Purpose: NYC requires daily CT QC to follow the requirements of the facility’s accreditation body while NYS requires water CT #, noise, and uniformity to be performed using a common technique setting. With the goal to meet regulatory requirements, almost identical daily QC protocols were set up on all CT scanners at our institution. Initial limits were established by the QMP based on available data and ACR recommendations. This study retrospectively evaluates the feasibility of the approach and appropriateness of these limits.
Methods: Manufacturers’ CT phantoms were scanned axially and helically on 13 CT scanners (GE, Philips, Siemens, Toshiba). Center CT #, noise, and uniformity were recorded for both scan modes. According to the ACR, center CT # of water should be 0 ± 3HU and must be 0 ± 5HU; uniformity should be 0 ± 5HU and must be 0 ± 7HU, whereas limits for noise should be locally established by the QMP. Based on review of past daily CT QC, our institution established a universal limit of 0 ± 5HU for center CT # and uniformity and 7HU for noise.
Results: Center CT #, noise, and uniformity were analyzed for a median of 245 (183 – 360) days for each unit and mode. For all scanners and modes, the average values were -0.11 ± 1.02HU, 1.02 ± 0.72HU, and 4.56 ± 0.78HU for center CT #, uniformity, and noise, respectively. Excluding the axial uniformity of the Philips unit, the difference between average and limit exceeded at least three standard deviations regardless of manufacturer, model, or scan mode.
Conclusion: Universal daily CT QC is feasible on multiple makes and models. As part of quality improvement, decreasing the limits to 0 ± 3HU for both center CT # and uniformity (excluding the Philips unit), and 6.5 for noise, is possible.