Author: Stephen Bhagroo, Sorour Hosseini, YuHuei Jessica Huang, Jeremy Kunz, Thomas Boyd Martin, Geoffrey S. Nelson, Nicholas Pierre Nelson, Ryan G. Price, Hui Zhao 👨🔬
Affiliation: University of Utah, Department of Radiation Oncology, Huntsman Cancer Institute, University of Utah 🌍
Purpose: To investigate the correlation between HyperSight CBCT imaging dose and image quality.
Methods: Six-series of 174 CBCT scans were acquired using HyperSight on Halcyon (125kV, 133-971mAs, FOV: 282mm, 360mm, and 538mm). Three-series were acquired with the CatPhan 604, and another three-series with CatPhan 604 surrounded by a custom-made polyester annulus to mimic a patient width of 32cm. Image quality was analyzed, including signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), noise, low-contrast visibility (LCV), uniformity index (UI), and integral non-uniformity (INU). The correlation between mAs (imaging dose) and image quality was evaluated.
Results: The SNR and CNR for all material inserts increased with increasing mAs for all scans, with a higher amplitude of increase for scans without the annulus. The SNR and CNR were higher for scans without annulus. For example, for polystyrene (the lowest SNR insert) with 360mm FOV, SNR without annulus ranged from 5.2 to 11.3 and with annulus from 1.4 to 4.1. CNR without annulus ranged from 11.3 to 26.1 and with annulus from 2.9 to 9.5. SNR without annulus was over 5 (Rose criterion) for all materials when exposure was ≥152mAs. SNR with annulus was over 5 for all materials except polystyrene when exposure was ≥366mAs, and SNR was over 3 for polystyrene at ≥568mAs. Both noise and LCV decreased with increasing mAs and were higher for scans with annulus. The UI remains similar with increasing mAs and was slightly higher for scans without annulus. The INU slightly increased with the increase of mAs and was higher for scans without annulus. All parameters were FOV dependent, and generally, the larger the FOV, the better the image quality (except LCV).
Conclusion: For a 20cm diameter object, CBCT acquired at 152mAs would meet Rose criterion. At 32cm, CBCT acquired at 568mAs would achieve SNR of 3 for soft tissue.