Paul Fitzgerald, Presenter: Employee, General Electric Company

Robert E. Colborn PhD, Abstract Co-Author: Employee, General Electric Company

Peter Edic, Abstract Co-Author: Employee, General Electric Company

Benjamin M. Yeh MD, Abstract Co-Author: Research Grant, General Electric Company Consultant, General Electric Company

Andrew S. Torres PhD, Abstract Co-Author: Employee, General Electric Company

High-Z element contrast agents could improve x-ray imaging efficacy and become a better-tolerated alternative to conventional materials for use in clinical imaging. We sought to obtain reliable empirical data in order to compare the performance of candidate elements and assess their potential imaging benefits versus iodine.

We measured the HU of 7 candidate elements (I, Ba, Gd, Yb, Ta, Au, Bi), NaCl and water in a CT phantom using rigorous methods, with and without additional x-ray filters. Samples were formulated at 10 mg active element/mL in distilled water, and concentrations were confirmed by elemental analysis. Samples were placed in 19 mm diameter vials within a modified 32 cm CTDI phantom. Scans were performed on a GE LightSpeed VCT scanner, at 80, 100, 120, and 140 kV, with 0, 0.2, 0.5, and 1.0 mm added Cu filter. HU was measured in a 10 mm ROI and averaged over 16 slices. Data were corrected for measured concentration and Cl content, and contrast relative to water (net HU) was calculated.

The k edge of the active element is the key determinant of net HU. Elements (I, Ba, Gd) whose k edge is below the mean energy of the spectra exhibit a monotonically decreasing net HU with increasing kV and filtration. Among these, Gd provides the highest net HU; I the lowest. Elements (Yb, Ta) whose k edge is near the mean energy of the spectra exhibit net HU that’s more constant with kV and filtration. Yb provides a slightly higher net HU than Ta, and peaks at 80 or 100 kV, depending on filtration; Ta peaks at 100 kV. Elements (Au, Bi) whose k edge is above the mean energy of the spectra exhibit a lower net HU. Au net HU peaks at 120 kV; Bi has a notch at 100 kV, peaks at 140 kV, and is strongly dependent on filtration.

Of the elements we tested, Gd provides the highest net HU per mg of active element; Au and Bi produce the lowest net HU. Concerns for Gd side effects at the high doses needed to produce good HU, and the high cost of Au make these elements more challenging to develop as clinical CT contrast agents. At 100 kV and higher, Yb and Ta produce ~30-90% higher HU than I under the same conditions and merit further consideration, including tests for patient safety. This work was supported by NIH grant R01EB015476. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

Compared to conventional iodine agents, contrast agents based on high-Z elements may offer improved image quality in diagnostic x-ray and CT imaging and could potentially reduce clinical side effects.

Fitzgerald, P, Colborn, R, Edic, P, Yeh, B, Torres, A, CT Image Contrast of Seven High-Z Elements within a 32 cm Phantom and Using Various Additional X-ray Filters.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14004626.html