Quality control of clinical protocols using the CT accreditation phantom

Abstract

Background: The daily quality control of the computed tomography (CT) system consists of measuring the accuracy of the CT number and artifact evaluation. The annual quality control includes a clinical protocol review. The quality assurance requirements are the responsibility of the CT radiologist, whereas the clinical team reviews and manages the CT protocol to deliver the appropriate radiation dose to the patient for each examination.

Objectives: This study aimed to examine CT number accuracy, review clinical protocols, and verify that the low-contrast performance of clinical protocols was adequate for diagnosis.

Methods: The American College of Radiology (ACR) CT accreditation phantom (CTAP) was scanned by five CT systems with four clinical protocols. The acquisition parameters for the four clinical protocols of each CT manufacturer were set according to the ACR CTAP standard criteria. The CT number calibration was performed, and the low contrast performance in terms of the contrast-to-noise ratio (CNR) was quantitatively evaluated.

Results: The mean CT numbers of polyethylene, acrylic, water, bone, and air were –96, 125, 0, 919, and –993 Hounsfield Unit (HU), respectively. The CNR of the adult brain protocol from the five CT systems was 1.6, 1.8, 1.9, 2.5, and 2.2, and the pediatric brain protocol was 1.5, 1.1, 1.1, 1.1, and 2.0, respectively. The CNR of the adult abdomen protocol was 1.1, 1.1, 1.1, 1.3, and 1.0, and the pediatric abdomen protocol was 0.5, 0.5, 0.5, 1.1, and 0.4, respectively.

Conclusion: The CT numbers in HU were within the calibration criteria for polyethylene (–107 to –84), acrylic (110 to 135), water (–7 to 7), bone (850 to 970), and air (–1005 to –970). The CNR of four clinical protocols were within the ACR Guidelines of the adult head >1.0, pediatric head >0.7, adult abdomen >1.0, and pediatric abdomen >0.4.