Quality Control of Clinical Protocols of CT using the Accreditation Phantom

Background: The daily quality control of the Computed Tomography system consists of the measurement of the accuracy of CT Number and the artifact evaluation. The annual quality control includes the clinical protocol review. The CT radiologist is responsible for ensuring that all Quality Assurance (QA) requirements are met. The clinical team reviews and manages the CT protocol to deliver the appropriate radiation dose to the patient for each examination. Objectives: To verify CT Number Accuracy, to review clinical protocols and to verify that the low-contrast performance of clinical protocols is adequate for diagnosis. Methods: American College of Radiology (ACR) CT Accreditation Phantom (AP) was scanned by five CT systems with four clinical protocols. The parameters for 4 clinical protocols of each CT manufacturer were set according to the standard criteria for ACR CTAP. The CT number calibration is performed and the low contrast performance in terms of the contrast-to-noise-ratio (CNR) were evaluated quantitatively. Results: Mean CT number of polyethylene, acrylic, water, bone and air were -96, 125, 0, 919, -993 HU respectively. The CNR of adult brain protocol from 5 CT systems were 1.56, 1.83, 1.94, 2.46, and 2.21 and pediatric brain protocol were 1.48, 1.08, 1.07, 1.10, and 1.97 respectively. The CNR of adult abdomen protocol were 1.05, 1.1, 1.08, 1.30, and1.04, and pediatric abdomen protocol were 0.48, 0.50, 0.52, 1.08, and 0.40 respectively. Conclusion: The CT number were within the calibration criteria of polyethylene -107 and -84, acrylic +110 and +135, water -7 and 7, bone 850 and 970, air -1005 and -970 respectively. The CNR of four clinical protocols were within the ACR Guidelines of Adult head >1.0, Pediatric head >0.7, Adult Abdomen >1.0, Pediatric Abdomen >0.4.