Date(s) - 06/05/2014
Clinical Applications of Dual-Source Dual-Energy CT Scanning:
Quantification of Iron Concentration in the Liver as an Alternative to Needle Biopsy for Confirmation of Hepatic Hemochromatosis
Purpose: This study aims to establish an in-vivo baseline of concentration and distribution of normal iron content in the liver (i.e. iron content in a disease-free liver) and perhaps to provide an alternative to needle biopsies to confirm, or rule out, hepatic hemochromatosis via the use of a dual-source dual-energy (DSDE) post-processing software application.
Materials and Methods: Ten water/iron phantoms were scanned using a DSDE 128-slice CT system (SOMATOM Definition Flash, Siemens Medical Solutions, Forchheim, Germany). For the visualization and quantification of iron concentration in the phantoms, three-material decomposition was performed with commercially available post-processing software (Dual Energy, Siemens, Forchheim, Germany) via modification of settings. A conversion factor (mg/mL per HU) between Hounsfield Units and iron concentration was obtained by dividing the known test-tube iron concentrations by the corresponding HU values.
At Mayo Clinic (Jacksonville, FL), patients imaged for kidney stones are scanned with the DSDE CT system. Since the dual energy data sets were acquired, the exams were also processed for iron concentration. Each liver image-study was examined by placing several regions of interest (ROIs) at 5 different slices. The HU values obtained from the ROIs were then converted to mg/mL of iron.
Results: Concentrations ranging from 0.0 to 4.6 mg/mL of iron were observed across 33 patients. The most important observation found was that iron concentration is not uniform within the liver; one case showed significant variation in concentration values, ranging from 0.2 to 4.4 mg/mL of iron within the same image-slice.
Conclusion: Currently, the standard diagnostic test for hemochromatosis is the physiochemical measurement of the liver-iron-content by a needle biopsy. Since the needle can only access a single, very small, region of the liver, the obtained concentration is assumed to be the entire liver concentration. However, as supported by the findings of this study, iron distribution is not uniform within the liver; therefore, a more accurate and less invasive method would be preferable.
Clinical Relevance: This technique can provide a mapping of the distribution of iron in the liver. The method analyzed in this study may provide a noninvasive alternative to needle biopsies to confirm, or rule out, hepatic hemochromatosis.
Future Work: The next step is to look for patients that present symptoms of hepatic hemochromatosis and that are scheduled for a liver biopsy and ask for their consent to the study. The patients will undergo a DSDE CT liver scan prior to the biopsy and the resulting image set will be processed for iron concentration. Once the biopsy results are obtained, iron concentration values will be compared between these results and those obtained with the DE application (with an agreement goal of ±10%).