Quality Assurance, Acceptance Testing, and Artifact Troubleshooting
Core concepts
QA ensures stable image quality. Daily QA checks SNR, uniformity, geometric accuracy, and ghosting using a phantom. Acceptance testing verifies specifications at installation: field homogeneity, gradient linearity, slice thickness, and RF calibration. ACR phantoms are standard for accreditation.
Metrics
- SNR: signal mean / noise standard deviation (correct for multichannel arrays).
- Uniformity: variation across a uniform phantom.
- Geometric accuracy: measured vs known distances.
- Ghosting: signal in background regions.
Troubleshooting logic
Match artifact to cause: zipper → RF leak; herringbone → vibration; spike/point → data error; shading → coil or B₁ issue. Verify with a phantom before blaming the patient.
Traps
Confusing precision (repeatability) with accuracy (trueness). Forgetting that SNR measurements must use the same coil and sequence settings across time.
Rule of thumb
If a phantom scan is clean but patient scans show artifacts, suspect patient-related causes (motion, implants, anatomy). If the phantom also shows the artifact, suspect hardware or calibration.