Implementation of Size-Dependent Local Diagnostic Reference Levels for CT Angiography

Area of Science:

• Medical Imaging
• Radiology
• Radiation Dosimetry

Background:

• Diagnostic reference levels (DRLs) are typically set for standard-sized patients.
• Patient radiation dose in CT examinations is significantly influenced by patient size.
• Existing DRLs may not accurately reflect appropriate dose levels for diverse patient populations.

Purpose of the Study:

• To introduce a method for establishing size-dependent local diagnostic reference levels (LDRLs) in CT.
• To evaluate the efficacy of size-dependent LDRLs compared to size-independent LDRLs.
• To assess the impact of size-dependent LDRLs on image quality in CT angiography (CTA).

Main Methods:

• Included 184 aortic CTA examinations from dual-source CT scanners (CT1 and CT2).
• Retrieved volume CT dose index (CTDIvol) and patient water-equivalent diameter.
• Established size-dependent DRLs via linear regression and size-independent DRLs using percentiles.
• Assessed objective image quality (SNR) and subjective image quality.

Main Results:

• CTDIvol demonstrated dependence on patient size and scanner type (R²=0.72-0.78).
• Size-independent DRLs misclassified a significant percentage of outliers when patient size was considered (30-67%).
• Size-dependent DRLs identified outliers missed by size-independent DRLs (30-70%).
• Negative correlation observed between SNR and CTDIvol, yet all outliers met sufficient subjective image quality standards.

Conclusions:

• A novel method for setting size-dependent LDRLs in CTA has been developed.
• Size-dependent LDRLs provide a more accurate assessment of radiation dose appropriateness for individual patients.
• This approach enhances radiation safety and dose optimization in CT imaging.