Majority of CT examinations are performed with tube current modulation (TCM), and many of them are also acquired with multiple series. A recent survey of 1352 chest/abdominal/pelvis examinations in an ambulatory CT examination room found that the percentage of multiple series and non-overlapping multiple series was 32.5% and 29.1%, respectively, excluding single rotation axial scan. In CT perfusion and CT-guided interventional procedures, almost all procedures are performed with multiple series. Accurate patient dose evaluation needs to consider each of patient size, tube current profile and dose accumulation from all series.
CT dose index (including CTDIvol) and size-specific dose estimate (SSDE) are used in CT dose monitoring. As originally developed to characterize the phantom dose or patient dose in the central region of a single scan with constant mA, CTDIvol and SSDE are not intended for the examinations with TCM or multiple acquisition series. Recent research and development in CT dosimetry, dose spread function, and the approach to equilibrium function allow tracking the patient dose from the CT examinations under a wide range of CT acquisition conditions, including TCM and multiple acquisition series.
This lecture will provide an overview of CT dose theory of shift-variant CT acquisition modes, implication/practice in CT protocol management and patient dose monitoring, as well as development in tracking patient dose from contemporary CT exams with TCM or multiple series.
1. Understand the physics of TCM dosimetry and the interpretation of its CTDIvol.
2. Understand four major types of TCM schemes and their impact on dose and image quality.
3. Be familiar with data driven CT dose monitoring and protocol optimization.
4. Be familiar with z-axis dose profile evaluation suited for a wide range of CT acquisition conditions.
Funding Support, Disclosures, and Conflict of Interest: None for R.L.D., B.L., D.Z., and X.L. J.M.B is supported in part by NIH grants (R01-CA181081, R01-EB025829, and R01-CA214515).
Not Applicable / None Entered.