Intracellular Ca²⁺ imaging is a mainstay of vascular physiology and is central to studying vascular ion channel function. Ca²⁺ acts as the convergence point for signalling through a wide range of ion channels and receptors (IP₃ receptors, TRP channels, store-operated entry, ryanodine receptors), and the resulting spatial and temporal patterns of Ca²⁺ activity report directly on how these pathways are engaged. Subcellular Ca²⁺ events, whole-cell oscillations, and coordinated activity across a vessel each carry distinct mechanistic information about channel function in health and in disease.

For most researchers, the core requirement is simple: to delineate the cells or regions of interest and quantify how their Ca²⁺ signals evolve over time. Yet the available tools are frequently prohibitive. Some are commercial, with licensing costs beyond the reach of many laboratories; others are free but inflexible, or powerful yet built around a single imaging modality that does not generalise to vascular preparations. Lacking a common platform, each laboratory develops its own approach, undermining the cross-study comparability and reproducibility that funders and publishers increasingly demand.

To address this, we developed Ca²⁺Tracker: a free, open-source application for the interactive analysis of Ca²⁺ imaging data, designed to be fully usable without programming experience. A functional prototype is already operational, with continued development underway (www.calciumimaging.com). It reads the image formats produced by common confocal and widefield systems (TIFF stacks, Bio-Formats) and runs on both Windows and macOS. Regions of interest can be defined manually, semi-automatically across large fields, or generated directly from patterns of spontaneous Ca²⁺ activity, allowing active cells to be identified without prior anatomical segmentation. From these regions, Ca²⁺Tracker extracts ΔF/F₀ traces using flexible baseline-selection strategies that accommodate drifting backgrounds, photobleaching, and variation in resting fluorescence. Ca²⁺ traces can be inspected interactively, and Ca²⁺Tracker quantifies event amplitude, frequency, and rise/fall kinetics directly, with results exported in standard formats for any further analysis.

Critically, Ca²⁺Tracker is designed to support automated comparative analysis across multiple datasets, a capability absent from existing tools and increasingly essential as experiments grow in scale. By standardising core workflows, it offers a common analytical framework where the field currently has none. Ca²⁺Tracker is deliberately general, handling the full range of vascular Ca²⁺ preparations: isolated cells, intact en face preparations, and whole pressurised vessels. Because it is open-source and modular, users can extend it with their own analytical methods and share these with the community as plugins, allowing the tool to grow as the needs of the field evolve.

Ca²⁺Tracker builds on our experience developing VasoTracker, an open-source pressure myography platform now used by vascular laboratories internationally, with its successor (VasoTracker2 ¹) recently published in The Journal of Physiology. Ca²⁺Tracker applies the same iterative, user-centred, openly developed approach. By removing cost and expertise barriers to a core technique and providing a standardised framework for analysis, Ca²⁺Tracker aims to improve reproducibility and broaden participation in vascular ion channel research.