Quantification of iron in soft tissues through fast kV-switching dual-energy CT imaging: What calibration data are required?

Purpose

To provide recommendation on the type of calibration data needed for quantification of iron content in soft tissues through fast kV-switching dual-energy CT (DECT).

Methods

Tissue-specific liquid surrogates mimicking human liver, spleen, kidney and muscles with iron concentration of 0–7 mg/ml were prepared and attached circumferentially to a 16-cm polymethylmethacrylate CT phantom. Soft tissue-equivalent gel boluses were employed to create different in size and configuration phantom-vials setups. Each phantom-vials setup was subjected to fast kV-switching DECT imaging with different acquisition protocols. The virtual iron concentration (VIC) in mg/ml was determined for each vial through the iron(water) material density images. VIC-to-true iron concentration (TIC) curves were derived for four phantom-vials setups and three different acquisition protocols. The applicability of derived VIC-to-TIC calibration data was tested in ten DECT examinations from our institution’s archive.

Results

A linear relationship between TIC and VIC values was observed for all tissue-surrogates and phantom-vials setups (R² > 0.94). The VIC-to-TIC regression-lines derived for different tissues were found to differ significantly (p < 0.05). The regression-lines derived for the same tissue type, but different in size phantom-vials setups were also found to differ significantly (p < 0.05). The effects of DECT acquisition protocol and different vials positioning within the phantom-vials setup on derived regression-lines were found to be minor (p > 0.05).

Conclusions

Quantification of iron content through DECT imaging requires tissue- and patient size- specific calibration data. The presented DECT imaging-based method might be useful for monitoring iron levels in patients suspected of iron mis-regulation.