Pixel-Level Quantification of Subcutaneous Shear-Wave Velocity Heterogeneity for Grading Lymphatic Obstruction in Breast Cancer-Related Lymphedema
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Objectives
To develop and validate pixel data analysis (PDA) for reconstructing pixel-level shear-wave velocity (SWV) from saved Holder-Optimized Elastography (HOE) elastograms and to determine whether whole-field subcutaneous heterogeneity provides a quantitative signature of lymphatic obstruction compared with visual high-velocity-area (HVA) counting and sparse manual region-of-interest (ROI) sampling.
Materials and Methods
In this cross-sectional study, 110 women after breast cancer surgery underwent lymphoscintigraphy and HOE, a pressure-minimized acquisition framework that preserves conventionally captured SWV information while additionally revealing spatial abnormalities attenuated by handheld acquisition. Reconstruction validation used 200 paired ROIs, spanning nearly the full displayed SWV range, from 49 images retrieved from the picture archiving and communication system; reproducibility was assessed across 96 matched anatomical sites from 6 participants undergoing independently reacquired HOE examinations. PDA, visual HVA counting, and manual ROI sampling were evaluated on the same HOE-acquired elastograms in task-specific common complete-case cohorts.
Results
PDA reconstructed the machine-reported SWV with near-zero error over a range of 1.17 - 9.97 m/s (mean difference, +0.0009 m/s; mean absolute error, 0.0075 m/s; 95% limits of agreement, -0.0202 to +0.0221 m/s). For subcutaneous variance, interobserver/intraobserver intraclass correlation coefficients were 0.709/0.799 for PDA and 0.178/0.560 for manual ROI sampling. In the primary no obstruction versus partial obstruction comparison (n = 93), forearm-pooled PDA subcutaneous variance ratio yielded the highest observed area under the curve (AUC, 0.858; 95% confidence interval, 0.771 – 0.946), compared with 0.820 for visual HVA counting and 0.794 for manual ROI sampling. PDA’s subcutaneous variance ratio remained a leading feature across all three comparisons (AUC, 0.858 – 0.878), including partial versus total obstruction grading, where all three frameworks showed high discrimination.
Conclusions
PDA accurately reconstructs pixel-level SWV from saved HOE elastograms and enables reproducible whole-field quantification of superficial shear-wave elastography heterogeneity. Subcutaneous variance ratio was the leading quantitative PDA feature across lymphatic-obstruction comparisons and was particularly informative in partial obstruction. The same approach also enables retrospective quantitative reanalysis of compatible archived elastograms.
Plain-Language Summary
Pixel data analysis (PDA) reconstructs quantitative pixel-level shear-wave velocity from saved superficial elastography images, allowing the complete measurable color field to be analyzed rather than a few manually sampled regions. Reconstructed values closely matched machine measurements, and whole-field subcutaneous variance was substantially more reproducible than manual ROI sampling. Subcutaneous variance ratio remained a leading diagnostic signal across obstruction severities, including in partial obstruction without visually detectable high-velocity areas.
