Photon-counting computed tomography, a newer imaging technology that registers individual X-ray photons and separates their energy levels, allows radiologists to quantify how much iodine-based contrast agent accumulates within a tumor. A new exploratory study has now tested whether those quantitative iodine readings correspond to clinical, serologic, and histopathologic characteristics of pancreatic ductal adenocarcinoma, one of the most lethal human cancers. The findings, published in BMC Medical Imaging, suggest that selected iodine measurements show a nominal inverse association with the tumor marker CA 19-9, but the authors caution that the results are hypothesis-generating and require validation in larger independent cohorts.
The retrospective single-center study included 27 patients with histologically confirmed pancreatic ductal adenocarcinoma who had undergone pretreatment contrast-enhanced photon-counting CT. Iodine concentration was measured independently by two blinded readers in both the arterial and portal-venous phases of the scan. The researchers used two region-of-interest approaches: a whole-tumor region drawn on the largest axial section of the tumor, and a second region restricted to the solid component of the lesion. From these measurements, they derived absolute iodine concentrations, tumor-to-aorta normalized iodine ratios, and phase-to-phase differences in iodine values.
CA 19-9, the most widely used serum biomarker in pancreatic cancer, was available for 24 of the 27 patients, with a median value of 123.5 units per milliliter and an interquartile range spanning 55.3 to 1962. The team analyzed the relationship between this marker and the iodine parameters continuously using Spearman rank correlation, treating any cutoff-based and clinicopathologic subgroup comparisons as secondary exploratory analyses that were re-examined with two-sided Wilcoxon rank-sum tests. All reported p-values were nominal, reflecting the exploratory design.
The central finding was a consistent inverse relationship between CA 19-9 and specific iodine measurements. Higher CA 19-9 levels were associated with lower portal-venous absolute iodine concentration in the solid tumor component, with a Spearman correlation coefficient of -0.45 and a 95 percent confidence interval of -0.77 to -0.04, reaching a nominal p-value of 0.028. The association was even stronger for the arterial whole-tumor normalized iodine ratio, where the coefficient was -0.58 with a 95 percent confidence interval of -0.84 to -0.14 and a nominal p-value of 0.010.
When the investigators applied a commonly used clinical threshold of 100 units per milliliter for CA 19-9, they found that portal-venous solid-component absolute iodine concentration was higher in patients below the cutoff than in those above it, measuring 1.77 plus or minus 0.57 milligrams per milliliter versus 1.19 plus or minus 0.50 milligrams per milliliter, with a nominal p-value of 0.017. This cutoff-based comparison aligned with the continuous correlation results, reinforcing the pattern that tumors in patients with lower tumor marker levels showed greater iodine accumulation in their solid portions during the portal-venous phase.
Not every hypothesized relationship survived scrutiny. After the conservative two-sided re-analysis, previously reported differences in iodine parameters by T category, Ki-67 proliferation index, and tumor-cell count did not reach nominal significance. The authors interpret this as evidence that associations with tumor stage and histopathologic parameters were not consistent in this small cohort, underscoring the preliminary nature of the work and the risk of overinterpreting subgroup findings in exploratory imaging studies.
One result stands out for its robustness: interreader reliability was excellent across all iodine parameters, with intraclass correlation coefficients ranging from 0.960 to 0.989. This near-perfect agreement between two independent blinded readers suggests that photon-counting CT iodine quantification is a highly reproducible measurement technique, an essential prerequisite for any imaging biomarker that might eventually be used in clinical decision-making or multicenter trials.
The technical basis for these measurements lies in the energy-discriminating detectors of photon-counting CT, which enable quantitative assessment of tissue iodine distribution rather than relying solely on subjective visual assessment of contrast enhancement. By normalizing tumor iodine values to the aorta and by comparing arterial and portal-venous phases, the study captured multiple complementary dimensions of tumor perfusion and iodine uptake, each of which was tested against the clinical and pathological variables available for the cohort.
The authors conclude that in this small exploratory cohort, selected absolute and normalized iodine measurements showed nominal inverse associations with CA 19-9, whereas associations with tumor stage and histopathologic parameters were not consistent after conservative two-sided re-analysis. They emphasize that these findings are hypothesis-generating and require validation in larger independent cohorts before any incremental clinical value can be inferred. For now, the study establishes that iodine quantification on photon-counting CT is technically feasible and reproducible in pancreatic ductal adenocarcinoma, while leaving open the question of whether these measurements will ultimately add diagnostic or prognostic value beyond existing tools.
Subject of Research: Photon-counting CT iodine measurements and their association with clinical and histopathological parameters in pancreatic ductal adenocarcinoma
Article Title: Photon-counting computed tomography in pancreatic ductal adenocarcinoma: correlation of iodine concentration with histopathological and clinical parameters
Article References: Saeed, S., Helbing, J., Niehoff, J., Haag, N. P., Katz, M., Muecke, R., Saehn, M.-J., Elhabash, S., Lang, S. A., Moenninghoff, C., Kroeger, J. R., Borggrefe, J., Surov, A., & Woeltjen, M. M. (2026). Photon-counting computed tomography in pancreatic ductal adenocarcinoma: correlation of iodine concentration with histopathological and clinical parameters. BMC Medical Imaging, 26(1), Article 583. https://doi.org/10.1186/s12880-026-02980-2
Image Credits: AI Generated
DOI: 10.1186/s12880-026-02980-2
Keywords: photon-counting CT, pancreatic ductal adenocarcinoma, iodine concentration, CA 19-9, quantitative imaging, tumor imaging biomarker, interreader reliability, retrospective study, radiology, oncology imaging, Photon-counting, computed
