Beyond CT accreditation: Systematic evaluation of achievable image quality, radiation dose, and protocol factors in...

The purpose of this study was to assess the parameters and performance of CT protocols collected in numerous annual medical physics CT equipment performance evaluations (EPEs), develop clinically relevant performance targets for select phantom tests, and provide guidance for medical physicists about appropriate CT imaging parameters.

The results of CT scanner annual physics testing depend on the clinical protocols used at the facility, with a key image quality parameter dependent on the associated radiation dose. The American College of Radiology (ACR) accreditation process and quality control manual impose criteria on these parameters, but these minimum criteria are not meaningful performance targets for clinically acceptable protocols.

A mathematical relationship between dose and contrast-to-noise ratio (CNR) was developed to evaluate test results and guide protocol adjustments. Historical testing results, including CNR and measured CTDI_vol were collected from 111 completed annual EPEs, and the results were compared to ACR criteria and published guidance on scanning parameters.

The average and 75th percentile CDTI_vol values were markedly lower than the ACR reference values, while the average and 25th percentile CNR values were markedly higher than the ACR minimum reference values. Scanners where iterative reconstruction (IR) was used did not show lower CTDI_vol values than scanners using filtered backprojection. Protocol parameters in routine clinical use showed high rates of deviation from published reference protocols and clinical imaging guidelines.

Modern CT scanners likely can exceed ACR accreditation targets for image quality at radiation dose levels well below the ACR limits. Clinical medical physicists can use the approach described in this study to recommend clinical protocol improvements when performing physics testing. Medical physicists can engage with radiologists and technologists to determine whether published protocol guidelines are appropriate for clinical needs and can use the simple mathematical relationship described in this paper to translate protocols for modifications such as reduced slice thickness.