RSNA 2016

Abstract Archives of the RSNA, 2016


VSIO21-06

Spectral Photon-counting CT: Spatial Differentiation of Static Contrast versus Radiopaque Image-able Drug Eluting Microspheres

Monday, Nov. 28 2:50PM - 3:00PM Room: S406B



Amir Pourmorteza, PhD, Bethesda, MD (Presenter) Researcher, Siemens AG
Ayele Negussie, PhD, Bethesda, MD (Abstract Co-Author) Nothing to Disclose
Rolf Symons, MD, Washington, DC (Abstract Co-Author) Nothing to Disclose
William F. Pritchard JR, MD, PhD, Bethesda, MD (Abstract Co-Author) Nothing to Disclose
Elliot B. Levy, MD, Bethesda, MD (Abstract Co-Author) Nothing to Disclose
Bradford J. Wood, MD, Bethesda, MD (Abstract Co-Author) Researcher, Koninklijke Philips NV; Researcher, Celsion Corporation; Researcher, BTG International Ltd; Researcher, W. L. Gore & Associates, Inc ; Researcher, Cook Group Incorporated; Patent agreement, VitalDyne, Inc; Intellectual property, Koninklijke Philips NV; Intellectual property, BTG International Ltd; ; ; ;
David A. Bluemke, MD, PhD, Bethesda, MD (Abstract Co-Author) Research support, Siemens AG
PURPOSE

Spectral CT makes it possible to differentiate two or more high atomic number contrast agents (CA) or drug delivery vectors that otherwise cannot be separately resolved using single energy CT or fluoroscopy. Here we demonstrate the feasibility of using a single spectral photon-counting CT (PCCT) scan to image and localize both custom and FDA-cleared microspheres mixed in one of two FDA-cleared CA’s to assess the spatial heterogeneity of microspheres vs CA, which would be desirable after transarterial embolization (TAE).

METHOD AND MATERIALS

Two combinations of microspheres and vascular CAs were studied: I+Gd (LC Bead LUMI iodinated microspheres and gadolinium-based CA (Magnevist, Bayer)) and Bi+I (custom fabricated bismuth-engineered microspheres and iodinated CA (Isovue 300, Bracco)). Vascular phantoms were fabricated with beads inside 4-mm plastic tubes (resembling small vessels) with vascular CA diluted to approximate clinical concentrations. A prototype whole-body PCCT scanner (Siemens Healthcare) was used. Using test tubes with calibrated dilutions of CAs, we searched for energy thresholds that maximized the separation between the CA inside the bead and the vascular CA, while minimizing image noise.  The lower threshold was set at 22 keV and the higher threshold was swept around the k-edge energies of Gd and Bi (50, 90 keV). Images were reconstructed with color maps correlating to these different PCCT detections.

RESULTS

The high energy threshold was incremented by 3keV steps at 80 and 140 kVp tube voltage settings. The following threshold and tube voltage settings provided optimized material separation and image noise tradeoff (I+Gd: 52 keV at 80 kVp and Bi+I: 75 keV at 140 kVp). Linear material decomposition of the PCCT images showed clear differentiation between beads and vascular CA.

CONCLUSION

The results show the feasibility of tuning the spectra thresholds of a PCCT scanner in order to differentiate radiopaque microspheres from adjacent static columns of contrast following embolization. Such differentiation may optimally inform endpoints in embolization or locations of tumor at risk for under-dosing or under-treatment. Future work will include in vivo experiments in a large animal model.

CLINICAL RELEVANCE/APPLICATION

Photon-counting CT may be used to characterize the outcome of TAE by localization and differentiation of microspheres and vascular columns of contrast between microspheres in a single scan.