Questions and Answers
Where should the object be for the best ultrasound image?
At the focal zone
What kind of reflection occurs when there is a small difference in acoustic impedance ($ ext{ΔZ}$) between two tissues?
Low reflection
What material is commonly used between the transducer and patients' skin to aid ultrasound imaging?
Thick liquid (jelly)
What change occurs to a sound wave as it passes from one tissue to another with different sound velocity?
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What should be the orientation of the US transducer to minimize refraction?
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Which statement is true regarding large differences in acoustic impedance ($ ext{ΔZ}$)?
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What is the equation for acoustic impedance ($Z$)?
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What happens to the direction of sound waves as they pass through different tissues?
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Which tissue type typically uses the lowest acoustic impedance in ultrasound imaging?
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Why is jelly used between the ultrasound transducer and the patient's skin?
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Study Notes
US Image Production
- Three key concepts affecting US image production: focal zone, acoustic impedance, and refraction
Focal Zone
- Objects should be at or near the focal zone of the probe for optimal imaging conditions
Acoustic Impedance
- Calculated using the formula: Z = pv
- Small ΔZ (difference in impedance) results in low reflection and high transmission of ultrasound waves
- Large ΔZ results in high reflection and low transmission of ultrasound waves
- A thick liquid (jelly) is used between the transducer and patient's skin to reduce ΔZ and allow easy passage of ultrasound waves
- When an ultrasound wave encounters a boundary between two tissues with different impedance values, a fraction of the wave energy is backscattered towards the transducer, with the remainder being transmitted through the boundary
Refraction
- Refraction occurs when the sound wave changes direction as it passes from one tissue to another with a higher or lower sound velocity
- To minimize refraction, the US transducer should be positioned perpendicularly to the interface between the two media
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