For a given CT scan, though a fairly broad range of scanning parameters may result in acceptable images, the results are often far from optimal. Especially in demanding situations, it may be important to account for the differences, e.g. multi-energy capabilities, between scanner models. Even more important is the variation in size, age, condition and diagnostic need of each patient, especially children. Studies requiring gating may need special attention. Combined, all of these elements can present challenges in designing and modifying CT scanner protocols. One consideration is radiation dose. The scanner provides pre-scan estimates of CTDIvol and DLP. Proper use of these parameters, along with the adjustments for patient size provided by the size specific dose estimate (SSDE) of AAPM Reports 204 and 220 are useful not only for dose comparisons but for creating and modifying protocols and for inter-scanner translation of protocols. Normalized to dose, the fine tuning of scan parameters such as tube potential, current, pitch, rotation time, kernels and iterative reconstruction can significantly affect the quality of the scan. Though the effect of patient size can be ameliorated substantially by automatic modulation of machine parameters, optimization of the protocol can still benefit from fine tuning. In particular, pediatric patients, even after patient size is considered, can have substantially different scanning requirements than do adults. Understanding these differences can sometimes lead to a superior scan at a possibly lower radiation dose but lower doses may not be warranted where specific clinical questions (e.g., microabscesses or dual phase for mesenteric ischemia) need to be answered. Sometimes for adults but more often with children, patient cooperation may be a significant issue. Medical physicists and a radiologist will present information that will lead to a better understanding in the design and implementation of CT protocols.
I: Introduction (Donovan M. Bakalyar, Ph.D.)
II: Practical Considerations for Size Based Protocol Optimization (Zhihua Qi, PhD)
III: CT Protocol Optimization over the Range of Patient Age & Size and for Different CT Scanner Types: Recommendations & Misconceptions (Frank N. Ranallo, PhD)
IV: Meeting the Imaging Needs of the Pediatric Radiologist: The Effect of Patient Size, Age and Clinical Circumstance On Optimizing the CT Image (Kimberly E. Applegate, MD)
1. To make effective use of dose parameters in optimizing CT protocols
2. How best to adjust scanning parameters for optimization of protocols
3. How best to account for patient age, size and clinical needs in scanning pediatric patients