EchoMasters: Sonography Songs and Lectures

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The spatial pulse length is determined by the number of cycles within the pulse and its wavelength.
1. Number of Cycles within the Pulse:
- Applying a damping block behind the piezoelectric material prevents it from resonating for a long time, similar to placing a wet rag on a cymbal.
  Increasing dampening reduces the number of cycles released in the pulse, which shortens the SPL and, consequently, improves axial resolution.
- A shorter pulse length directly correlates with better axial resolution, creating a lower quality factor pulse with a greater range of frequencies.
2. Wavelength and Frequency:
- Reducing the wavelength of the ultrasound pulse will shorten the SPL and improve axial resolution.
- The wavelength is inversely proportional to the thickness of the piezoelectric material; a thinner material produces shorter wavelengths and higher frequencies.
  
  Therefore, higher frequency ultrasound waves result in better axial resolution.
- However, high-frequency probes experience quicker attenuation, which can limit the depth of the image despite providing better resolution.

Importantly, axial resolution does not change with depth as the ultrasound pulse travels through tissues.
While the intensity of the pulse decreases with depth, its frequency and spatial pulse length remain constant.
Axial resolution is solely determined by the spatial pulse length, which is influenced by the beam's quality factor (dampening and number of cycles) and the wavelength or frequency of the ultrasound beam.