The Study Of Dual-energy CT Materials Decomposition And MR Relaxation Techniques For Assessing Liver Iron Overload

OBJECTIVES To assess the feasibility of materials decomposition technique based on dual-energy CT for quantification of liver iron content in iron overload animal models and compare its diagnostic performance with MR relaxation.MATERIALS AND METHODS Fifty-one rabbits of iron-loaded model were established by intravenous injection different doses of iron dextran. Dual source dual energy CT was performed at 80 k Vp and 140 k Vp for liver scanning. Virtual iron concentration(VIC) images were derived from an iron-specific, three-material decomposition algorithm. Hepatic attenuation on VIC images were measured and difference of 80 k Vp and 140 k Vp(ΔH) was calculated. MR relaxation parameters including R2 and R2* were obtained from spin echo and gradient echo sequences,respectively. Hepatic R2 and R2* values were calculated on workstation. All rabbits were sacrificed for Prussian blue stain after finishing CT and MR scanning. Postmortem assessments of LIC were conducted on inductivelycoupled plasma(ICP) spectrometer. The correlations between CT measurements(VIC and ΔH) and LIC, as well as MR measurements(R2 and R2*) and LIC were analyzed. Diagnostic performance of dual-energy CT and MR in discriminating different LIC thresholds was evaluated by receiver operating characteristic(ROC) analysis.RESULTS The iron over load rabbit models were established successfully. LIC of our models was from 0.2 to 39.6 mg Fe/g dry tissue measured by ICP. VIC and ΔH were highly correlated with LIC and the correlation coefficient was 0.977 and 0.975, respectively. For discriminating clinically significant LIC thresholds(1.8, 3.2, 7.0, 15.0 mg Fe/g dry tissue), ROC analysis revealed that the corresponding optimal cutoff value of VIC was 19.6, 25.3, 36.9, 61.5 HU, respectively,while the ΔH was 13.1, 16.2, 23.0, 39.3 HU, respectively. Paired ROC analysis of VIC and ΔH for discriminating different LIC thresholds showed no statistics difference in diagnostic performance(P > 0.05). Hepatic R2 and R2* were highly correlated with LIC with correlation coefficient of 0.965 and 0.975, respectively. For discriminating clinically significant LIC thresholds, ROC analysis revealed that the corresponding optimal cutoff value of R2 was 43.48, 53.98, 79.35,111.13 Hz, respectively, while the R2* was 115.21, 161.53, 661.94, 1164.33 Hz, respectively. The area under ROC curves of R2* were all above 0.95 for different LIC thresholds. When the LIC threshold was set above 3.2 mg Fe/g, dual energy CT showed no significant differences with MR for quantification and grading LIC(P > 0.05).CONCLUSIONS Our iron over load rabbit model study indicated that both dual-energy CT material decomposition parameters and MR relaxation could quantify and grade LIC in various severity iron accumulation situation. Dual-energy CT exhibited similar diagnostic performance with MR, especially for accurate diagnosis of clinical significant liver iron accumulation(LIC > 3.2 mg Fe/g).Purpose To assess the diagnosis performance of materials decomposition based on dual-energy CT and MR relaxation technique for quantification and grading liver iron content in patients suspected of liver iron overload.Materials and Methods Fifty-six subjects suspected of having liver iron overload(serum ferritin concentrations > 500 μg/L) were enrolled in our study. All subjects examined with dual-energy CT(80 and 140 k Vp) and MR liver scanning. Thirty-four of 56 subjects undergone Ferri Scan scanning. VIC images were generated from dual-energy analysis with iron specific slope based on three materials decomposition theory. Hepatic CT attenuation difference(ΔH) were calculated. Hepatic relaxation parameter including R2* and R2 were acquired with gradient-echo sequences and Ferri Scan, respectively. Correlations between VIC, ΔH and R2, R2*were analyzed. The liver iron content(LIC) obtained from Ferri Scan was set as a reference standard. Based on LIC scale thresholds used in iron chelation therapy, Receiver operating characteristic(ROC) analysis was used to calculate the cutoff values and corresponding sensitivity and specificity. The diagnostic performance for dual-energy CT and MR in liver iron quantification and stratification were evaluated by paired ROC analysis.Results VIC and ΔH were significantly correlated with R2*(with correlation coefficients of 0.885 and 0.859, respectively, P < 0.0001). VIC and ΔH were significantly correlated with Ferri Scan-LIC(with correlation coefficients of 0.871 and 0.868, respectively, P < 0.0001). To discriminate among different LIC thresholds of 1.8, 3.2, 7.0, and 15.0 mg Fe/g, the corresponding optimal cutoff values for VIC were 2.50, 5.13, 8.93, and 17.97 Hounsfield units(HU), for ΔH were3.15, 3.40, 5.38,and 12.50 HU,for R2* were 55.11, 86.25, 144.52,and 375.13 Hz, respectively. The area under the receiver operating characteristic curves(AUCs) for both VIC and ΔH increased with the increase of LIC thresholds, while the AUC for R2* kept stable for all LIC thresholds. In the compare analysis of VIC and ΔH showed no significant difference in all LIC thresholds. Paired ROC analysis of VIC and R2* indicated significant difference(0.837 vs. 0.995, P < 0.05) at the LIC threshold of 1.8 mg Fe/g. When the LIC thresholds was set above 3.2 mg Fe/g, all AUC values of VIC and R2* were above 0.950 and the AUCs showed no significant difference(P > 0.05).Conclusion VIC, ΔH and R2* values were highly correlated with liver iron content determined by Ferri Scan. Materials decomposition based on dualenergy CT could accurately quantify and stratify liver iron accumulation in patient. Materials decomposition based on dual-energy CT exhibited a similar diagnostic performance to that of MR in diagnosis of clinically significant liver iron accumulation.