Room: Room 205
Purpose: Diagnostic Reference Level (DRL) is a typical radiation metric reported for achieving optimum dose and patient safety. DRLs represent "only a first step in the overall optimization process" (IAEA). Therefore, the concept of DRL needs to be expanded to incorporate diagnostic quality. The objective of this work was to expand DRL to new dose and noise reference levels that together simultaneously incorporate radiation dose and image noise across clinical patient populations in Computer Tomography.
Methods: This IRB-exempt study included 2793 examinations performed by two scanners from two vendors and two clinical protocols (abdominopelvic with and chest without contrast). A unique informatics system developed in house automatically extracted protocol information, patient diameter, dose, and in vivo noise magnitude within images. Five reference patient size intervals were identified: 21-25, 25-29, 29-33, 33-37, and 37-41 cm. Noise Reference Level (NRL), Noise Reference Range (NRR), Dose Reference Level (DoRL), and Dose Reference Range (DoRR) were defined for each size range as median and interquartile interval of noise and dose, respectively.
Results: In chest studies, NRLs ranged between 11.5 to 12.9 HU with NRRs for the five size ranges were the following: 11.0-11.9, 12.1-13.5, 12.0-13.9, 11.3-13.6, and 11.5-14.0 HU. Chest DoRLs ranged within 4.7-14.6 HU. The five DoRRs were 4.2-5.1, 4.0-6.0, 6.0-8.2, 9.1-12.9, and 12.5-15.5 mGy. In abdominopelvic studies, NRLs ranged within 10.1-12.1 HU with NRRs of 9.4-11.8, 10.5-12.6, 10.3-12.8, 9.6-12.9, and 10.7-13.7 HU. Correspondingly, DoRLs ranged between 5.0-16.7 mGy and the five DoRRs were 4.4-5.6, 5.7-7.8, 7.9-11.1, 9.6-17.3, and 12.6-20.5 mGy.
Conclusion: New reference levels and ranges, which simultaneously consider image noise and radiation dose information across patient populations, were defined and calculated for two clinical protocols. The new metrics could provide unique and useful information toward the goal of managing image quality and dose in clinical imaging.