic range deemed optimal for the vast majority of small animal pregnancy scanning applications. In a recent poll, we found that Scan Pad users performing pregnancy scans on dogs, cats and goats, adjust this control far less frequently than users of other models. In comparison, the SonoScape A5v tends to display a very ‘milky’ image by default, as the manufacturers have optimised it for general abdominal scanning as opposed to pregnancy scanning in particular. With this machine, it is common for users to adjust the default dynamic range setting to produce more striking images for pregnancy scanning.

 

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Results of our informal poll, 04/02/2018: We asked our customers, the majority of whom focus on canine pregnancy scanning, “how often do you adjust dynamic range on your ultrasound machine?”

17 Scan Pad users responded, 100% of which “never or occasionally” adjust dynamic range on their machines.

14 KX5600v users responded, 29% of which “never or occasionally” adjust dynamic range on their machines. The remaining 71% reported “frequently” adjusting this control.

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