ARDMS SPI Quality Assurance and Phantoms 2 — Questions and Answers
Question 1: Which phantom structure is used to assess axial resolution in an ultrasound system?
- Anechoic cysts of varying depths
- Closely spaced wire targets aligned along the beam axis (Correct answer)
- Speckle-generating material embedded in the phantom
- Beveled surface reflectors at 45 degrees
Correct answer: Closely spaced wire targets aligned along the beam axis
Wire targets placed at known separations along the beam axis allow measurement of the minimum resolvable distance in the axial direction.
Question 2: What does the uniformity test on a QA phantom primarily evaluate?
- Temporal resolution of the system
- Consistency of gray-scale brightness across the image field (Correct answer)
- Accuracy of Doppler velocity measurements
- Spatial compounding effectiveness
Correct answer: Consistency of gray-scale brightness across the image field
Uniformity testing checks that the image brightness is homogeneous throughout the field, revealing gain, TGC, or transducer element dropouts.
Question 3: A QA test reveals that the on-screen distance measurement reads 5.2 cm for a structure the phantom certifies as 5.0 cm. What does this indicate?
- Excessive focal zone depth
- Caliper or distance accuracy error exceeding acceptable tolerance (Correct answer)
- Normal variation within expected system noise
- Artifact from multipath reflection
Correct answer: Caliper or distance accuracy error exceeding acceptable tolerance
A 4% error in distance measurement suggests a calibration issue with the system's speed-of-sound assumption or caliper circuitry.
Question 4: Which parameter is assessed when using anechoic spherical targets of progressively smaller diameter within a tissue-mimicking phantom?
- Frame rate
- Contrast resolution (Correct answer)
- Mechanical index
- Acoustic output power
Correct answer: Contrast resolution
Detecting anechoic spheres against a uniform background tests contrast resolution, which reflects the system's ability to distinguish subtle echo-amplitude differences.
Question 5: Which material property of a tissue-mimicking phantom most directly simulates the acoustic attenuation of soft tissue?
- Speed of sound set to 1540 m/s
- Attenuation coefficient of approximately 0.5 dB/cm/MHz (Correct answer)
- Density equal to water at 37°C
- Impedance mismatch between gelatin layers
Correct answer: Attenuation coefficient of approximately 0.5 dB/cm/MHz
Soft tissue has an attenuation coefficient of ~0.5 dB/cm/MHz, and QA phantoms are formulated to match this value for realistic signal depth behavior.
Question 6: During weekly QA, a sonographer notices the lateral resolution has worsened compared to baseline. What is the most likely cause?
- Phantom temperature dropped below 20°C
- One or more transducer elements have failed (Correct answer)
- The TGC was adjusted incorrectly
- The speed-of-sound calibration changed
Correct answer: One or more transducer elements have failed
Failed or weak transducer elements degrade the aperture and focusing ability of the array, directly worsening lateral resolution.
Question 7: What is the primary purpose of recording baseline QA images when a new ultrasound system is installed?
- To satisfy Medicare billing requirements
- To establish reference measurements for future performance comparisons (Correct answer)
- To calibrate the DICOM network settings
- To document the phantom's serial number
Correct answer: To establish reference measurements for future performance comparisons
Baseline images provide documented reference values so that subsequent QA tests can detect degradation in system performance over time.
ARDMS SPI Quality Assurance and Phantoms 2
Which phantom structure is used to assess axial resolution in an ultrasound system?