Evaluation of Iodine-Based Contrast Agents for Ex Vivo Micro-CT Imaging of Porcine Hearts: An Application to Cardiac Conduction System Imaging

Abstract

Purpose: This study compares two iodine-based contrast agents, iodine in ethanol (I2E) and aqueous solution of potassium triiodide (I2KI), in optimizing high-resolution, contrast-enhanced micro computed tomography imaging (micro-CT) of the cardiac conduction system (CCS) in porcine hearts. The study evaluates their relative efficacy in enhancing tissue contrast and anatomical delineation, aiming to improve CCS visualization for advanced cardiac research. Methods: Dissected porcine hearts were stained with I2E or I2KI for contrast enhancement and scanned with micro-computed tomography. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and volumetric shrinkage were evaluated. Additionally, qualitative visualization of CCS-related anatomical landmarks, such as the sinoatrial node (SAN), atrioventricular node (AVN), and Purkinje fibres, was performed, along with assessment of artefact occurrence and sample integrity. The efficacy of the contrast agents was also determined by segmenting the regions of interest corresponding to the CCS from micro-CT images. These were then further validated against histology. Results: I2E provided superior CNR, fewer artefacts, and preserved sample integrity, enabling smooth post-processing and histological sectioning. I2KI staining produced higher soft-tissue signal intensity and faster stain saturation (day 2) than I2E (day 3). However, I2KI exhibited leaching and introduced substantial staining artefacts. I2KI also exhibited structural disintegration, which, in turn, compromised downstream processing. Conclusion: These results suggest that I2E is a viable alternative to I2KI for CCS micro-CT imaging when sample preservation and downstream analyses are essential, whereas I2KI may be preferred for rapid, high-intensity staining where tissue integrity is less critical.