In a QA study using a tissue-equivalent phantom, adjusting a brightness control changes reflector brightness from fully bright to barely visible. Which system parameter are you evaluating?

In a QA study using a tissue-equivalent phantom, adjusting a brightness control changes reflector brightness from fully bright to barely visible. Which system parameter are you evaluating?

• A. Resolution
• B. Slice thickness
• C. System sensitivity
• D. Dynamic range

Answer: (C)

The key idea being tested is how well the system detects and displays weak echoes. When you adjust the brightness (gain) and watch a reflector in a tissue-equivalent phantom go from clearly bright to barely visible, you’re examining the scanner’s sensitivity—the ability to pick up and present low-amplitude echoes. If the reflector remains visible as you lower the brightness, the system is highly sensitive; if it quickly disappears, sensitivity is limited. This is distinct from resolution (how well close structures are separated), slice thickness (the elevational thickness of the beam), and dynamic range (the span of echo intensities the display can represent).

The key idea being tested is how well the system detects and displays weak echoes. When you adjust the brightness (gain) and watch a reflector in a tissue-equivalent phantom go from clearly bright to barely visible, you’re examining the scanner’s sensitivity—the ability to pick up and present low-amplitude echoes. If the reflector remains visible as you lower the brightness, the system is highly sensitive; if it quickly disappears, sensitivity is limited. This is distinct from resolution (how well close structures are separated), slice thickness (the elevational thickness of the beam), and dynamic range (the span of echo intensities the display can represent).