Patient-specific organ dose and in-vivo image quality assessment in clinical CT

To develop and characterize individualized dose and quality measures at organ level compared to their generic counterparts across a clinical CT dataset.

The study included 9801 chest-abdomen-pelvis and abdomen-pelvis CT exams (7,763 patients, mean age, 56 ± 17 years; 4113 women) representing 20 unique protocols. For each exam, patient-specific organ dose of all radiosensitive organs was estimated using a validated method by generating personalized computational phantoms and Monte Carlo simulations. Effective dose (E_OD) was calculated by weighted sum of the organ doses. Liver dose, OD_liver, noise in the liver, N_liver, and observer model detectability, d', were assessed within the liver as examples of individualized, organ-based image assessment measurements. The organ-based measurements (OD_liver, E_OD, and N_liver) were compared to their generic counterparts: ssize-specific ddose estimates (SSDE), effective dose based on dose length product (E_DLP), and whole-body noise (N_global), respectively.

Generic dose values were substantially higher than individualized estimates for SSDE vs. OD_liver (median of all exams: 51.2 %, p < 0.001) and E_DLP vs. ED_OD (median: 41.0 %, p < 0.001). N_global was generally lower than N_liver (median: -7.2 %, p < 0.001). The correlation relationships of E_OD and d' were substantially varied (R² range: 0-0.5) for different patient sizes and scan parameters.

Demonstrated across a population of exams, individualized organ-based measurements of dose and quality are feasible. Generic measures cannot fully represent individualized organ-based values. The correlation relationships between individualized dose and image quality values varies for different vendors and protocols, implying imaging optimization is best when done semi-independently for each factor using individualized measurements.