Author: Zhihua Qi 👨🔬
Affiliation: Henry Ford Health 🌍
Purpose: State of the art cardiac CT has built-in automated, patient specific optimization, taking into account a number of factors including patient size, heart rate and others. It is crucial to develop clear understanding of the optimization rationale and perform validation in order to make the best use of the technology in a variety of diagnostic applications. This study presents a practical approach to validating the optimization rationale using clinical data.
Methods: Incorporating information from literature and experimental data, mathematical formulas were developed to estimate the needed tube current and its resulting radiation output as a function of baseline technique, tube voltage, tube current modulation strength, noise constraint parameter, patient diameter and heart rate. The estimated tube current values are compared to the actual tube current values on clinical data. The CT scanner from which clinical data were collected is Somatom Force (Siemens Healthineers), and the selected type of study was coronary CTA.
Results: Observed trends from the estimated techniques as a function of different factors include: (1) radiation output increases with patient size; (2) the relationship between heart rate and radiation output varies with the specific scanning model and technical details; (3) radiation output often plateaus when scanning extra-large patients, highlighting challenges in imaging obese patients. The estimated tube current and CTDIvol values were within 15% of the actual values on more than 75% of the collected clinical scans.
Conclusion: The presented approach can be applied to the validation of vendor’s patient-specific optimization rationale used in cardiac CT. It greatly facilitates the understanding of the often-automated technique optimization of cardiac CT, and provides valuable guidance to the quality assurance activities on these studies performed on patients presented with a wide spectrum of conditions.