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

Figures

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  Fig. 1. SDS-dependent spectral morphologies of ex vivo porcine left ventricular epicardium. Normalized relative reflectance spectra with their derivatives are shown for SDS = 1 mm (A, E), 2 mm (B, F), 4 mm (C, G), and 6 mm (D, H). A - D: Mean spectra (solid) with 95% confidence intervals (shaded) for lesions of depth > 4 mm, lesions ≤ 4 mm, where 4 mm was used as a practical cutoff for visualization and OI development, together with adipose and untreated epicardial muscle; E - H: The corresponding first-order derivative spectra.

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  Fig. 2. Ex vivo ROC-based evaluation of LOIs and ACIs across SDS. ROC curves and corresponding AUC values are shown for lesion versus non-lesion differentiation using the LOI at SDS = 1 mm (A), 2 mm (B), 4 mm (C), and 6 mm (D), and for adipose versus non-adipose differentiation using the ACI at SDS = 1 mm (E), 2 mm (F), 4 mm (G), and 6 mm (H).

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  Fig. 3. Ex vivo depth- and transmurality-sensitive behavior of the selected optical indices. A-D: Index means across 1-mm lesion-depth bins for SDS = 1, 2, 4, and 6 mm. E-H: The same indices across 10% lesion-ratio bins as an indicator for transmurality. Red points represent bin-averaged index values, with variability shown as the mean ± standard deviation (SD) (horizontal and vertical error bars). The blue lines indicate linear fits to the means, along with R² and slope β values reported. “ns” denotes pairwise comparisons between selected lesion-depth bins that were not statistically significant (p > 0.05).

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  Fig. 4. Representative quantitative ex vivo lesion-depth prediction using multi-SDS side-viewing NIRS. A: Gross image of an excised left ventricle with multiple RFA lesions. B: Registered lesion-depth ground truth reconstructed from gross-section measurements. C: Raw lesion-depth prediction generated by the regression model. D: Lesion-probability mask generated by the classification model. E: Final masked lesion-depth prediction obtained after suppressing predictions in non-lesion regions. F: Absolute prediction error relative to the reconstructed lesion-depth ground truth.

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  Fig. 5. Overview of the side-viewing NIRS mapping probe design and EM tracking integration. A: Model of the 3D-printed probe with grooves on the underside to secure optical fibers. Inset: enlarged distal-tip cross-section showing angle-polished fiber (≈ 45°), reflective coating, clear epoxy, and the EM tracking probe mounted on the back side of the paddle. The arrow indicates the representative ray path. B: Photograph of the probe tip demonstrating the positions of the side-viewing multimode fibers and the SDS used for spectral acquisition.

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  Fig. 6. Characterization of the side-viewing fiber through simulation and experiment. A: Zemax simulation of the side-viewing fiber, showing the diverging light pattern at the angled tip. An epoxy block (n = 1.66) was added to replicate the real probe. B - E: Experimental beam profiles of a side-viewing fiber at varying distances (0.0 to 0.5 mm) from the probe tip, demonstrating good agreement with the simulation. Blue lines represent the measured intensity profiles, while red lines indicate Gaussian fits to the experimental data.

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  Fig. 7. Monte-Carlo simulation of SDS-dependent penetration depth. A: Detected-photon pathway maps for SDS from 1 to 6 mm, shown on a log scale. The colorbar represents the voxel-wise contribution to the detected signal. Triangles mark the positions of the source and detector fibers. The red dashed line marks the central axis; horizontal dashed lines indicate 3 dB (yellow), 10 dB (green), and 15 dB (magenta) penetration depths. Blue curves show the central-axis profiles and red curves the corresponding log-normal fits. B: Penetration depth versus SDS, showing deeper sampling with increasing SDS.

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  Fig. 8. Workflow for LV lesion creation, NIRS mapping, and ground-truth generation. The left ventricle was dissected, and irrigated RFA lesions were created in 37 °C PBS, after which ex vivo NIRS mapping was performed using the EM-tracked side-viewing probe. Lesions were subsequently TTC-stained, bisected, and photographed next to a ruler. From these images, lesion depth was quantified as a function of radial distance from the lesion center, assuming the lesions were centrally symmetric. Finally, the measurements were assembled into ground-truth lesion-depth maps.