Author: Magdalena Bazalova-Carter, Ross I. Berbeco, James Day, Xinchen Deng, Chelsea Amanda Saffron Dunning, Dianne M. Ferguson, Matthew W. Jacobson, Toby Morris, Marios Myronakis, Jericho Daniel O'Connell, Fides Schwartz, Jainil Shah, Aaron Sodickson 👨🔬
Affiliation: Brigham and Womens Hospital, University of Massachsetts Lowell and Dana-Farber Cancer Institute Boston, Medical Physics Department, Medical School, University of Thessaly, Brigham and Women's Hospital, Harvard Medial School, Dana-Farber Cancer Institute, Department of Radiation Oncology, University of Washington, University of Victoria, Siemens Healthineers, Dana Farber/Brigham and Women's Cancer Center, Brigham and Women's Hospital 🌍
Purpose: While CT imaging has advanced with improved machine design, we propose further gains can be achieved by enhancing sensitivity to contrast agents. Current CT sensitivity is limited to 1% bismuth by volume, while high-Z targeted pharmaceuticals are often present at concentrations of 0.1% or lower. We present a method to increase CT sensitivity for detecting high-Z contrast agents by a significant factor.
Methods: We developed a novel enhanced k-edge CT (EKCT) technique to optimize the k-edge signal of high-Z elements, such as bismuth subsalicylate (BSS) and AGuIX (bismuth nanoparticle therapeutic), using the dual-source Naeotom-Alpha photon counting CT (PCCT). EKCT employs two distinct energy spectra and extensive filtration to isolate relevant photon fluence, improving the contrast-to-noise ratio (CNR) between high and low energy images. The technique was optimized analytically with the Spekpy spectrum generator and a detector response model. We assessed contrast resolution for AGuIX on the Alpha and evaluated EKCT and conventional k-edge CT (KCT) with BSS on a benchtop PCCT. The smallest detectable bismuth concentration in the rectum was determined using the Fastcat hybrid Monte Carlo code. CNR was compared between the Alpha, KCT, and EKCT for 0.15% bismuth.
Results: The EKCT technique included a 110 kVp low energy spectrum (0.89 mm Bi, 3 mm Cu) binned for 76-96.5 keV and a 105 kVp high energy spectrum (6 mm Cu filtration) binned for 90.5-110 keV. On the benchtop PCCT, EKCT showed a 62% increase in k-edge contrast compared to KCT. In MC simulations, the minimum detectable concentration was 0.15%. The CNR in the patient rectum was 6.43 for EKCT compared to 1.28 for KCT and 1.93 for the Alpha.
Conclusion: The EKCT technique significantly improves CT sensitivity, enabling detection of 0.15% bismuth with a CNR of 6.43, representing a major advancement in visualizing low-concentration targeted pharmaceuticals.