Chapter 2
Knobology for the Echocardiogram: Improving Image Quality

Depth

• Adjust depth to fill the entire sector with the heart
• Do not have a lot of useless space below your heart

Figure 2.1 Depth. (a, b) Adjust depth so that the echo image fills the sector. (a) Wasted space below the image; (b) An appropriate depth setting. For details of abbreviations used in the figures, see the Glossary.

Frequency

• Higher-frequency transducers
  • Have shorter wavelengths
  • Have better resolution
  • Have less depth penetration

Figure 2.2 Transducer frequency. (a, b) Higher-frequency transducers provide better image resolution but less depth penetration, while low-frequency transducers can image deeper structures but have poorer resolution. (a) A high-frequency transducer used in a dog. (b) A lower-frequency transducer used in the same dog. Image quality is poorer in panel (b) than in panel (a).

• Lower-frequency transducers
  • Have longer wavelengths
  • Have poorer resolution
    • Not necessarily noticeable in larger animals where structures are larger
    • Noticeably poorer if used in small hearts
  • More depth penetration
• Use the highest frequency that provides adequate depth
• Some machines have resolution, general and penetration settings
  • Resolution is the highest frequency and provides the best quality image but may not go deep enough
  • Penetration is the lowest frequency and will go deeper through the thorax but may not give the best image quality in smaller animals
    • Use penetration for large or difficult-to-image animals
  • The general setting is somewhere in between resolution and penetration

Gain

• This control increases or decreases brightness of the entire image.
• Adjust gain so that structures are easily seen but not so high that pixels start blurring together.
• Some machines have near and far gain knobs.
  • Near gain controls brightness at the top of the sector - the "near field"
  • Far gain controls brightness at the bottom of the sector - the "far field"
  • These near and far gain controls sometimes replace time gain compensation (TGC) sliders on some machines

Figure 2.3 Gain. (a-c) Gain adjusts the overall brightness of the image. Adjust gain to see structures clearly. (a) A low gain setting, where the image is too black and details are difficult to see; (b) A very high gain setting, where the pixels begin to blend together and details are lost. (c) An appropriate gain setting.

Time gain compensation (TGC)

• Sound loses energy as it travels through the thorax
  • This is called attenuation
• Reflections of sound back to the transducer:
  • Are strong in the near field
  • Get weaker with increasing depth
• TGC sliders
  • Each slider controls the gain across the entire sector at a specific depth
  • The goal is to have similar gain settings throughout the entire image from top to bottom
  • Adjust sliders to accomplish this goal
    • Decrease the brightness of strong signals in the near field
      • Move sliders left to decrease gain
    • Enhance the brightness of weaker signals in the far field
      • Move sliders right to increase gain

Figure 2.4 Time Gain Compensation (TGC) curve. (a-c) This adjusts for attenuation (loss of sound energy) as the sound beams travel deeper into the body. Using overall gain would increase gain over the entire image, while TCG sliders control gain at specific depths. (a) Far-field attenuation with low gain. The appropriate TGC sliders should be moved to the right in order to increase brightness at that depth; (b) Too little gain in the near field; the top few TGC sliders should be moved to the right in order to increase the level of brightness in the near field; (c) The TGC curve adjusted so that gain levels are similar from near to far field.

Grey Map

• Reflected sound is assigned brighter or softer shades of grey, based on the map selected
• Some maps show very soft grays, some show very bright levels of grey
• There is no right or wrong here; select the map based on personal preference but that shows the necessary details
• The default map for your preset should be the one that is used the most and is only adjusted if the image is not pleasing
• Adjusting the grey map may provide better image quality in difficult-to-image animals

Figure 2.5 Grey maps. (a, b) Grey maps change the intensity of grays in the image. (a) A gray map with more contrast than in panel (b), which shows softer grays. Adjust based on personal preference without losing image detail.

Dynamic Range

• This controls how many shades of grey are displayed
• This is sometimes called compression
  • The grey levels are compressed into fewer shades if the dynamic range is low
  • The grey levels are expanded into more shades if the dynamic range is high
• Adjust dynamic range for personal preference without losing image details
• The default dynamic range for your preset should be the one that is used the most, and is only adjusted if the image is not pleasing
• Adjusting the dynamic range may provide better image quality in difficult-to-image animals
• Varying combinations of grey map and dynamic range can result in the same levels of grayness and brightness.
  • It does not matter which is adjusted first

Figure 2.6 Dynamic range. (a, b) This knob controls the range of grays displayed. (a) This shows a narrow range of grays; (b) A large range of grays. Select the dynamic range based on personal preference and without loss of image quality.

Rejection

• This button selects the minimum level of sound reflection to be displayed
• Rejection of low-level sound reflections cleans up the background noise
  • Rejection is often used in M-mode images

Figure 2.7 Rejection. (a, b) Low-intensity sound can be "rejected" - removed from the image. (a) An M-mode image without a lot of rejection; (b) The same image with a lot of rejection added; this results in blacker chambers. Here, so much rejection has been added that some details are lost. Rejection is used more often in M-mode imaging than in two-dimensional imaging.

Focus

• The focal point improves resolution at the level it is set
• Typically it is positioned in the bottom half to one-third of the sector image but place the focus at any depth as needed to improve image quality at that location
• In cardiac imaging use no more than one focus

Figure 2.8 Focus. (a, b) The focus allows the beam to be narrowed and display better resolution at whatever depth it is placed. Usually, a symbol of some sort along the depth indicators shows where the focus is (triangles). (a) A focus positioned in the near field. (b) The focus is positioned in the bottom half of the image. Overall resolution is better in panel (b), while far-field structures lack good resolution in panel (a). Place the focus in the area of interest or near the bottom one-third of the sector image.

Scan Area

• Also called sector width
• This sets the width of the sector image
• Wider sectors take longer to process and the frame rate decreases
  • Faster heart rates may require smaller sector widths in order to process the image fast enough
  • Small dogs and cats with fast heart rates often require smaller sector widths for good image resolution
  • Sector width is always smaller for echocardiograms than for abdominal scanning

Harmonics

• Harmonic imaging allows the transducer to send sound out at one frequency but receive sound at a higher frequency
• This usually improves image quality and reduces the number of artifacts
• It does not always work however, and depends on the transducer frequency and the patient
  • Turn harmonics on or off and see which setting provides the best quality image

Figure 2.9 Harmonics. (a, b) Having harmonics on usually provides better resolution and fewer artifacts. It does not always work, however, depending on the transducer frequency and the patient. Turn harmonics on or off and see which setting provides the best image quality. (a) Harmonics on; (b) Harmonics off.

Sweep Speed

• This setting is used for M-mode images
• It spreads out the time line
  • Use a sweep speed that allows for easy...