Intra-individual consistency of spectral detector CT-enabled iodine quantification of the vascular and renal blood pool.

Objectives: The objective of this study was to evaluate the intra-individual, longitudinal consistency of iodine measurements regarding the vascular and renal blood pool in patients that underwent repetitive spectral detector computed tomography (SDCT) examinations to evaluate their utility for oncologic imaging.
Methods: Seventy-nine patients with two (n = 53) or three (n = 26) clinically indicated biphasic SDCT scans of the abdomen were retrospectively included. ROI-based measurements of Hounsfield unit (HU) attenuation in conventional images and iodine concentration were performed by an experienced radiologist in the following regions (two ROIs each): abdominal aorta, vena cava inferior, portal vein, and renal cortices. Modified variation coefficients (MVCs) were computed to assess intra-individual longitudinal between the different time points.
Results: Variation of HU attenuation and iodine concentration measurements was significantly lower in the venous than in the arterial phase images (attenuation/iodine concentration: arterial - 4.2/- 3.9, venous 0.4/1.0; p ≤ 0.05). Regarding attenuation in conventional images of the arterial phase, the median MVC was - 1.8 (- 20.5-21.3) % within the aorta and - 6.5 (- 44.0-25.0) % within the renal cortex while in the portal venous phase, it was 0.62 (- 11.1-11.7) % and - 1.6 (- 16.2-10.6) %, respectively. Regarding iodine concentration, MVC for arterial phase was - 2.5 (- 22.9-28.4) % within the aorta and - 5.8 (- 55.9-29.6) % within the renal cortex. The referring MVCs of the portal venous phase were - 0.7 (- 17.9-16.9) % and - 2.6 (- 17.6-12.5) %.
Conclusions: Intra-individual iodine quantification of the vascular and cortical renal blood pool at different time points works most accurately in venous phase images whereas measurements conducted in arterial phase images underlay greater variability.
Key Points: • There is an intra-individual, physiological variation in iodine map measurements from dual-energy computed tomography. • This variation is smaller in venous phase examinations compared with arterial phase and therefore venous phase images should be preferred to minimize this intra-individual variation. • Care has to be taken, when considering iodine measurements for clinical decision-making, particularly in the context of oncologic initial or follow-up imaging.