During a diagnostic sonogram, which interface will produce the weakest reflected signal?

During a diagnostic sonogram, which interface will produce the weakest reflected signal?

• A. Organ parenchyma/fluid
• B. Organ parenchyma/air
• C. Organ parenchyma/organ parenchyma
• D. Organ parenchyma/bone

Answer: (C)

Ultrasound echoes depend on the difference in acoustic impedance between two media. The bigger the mismatch, the stronger the reflected signal; the smaller the mismatch, the weaker the reflection. Between two tissues of the same type (organ parenchyma touching organ parenchyma), the impedances are very similar, so there’s essentially no boundary to create a strong echo. In contrast, interfaces with fluid, air, or bone involve larger impedance differences and produce stronger reflections. An organ parenchyma–air boundary yields a very strong reflection, and bone creates a strong, bright echo due to the large mismatch. Therefore, the weakest reflected signal comes from an interface between organ parenchyma and organ parenchyma.

Ultrasound echoes depend on the difference in acoustic impedance between two media. The bigger the mismatch, the stronger the reflected signal; the smaller the mismatch, the weaker the reflection.

Between two tissues of the same type (organ parenchyma touching organ parenchyma), the impedances are very similar, so there’s essentially no boundary to create a strong echo. In contrast, interfaces with fluid, air, or bone involve larger impedance differences and produce stronger reflections. An organ parenchyma–air boundary yields a very strong reflection, and bone creates a strong, bright echo due to the large mismatch.

Therefore, the weakest reflected signal comes from an interface between organ parenchyma and organ parenchyma.