An Open, Reproducible Gamma-Variate Pipeline for CT-Perfusion Time–Attenuation Curve Analysis, with Standardized (ASIST-Japan) Map Visualization

CT perfusion (CTP) is central to acute-stroke and oncologic imaging, yet quantitative outputs vary substantially across vendor software, undermining reproducibility. We present an open, transparent core (ctp-core) that fits first-pass time–attenuation curves with a gamma-variate model, derives perfusion indices (peak enhancement, time-to-peak [TTP], bolus-arrival time [BAT], area under the curve [AUC]) analytically from the fitted parameters, and renders parametric maps with the ASIST-Japan standardized lookup table (a-LUT) so that visualization is comparable across sites. Every parameter, bound, and processing step is exposed. The method is validated on Monte-Carlo synthetic curves with known ground truth; no confidential or patient data are used. Across signal-to-noise ratio (SNR) levels 5–100 (200 independent runs per level) the pipeline recovers peak time to within 0.03–0.52 s and peak amplitude to within 0.4–8.1% (mean absolute error), degrading monotonically with noise; at a representative SNR of 20 it recovers peak time within 0.13 s, peak amplitude within 2.0%, and BAT within 0.51 s, with fit quality R-squared = 0.98. The reproducibility demonstration is deterministic (fixed seed) and re-runs to bit-stable metrics. All code, the synthetic-data generator, the standardized-visualization module, evaluation scripts, and a 34-test suite are released openly for independent verification. The contribution is a fully open, parameter-transparent gamma-variate plus standardized-visualization pipeline with reproducible synthetic benchmarks — a reference others can audit, reuse, and build on.