Author: Jeremy S. Bredfeldt, Cindy I. Hancox, Arianna Liles, Alex Marques, Usha Tedrow 👨🔬
Affiliation: Department of Cardiology, Brigham and Women's Hospital, Harvard Medical School, Department of Radiation Oncology, Brigham and Women's Hospital, Harvard Medical School 🌍
Purpose: Ventricular tachycardia (VT) can be treated using cardiac radioablation. 4DCT simulation is commonly used, however, contrast injection timing is challenging. This study aimed to develop a protocol for optimizing injection timing to achieve optimal ventricular contrast.
Methods: Optimization of 4DCT ventricular contrast was performed using Siemens Confidence scanner with measurements of two variables: time for the scan to reach the heart and time it takes for contrast to pool in the left ventricle. The difference in these two variables gives the time when the contrast injection should start. The required volume and duration of the contrast agent (Omnipaque) were determined by calculating the time it takes to scan from the top to the bottom of the heart, then subtracting the average time it takes for the contrast to reach the bottom of the heart post-injection. The total contrast volume was then calculated based on a thoracic protocol flow rate of 3 mL/s.
Results: If the top of the heart is X cm from the start of the scan, the time to reach the heart (Y) in seconds is 7.1 + 2.9X, where 7.1 and 2.9 are derived from the scan parameters. The delay time (T) in seconds to start the injection after scanning begins is Y – 27, where 27 seconds is required for contrast to reach the heart. The total volume of contrast needed is 133mL. Histograms of HU values of the blood pool versus the septum found that the standard protocol yielded a contrast 8 HU versus the new protocol of 150 HU.
Conclusion: This model was successfully implemented on two patients. The updated protocol yields contrast over nineteen times that of the old protocol. Optimized contrast injection to maximize ventricular visualization has the potential to improve target delineation accuracy for the purposes of cardiac radioablation.