Quantitative measurement of cutaneous neurofibromas in neurofibromatosis type 1 using a structured-light scanner

Cutaneous neurofibromas (cNF) are found in >99% of adults with neurofibromatosis type 1 (NF1) and are a hallmark feature of the disorder. Due to the large number, varying sizes, and irregular distribution of the tumors, quantification is hardly possible for most cases. We introduce a novel structured-light scanner to address this issue.

This NF-scanner captures the three-dimensional (3D) geometry of neurofibromas in patients and calculates the number, area, and volume of the tumors over the whole body. The measuring time is about 7 minutes for most cases. Validation was performed on 100 model neurofibromas (hemispheres, diameters 6-20 mm) affixed to a standardized torso model in two spatial distributions (evenly distributed and clustered), with five repeated measurements per configuration. Subsequently, the scanner was applied to 16 patients with NF1 (eight male and eight female; age range, 19-69 years), each undergoing three to six repeated whole-body scans. Intra-individual measurement variability was quantified using coefficients of variation, and the correlation of tumor burden parameters with age was assessed using Spearman's rank correlation.

Testing on modelled neurofibromas demonstrated reproducibility for number and area measurements. For evenly distributed model neurofibromas, the scanner detected a mean count of 131 (true value: 100; overestimation approximately 31%), with measured total area and volume corresponding to 96% and 65% of the true values, respectively. For clustered model neurofibromas, mean detection yielded 83.8 lesions (approximately 16% underestimation), with total area and volume at approximately 80% and 53% of ground truth. Clinical application in 16 patients confirmed the expected correlations of age with number, total area, and total volume of the tumors. Neurofibroma counts ranged from 500 to more than 2,700 per individual. Tumor number, total area, and total volume all showed significant positive correlations with patient age. Intra-individual coefficients of variation were lowest for tumor count and highest for total volume, indicating that surface-based parameters are more robustly reproducible than volumetric estimates with the current analysis pipeline.

The NF-scanner enables quantification of neurofibromas in a large number of patients, and therefore contributes to improving clinical documentation and clinical research. Tumor count and total area measurements demonstrated acceptable reproducibility, whereas volumetric assessments showed greater variability, consistent with findings from comparative studies of other 3D imaging systems. With further refinement of the analysis software, the structured-light NF-scanner offers a scalable, contact-free approach for objective whole-body quantification of cNF burden, suitable for both clinical documentation and interventional research.