Diffusion-constrained delay-domain selection for rapid enhanced truncated-correlation photothermal coherence tomography imaging of vascular-like structures in the intact mouse head

Non-contact photothermal imaging can probe optically absorbing structures through the intact scalp, but delay-resolved enhanced truncated-correlation photothermal coherence tomography (eTC-PCT) maps are shaped by thermal diffusion, correlation gating, and anatomical interference. A quantitative rule is, therefore, required for selecting excitation and reconstruction parameters without relying on a visually brightest amplitude slice. A framework combining fixed-region-of-interest analysis, numerical phantom analysis, and multiple image metrics was developed for rapid eTC-PCT imaging of vascular-like structures in the intact mouse head. Full delay-sequence analysis was performed on three independently acquired in vivo datasets, one from each animal. Each dataset contained 593 correlated amplitude slices. Maximum contrast-to-noise ratio (CNR) reached 3.13 at 710 ms, whereas apparent FWHM increased from approximately 12.4 to 23.6 pixels across the identifiable delay range. The minimum eye-to-target response ratio occurred at a delay with reduced CNR. Numerical absorbing-tube phantom analysis further showed that delay-resolved maps should be interpreted through detectability and diffusion-broadened apparent width, rather than as uncalibrated geometric depth sections. A 14 s acquisition reduced imaging time to 17.3% of an 81 s reference, corresponding to a 5.79-fold acceleration and a relative dose of 0.173 under matched exposure. The 0.2–0.6 Hz, 0.1 s, and 14 s protocol is, therefore, considered a practical option under the present experimental conditions rather than a universal optimum. Overall, eTC-PCT parameter selection requires a multi-metric trade-off among CNR, apparent FWHM, boundary gradient, anatomical interference, acquisition time, and exposure.