SU-G-206-12: The Correlation Between Table Height and Patient Size in CT: A Simple Way to Properly Position Patients

• Published in: Medical physics (Lancaster) 2016-06, Vol.43 (6), p.3642-3642
• Main Authors: Szczykutowicz, T, Janssen-Saldivar, E, Miller, D, Malkus, A
• Format: Article
• Language: English
• Subjects: Acoustic noise measurement; Computed tomography; Computer modeling; Data analysis; Germanium; Height measurements; Image analysis; Liver; Medical image noise
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.4956953

Purpose: Proper patient positioning is essential in CT to ensure automatic exposure control functions properly, noise uniformity, and CT number uniformity. This work describes how table height can be used as a surrogate for proper patient positioning and motivates incorporating table height recommendations as a function of patient size into technologist training programs. Methods: Scan data were acquired from 551 adult and pediatric patients under IRB approval. The table height, mean anterior-posterior patient dimension, and mean lateral patient dimension were calculated for each patient. Table height as a function of a patient size surrogate was then analyzed. The mathematical relationship between table height and a properly positioned cylinder was derived and used to fit the data. Patient scans showing proper positioning, and positioning both too high and too low in the gantry were analyzed by measuring the image noise within anterior and posterior regions of the liver. Results: The slope of our fits to patient data matched the mathematical model well, suggesting our technologists are on average properly positioning patients at isocenter. The predicted slope for table height versus anterior-posterior width is 0.5; we measured 0.48±0.006. Patients with table heights more than 2 sigma from the mean table height for their size were shown to have noise non-uniformities greater than 13 HU across the liver which demonstrates how knowing the patient size and table height can predict the image quality of the subsequent CT exam. Conclusion: Our results motivate training technologists to pay attention to the table height. Doing so could easily stop an adult receiving a pediatric positioning and vice versa. Additionally, our results can guide the construction of low end CT scanners lacking vertical table motion by defining the range of table heights used at our clinical practice for a particular patient age and size. Research support provided by GE Healthcare. TPS supplies CT protocols to GE Healthcare under a licensing agreement.