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Basic Ultrasound Physics

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  1. Section 1

    What is Ultrasound ?
  2. How Are Images Generated ?
  3. Ultrasound Physics Videos
  4. Section 2
    Artifacts
  5. Section 3
    Probe Characteristics
  6. Knobology
  7. Imaging Modes
  8. Section 4
    Scanning & Display Orientation

Quizzes

Basic Ultrasound Physics Knobology
Lesson 6 of 8
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Knobology

Introduction

Knobology refers to using the machine adjustments and settings to obtain the best image quality. Image optimization is another term. Hand held portable ultrasound probes used in point of care ultrasound are simple devices that often do not have the functionality of cart based ultrasound machines. Depth and Gain settings are almost universal to all devices.

Image Quality

The goal of ultrasound imaging is to obtain a clinically useful and accurate anatomical representation of the organ being scanned.

This depends on a number of factors. Firstly, ensure good contact between the surface of the probe and the patients skin. Using gel avoids the presence of air which would otherwise hinder transmission and receiving of ultrasound waves.

Other important settings include:

  1. Gain
  2. Depth
  3. Sector Width
  4. Resolution
  5. Contrast
  6. Artifact Suppresion

Gain

Ultrasound images with low, high and optimal gain settings
Figure 1. Ultrasound images with low, high and optimal gain settings.

This is a post-processing function that increases the amplitude of returning ultrasound signals. Increasing gain will brighten the image on the display. Set the gain so that fluid (anechoic & non reflector) appears black on the display.

The brightness of tissues will depend on how well they reflect ultrasound. Good reflectors like bone will therefore appear brighter than soft tissue. Too little gain will cause images to be dark and difficult to visualise. Excessive gain will lead to a granular appearance and accentuate the appearance of artifacts.

Depth

Depth setting for ultrasound image optimization.
Figure 2. There is excessive depth on the left.

The next important knobology function is depth. Adjust the depth setting on the display so that all structures of interest appear on the screen. Probe selection is another important consideration. Use a probe with low frequency (curvilinear probe) for scanning deeper structures. A high frequency linear probe is useful for more superficial structures.

References & Further Reading

  1. Performing a basic ultrasound examination: Roadmap for radiology residents. Yu et al. Radiographics 2019.