Limb volumetry using an iPad-based three-dimensional scanner for assessment of edema

Objective

Quantifying limb edema is challenging owing to the lack of an easily accessible clinical technique. This study evaluates the reproducibility of an iPad-based three-dimensional (3D) scanning system for lower limb volumetry and identifies factors influencing measurement variability.

Methods

Twenty limbs from 10 healthy volunteers were scanned using an iPad-based Structure Sensor and software. Initial scans followed standard manufacturer instructions, but high variance rendered data unsuitable for clinical use. To improve accuracy, a standardized scanning protocol was developed, incorporating anatomical calibration, scanning distance standardization, and scanning time control. A 254-mm calf segment was defined using a 3D marker placed on the medial malleolus to ensure consistent volume measurement. The scanning distance was fixed between 50 and 59 cm to reduce zoom parallax errors, and scans were conducted after 3 pm to minimize diurnal volume fluctuations. Multiple technicians performed repeat scans on the same limb to assess intraobserver and interobserver scan reliability.

Results

Implementing the standardized protocol significantly decreased measurement variability. Defining a consistent anatomical scan region improved reproducibility, with the mean volume difference decreasing from 4.7% ± 3.6% to 2.1% ± 1.6%. Standardizing scanning distance reduced zoom-related errors, improving measurement consistency from 2.6% ± 1.5% to 2.0% ± 1.2% (P = .037). Time standardization further optimized accuracy, yielding a final mean volume difference of 1.8% ± 0.9%. No statistically significant differences were observed between measurements taken by different technicians (P > .05), demonstrating high interobserver reliability.

Conclusions

iPad-based 3D scanning provides a clinically reliable and cost-effective method of lower limb volumetry. The standardized protocol as described improves scan accuracy and reproducibility. Future studies should evaluate this method in a clinical population to validate its usefulness in disease assessment and progression tracking.