Ultrasound Physics & Machine Setting

Ultrasound imaging relies on the physics of sound waves to create images of internal structures. The ultrasound machine's settings, such as gain, depth, and frequency, are adjusted to optimize image quality and penetration. 

Here's a breakdown of key aspects:

1. Ultrasound Basics:

• Sound Waves:

  Ultrasound is high-frequency sound waves, typically 2-20 MHz, that are used in medical imaging. 
• Transducer:

  A transducer converts electrical energy into sound waves and back again, allowing the machine to both send and receive signals. 
• PIEZOELECTRIC EFFECT:

  The piezoelectric effect allows the transducer to generate sound waves when an electrical impulse is applied, and to detect returning echoes. 
• Wave Propagation:

  Ultrasound waves travel through the body, and their speed is dependent on the tissue's stiffness. 
• Attenuation:

  As ultrasound waves travel, they lose energy due to absorption, reflection, refraction, and scattering. 

2. Machine Settings and their Effects:

• Gain:

  This setting controls the brightness of the image. Higher gain amplifies weak signals, making the image brighter, but can also introduce noise. 
• Depth:

  This setting determines how deep into the body the ultrasound waves will penetrate. A deeper penetration requires lower frequencies, which may reduce resolution. 
• Frequency:

  Higher frequencies provide better resolution but have less depth penetration. Lower frequencies have greater depth but less resolution. 
• Focus:

  This setting focuses the ultrasound beam to a point for improved lateral resolution, which is the clarity of the image at the focused depth. 
• Imaging Modes (A, B, M):

  • A-mode: One-dimensional image showing the amplitude of echoes over time. 
  • B-mode: Two-dimensional image (2D) or even 3D. 
  • M-mode: Tracks the movement of structures over time, often used for echocardiography. 

3. Ultrasound Artifacts:

• Acoustic Shadowing:

  Strongly attenuating structures, like bone, can create a shadow on the ultrasound image. 
• Refraction:

  The bending of ultrasound waves at the interface between tissues with different speeds of sound. 
• Reverberation:

  Repeated reflections of ultrasound waves, creating artifacts. 
• Enhancement:

  Increased brightness behind structures with low attenuation, like fluid-filled organs. 

4. Other Considerations:

• Doppler Ultrasound: Used to visualize blood flow and measure velocity. 
• Contrast Ultrasound: Uses microbubbles to enhance the echogenicity of blood flow. 
• Probe Selection: Different types of probes are used for different applications and depths.