Intra-patient variability of iodine quantification across different dual-energy CT platforms: assessment of normalization techniques

Objectives

To investigate intra-patient variability of iodine concentration (IC) between three different dual-energy CT (DECT) platforms and to test different normalization approaches.

Methods

Forty-four patients who underwent portal venous phase abdominal DECT on a dual-source (dsDECT), a rapid kVp switching (rsDECT), and a dual-layer detector platform (dlDECT) during cancer follow-up were retrospectively included. IC in the liver, pancreas, and kidneys and different normalized ICs (NIC_PV:portal vein; NIC_AA:abdominal aorta; NIC_ALL:overall iodine load) were compared between the three DECT scanners for each patient. A longitudinal mixed effects analysis was conducted to elucidate the effect of the scanner type, scan order, inter-scan time, and contrast media amount on normalized iodine concentration.

Results

Variability of IC was highest in the liver (dsDECT vs. dlDECT 28.96 (14.28–46.87) %, dsDECT vs. rsDECT 29.08 (16.59–62.55) %, rsDECT vs. dlDECT 22.85 (7.52–33.49) %), and lowest in the kidneys (dsDECT vs. dlDECT 15.76 (7.03–26.1) %, dsDECT vs. rsDECT 15.67 (8.86–25.56) %, rsDECT vs. dlDECT 10.92 (4.92–22.79) %). NIC_ALL yielded the best reduction of IC variability throughout all tissues and inter-scanner comparisons, yet did not reduce the variability between dsDECT vs. dlDECT and rsDECT, respectively, in the liver. The scanner type remained a significant determinant for NIC_ALL in the pancreas and the liver (F-values, 12.26 and 23.78; both, p < 0.0001).

Conclusions

We found tissue-specific intra-patient variability of IC across different DECT scanner types. Normalization mitigated variability by reducing physiological fluctuations in iodine distribution. After normalization, the scanner type still had a significant effect on iodine variability in the pancreas and liver.

Clinical relevance statement

Differences in iodine quantification between dual-energy CT scanners can partly be mitigated by normalization, yet remain relevant for specific tissues and inter-scanner comparisons, which should be taken into account at clinical routine imaging.

Key Points

• Iodine concentration showed the least variability between scanner types in the kidneys (range 10.92–15.76%) and highest variability in the liver (range 22.85–29.08%).

• Normalizing tissue-specific iodine concentrations against the overall iodine load yielded the greatest reduction of variability between scanner types for 2/3 inter-scanner comparisons in the liver and for all (3/3) inter-scanner comparisons in the kidneys and pancreas, respectively.

• However, even after normalization, the dual-energy CT scanner type was found to be the factor significantly influencing variability of iodine concentration in the liver and pancreas.