# Quantitative PCCT imaging in differentiating adrenal adenomas from metastases: diagnostic performance and its clinical applications

## TL;DR

Photon counting CT can help distinguish adrenal tumors from metastases using iodine density and virtual non-contrast imaging.

## Contribution

The study introduces PCCT-derived iodine density and VNC reconstructions as a novel method for differentiating adrenal adenomas from metastases.

## Key findings

- VNC reconstructions in portal-venous phase showed significant differences in density between adenomas and metastases (21.64 HU vs. 28.26 HU).
- Relative enhancement in portal-venous phase and IVR of pv showed significant potential for differentiating adrenal lesions.
- PCCT provides additional diagnostic capability but has lower specificity compared to specialized MRI and CT protocols.

## Abstract

To evaluate the potential of Photon counting CT (PCCT) -derived iodine densities and Virtual-Non-Contrast (VNC) reconstructions for the differentiation between adrenal adenomas and adrenal metastases.

This retrospective study enrolled 53 PCCT scans of patients with adrenal lesions (29 adenomas, 24 metastases) including early-arterial (ea) and portal-venous (pv) contrast phase. Iodine maps and VNC reconstructions were calculated from the acquired sequences. Using the measured values, several parameters such as relative enhancement (RE), normalized iodine density (NID), and iodine to VNC ratio (IVR) were calculated. In the acquired image series, iodine maps and VNC reconstructions density values were evaluated (adrenal lesion, ipsilateral adrenal tissue, contralateral adrenal tissue, portal vein, descending aorta, inferior vena cava, subcutaneous adipose tissue, in the first lumbar vertebral body, surrounding air, and in the psoas muscle) and compared.

In total, the measured structures showed significant variation in density values due to different contrast phases and reconstructions. VNC reconstructions of portal-venous contrast phase showed significant differences in measured density mean values between adrenal adenomas and adrenal metastases (21.64 HU vs. 28.26 HU, p: 0.027, AUC: 0.68). No significant differences between metastases and adenomas were observed in iodine concentration, RE of ea, NID of ea and pv, as IVR of ea. Significant alterations were observed in RE of pv (p: 0.023, AUC: 0.7) and IVR of pv (pv: 0.029, AUC: 0.69).

The recent study shows that PCCT derived VNC reconstructions of portal venous contrast phase can be used for reliable differentiation of adrenal adenomas and adrenal metastases and underlines the value of PCCT in oncological imaging.

Photon counting CT enables Virtual-Non-Contrast reconstructions and iodine maps, which can be used for better differentiation of adrenal incidentalomas in contrast-enhanced scans of the upper abdomen.

Density values measured in Virtual-Non-Contrast significantly improve the differentiation of adenomas from metastases of the adrenal gland compared to density values measured in contrast-enhanced scans.

Additionally, several parameters, such as relative enhancement, normalized iodine density, and iodine-to-Virtual-Non-Contrast ratio, can be calculated. In particular, relative enhancement shows great potential to discriminate between adenomas and metastases.

Photon counting CT therefore adds additional capability in diagnosing adrenal glands to routine clinical workflows, providing an improved initial orientation. However, the methods still exhibit lower levels of significance and specificity compared to specialized MRI and CT protocols for imaging of the adrenal gland.