Katharine Grant PhD, Abstract Co-Author: Employee, Siemens AG

Bernhard Schmidt PhD, Presenter: Employee, Siemens AG

Richard L. Morin PhD, Abstract Co-Author: Advisory Board, American Imaging Management, Inc

To determine the feasiblity of quantifying iron within liver tissue using second-generation Dual Source (DS) Dual Energy (DE) CT scanners. Simulations show that iron concentrations as low as 1 mg/mL can be measured with CT. Early results from first generation DSDE systems were not very convincing, however, due to significantly improved spectral separation (addition of Tin filter: Sn) and several image quality improvements in second-generation DSDE systems, we expect a much improved result.

A phantom study was conducted to determine the ratios of the CT values of iron at the different kVs used for DE acquisitions (80 / sn140kV and 100 / sn140kV). These ratios serve as inputs for the 3 material decomposition, which allows for determination of the iron concentration within liver tissue. The ratio we define is found by measuring the average offset of CT values for different concentrations of iron in comparison to water at the different voltages. The ability for quantification depends on radiation dose and the amount of iron. For hemochromatosis, iron concentrations in the liver are reportedly around 4-5 mg/ml. Thus, feasibility of iron quantification was assessed with an iron salt (Fe2(NO3)3•9H20) dissolved at different concentrations in water (1, 1.5, 3, 6, and 9 mg/mL). Post processing was completed using a clinically available DE application modified with regard to the DE ratio for iron, to support iron specific concentration measurements at each of the different voltage combinations.

The ratio of the CT values at the two different kVs (slope in the 3 material decomposition line for iron) was calculated to be 2.1 for 80kV/sn140kV, and 1.75 for100kV/sn140kV. Our results show that to obtain iron concentrations, CT values need to be multiplied by specific factors for each kV combination: 0.96 and 1.45 mg/mL, for 80kV/sn140kV and 100kV/sn140kV, respectively. Comparison of true and measured concentrations shows excellent agreement. Smaller observed errors were found with higher doses/concentrations.

Our results indicate that DSDE CT scanners with tin filters (Sn) provide enough spectral separation to quantify iron and calculate iron concentration in phantoms. Ex vivo studies are needed to validate the method within liver tissue for patients.

DSDE CT scanning may provide a non-invasive method for diagnosing hemacromatosis or help in predicting liver transplant rejection.

Grant, K, Schmidt, B, Morin, R, Phantom Study to Assess the Feasibility of Quantifying Iron in the Liver Using New Generation Dual-Source Dual-Energy CT Scanners.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11011559.html