Evaluation of Smartphones Equipped with Light Detection and Ranging Technology for Circumferential and Volumetric Measurements in Lower Extremity Lymphedema

Abstract

Lower extremity lymphedema (LEL) requires precise limb measurements for treatment evaluation and compression garment design. Tape measurement (TM) is the standard method but is time-consuming. Smartphones with light detection and ranging (LiDAR) technology may offer fast and efficient alternatives for three-dimensional imaging and measurement. This study evaluated the accuracy, reliability, and time efficiency of LiDAR measurements compared with those of TM in patients with LEL. A healthy volunteer and 55 patients were included. Circumferences of the foot, ankle, calf, knee, and thigh and the volume were measured using TM and smartphones with LiDAR. The water displacement method was used to validate volume measurements. The measurement time, reliability, correlation, agreement, and systematic differences between the methods were assessed. LiDAR showed excellent reliability in the healthy volunteer (inter-rater intraclass correlation coefficients: 0.960-0.988) and significantly reduced the measurement time compared with TM (64.0 ± 15.1 vs. 115.3 ± 30.6 s). In patients with LEL, strong correlations and agreements were observed for ankle, calf, and knee measurements. However, foot and thigh measurements showed lower correlations and larger discrepancies. LiDAR has excellent accuracy and reliability in measuring the circumference and volume of the lower leg and has the potential to reduce the time required to acquire data. Limitations include lower accuracy for foot and thigh measurements and the current workflow complexity, which requires the use of multiple software tools.

Keywords: LiDAR; circumference measurement; lymphedema; smartphones; volumetric measurement.

Figure 1

Schema at the time of measurement. The limb circumference is measured at the superior edge of the patella (knee), 10 cm above and below the patella (thigh and calf, respectively), the lateral malleolus (ankle), and the first and fifth metatarsal heads (foot) in the standing position. Vertical distances between the thigh and the knee (segment A), between the knee and the calf (segment B), and between the calf (segment C) and the ankle are measured using TM. Each segment is regarded as a circular truncated cone, and its volume is calculated. R and r: radii calculated based on the circumference, h: Height of the truncated cone.

Figure 2

3D images in the patient with lymphedema captured by the smartphone equipped with LiDAR on Metasequoia 4^®: (a) Clinical photograph (b) Front and (c) oblique views. The 3D image can be freely rotated in the software. (d) Measurement of the circumferential diameter in any cross section (unit: mm). LiDAR, light detection and ranging; 3D, three-dimensional.

Figure 3

Volume measurements and the time required for each measurement. (a) Box and whisker plot of the limb volume in a healthy volunteer. Each plot is obtained from a single measurement. The red square plot shows the volume determined using the water displacement method. (b) Box and whisker plots of the time required for each measurement. The time required for measurement by LiDAR is significantly shorter than that required by TM. LiDAR: light detection and ranging, TM: tape measurement.

Figure 4

Bland–Altman plots of LiDAR and TM data of all limbs. (a–h) Bland–Altman plots the measurements obtained from the foot, ankle, calf, knee, thigh, and the volume of segments A, B, and C, respectively. Dotted lines represent upper and lower limits of agreement, respectively. LiDAR: light detection and ranging, TM: tape measurement.

Figure 5

Bland–Altman plots of LiDAR and TM data of the affected limbs. (a–h) Bland–Altman plots the measurements obtained from the foot, ankle, calf, knee, thigh, and the volume of segments A, B, and C, respectively. Dotted lines represent upper and lower limits of agreement, respectively. LiDAR: light detection and ranging, TM: tape measurement.

Figure 6

3D images obtained by LiDAR. The acquired image is blurred and the boundary with the floor is unclear. 3D, three-dimensional; LiDAR, light detection and ranging.