Line Density: Reducing Detail to Increase Frame Rate

©Walter Rasmussen, R.D.C.S.

While sweeping through the area being investigated, an ultrasound beam repeatedly emits a pulse which results in individual vertical lines of information. Each “line” has a distinct amount of imaging information and takes time to process.  If some of the lines of are omitted (no pulse is sent out), the machine can dedicate more resources for some other task such as Color Doppler or increasing the Frame Rate, but at the expense of image resolution.

Line Density is available as either a manual or automatic adjustment that is available on various ultrasound scanners.   As line density is decreased, it appears to, “clean-up” the image however, the sonographer should make such adjustments with the knowledge that there will be progressive deterioration of image resolution.

Line density can be temporarily decreased either in order to increase temporal resolution or to make walls and larger structures which may require measurements, easier to perceive, but should not be left at a low setting throughout the exam. An experienced and conscientious sonographer will notice when this adjustment is unnecessarily low and will increase line density whenever possible in order to improve resolution.

In practice, the sonographer can switch between a higher resolution image for small structures and tissue characteristics or a lower resolution image for larger surfaces (such as a heart wall), where high resolution is not critical.

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