Side-viewing probe for lesion depth mapping on the left ventricle epicardium with near-infrared spectroscopy

Epicardial radiofrequency ablation can fail when lesions are not sufficiently deep or transmural, yet intraoperative feedback remains largely indirect. This study presents a fiber-based, side-viewing near-infrared spectroscopy (NIRS) probe with multiple source-detector separations (SDS) to enable depth-sensitive mapping of lesions on the porcine left-ventricular epicardium. Monte Carlo simulations predicted progressively deeper sampling with increasing SDS, motivating the use of multi-separation acquisition for depth-resolved contrast. Experiments were performed on 11 porcine hearts with 133 irrigated epicardial lesions spanning a wide depth range, with lesion depth ground truth reconstructed from post-stain gross section measurements. SDS-dependent spectral signatures were observed across lesions with depths greater than 4 mm, lesions with depths ≤ 4 mm, adipose tissue, and untreated epicardial muscle, and optical indices capturing these patterns were identified for lesion and adipose classification, as well as for lesion-depth sensitivity. Lesion and adipose indices achieved strong receiver operating characteristic (ROC) performance across SDS (lesion AUC 0.87-0.91; adipose AUC 0.94-0.97), and depth-sensitive indices exhibited monotonic trends with lesion depth (R² up to 0.97). Applying a random forest lesion mask enabled depth-sensitive maps that were consistent with variations in the ground truth.