Fig 1.
Schematic illustration of the Nimble with all components.
The aspiration probe is connected (tubes T1 and T2) to pressure sensors PS1 and PS2 via filters 1 and 2. T1 is connected to a peristaltic pump, which generates the progressive negative pressure in the cavity. The valve releases the pressure at the end of the measurement.
Fig 2.
(A) Schematic of aspiration probe: The position of the vertical tube T1 defines the elevation height h. (B) The tissue is drawn into the cavity until it closes T1. (C) The dimensions of the aspiration probe are indicated.
Fig 3.
Output curve of Cutometer measurements.
Representative Elevation-Time curve (left) and Pressure-Elevation curve (right) of a Mode 2 Cutometer measurement. The maximum elevation is indicated with R0 and the loading and unloading curves are displayed. From the loading part of the Pressure-Elevation curve the closing pressure at 1 mm elevation is extracted for comparison with the Nimble parameter pclnimble. T0 and TR0 indicate the start of the experiment and the timepoint when R0 is reached respectively. These graphs were generated with a maximum suction pressure of 400 mbar.
Fig 4.
Output curve of Nimble measurements.
Representative Pressure-Time curve of a Nimble measurement for a defined elevation of 1.0 mm. Pressure measured by PS1 and PS2 are indicated. The closing pressure is recorded when Δp = 5 mbar is recognized.
Fig 5.
Influence of contact force on volar forearm.
Weight study with Nimble (A) and Cutometer (B) on human volar forearm. The grey blocks indicate added mass of each 20.0 g, corresponding to increased contact force; (C) shows results of measurements on volar forearm with the Cutometer (red) and the Nimble (blue), and corresponding FE calculations on skin (orange).
Fig 6.
Representation of the correction procedure.
(A) Cutometer measures tissue elevation from a baseline, defined by the apex of an initial deformation (response to contact force). (B) Nimble measures tissue elevation from skin surface (negligible initial deformation) due to its low weight. (C) The correction scheme accounts for this discrepancy and adds the Offset to the elevation measured by the Cutometer.
Table 1.
Analysis of the proposed correction scheme for Cutometer measurements.
Results of FE calculations with enforced initial deformation (corresponding to contact forces of 50 g and 100 g) are compared for closing pressure values before and after correction. Calculations were performed for skin.
Table 2.
Measurements on volunteer VO1.
Reported are mean data and standard deviation of repeated measurements by three observer (O1, O2 and O3) on the subject VO1 at four body locations (VF, FH, BH and LB). Data include the Offset Δ, the maximum elevation R0 and the closing pressure of Cutometer, and
of Nimble.
Table 3.
Measurements on volunteer VO2.
Reported are mean data and standard deviation of repeated measurements by three observer (O1, O2 and O3) on the subject VO2 at four body locations (VF, FH, BH and LB). Data include the Offset Δ, the maximum elevation R0 and the closing pressure of Cutometer, and
of Nimble.
Table 4.
Pearson correlation coefficient.
r and p-values, p, between stiffness values evaluated with Nimble (knimble) and Cutometer (kcuto and kR0).
Fig 7.
Mean stiffness and standard deviation for each location and subject.
(A) and (B): linear regression for a slope of 1.1 between mean stiffness kcuto and knimble (A) and corrected Cutometer data (B), for eight different skin locations. (C): standard deviation of stiffness measurements for each body location separated for two subjects (VO1 and VO2).
Fig 8.
Mean values and standard deviation of stiffness values kR0, kcuto, and knimble.
Values are shown for each location separated by subjects. Significant difference between locations measured by each device are indicated. Significance level are indicated as **p < 0.01 and *** p < 0.001.
Table 5.
Reliability of measurements with Cutometer (kR0 and kcuto, non-corrected and corrected), and Nimble (knimble).
Intraclass correlation coefficient reflects the ability of the parameter to differentiate among specimens in each subject (here: locations) with nVO1 = 36 and nVO2 = 72.
Fig 9.
Intraobserver variability in terms of linear dependency.
Linear dependency of stiffness values kR0, kcuto, knimble, and
based on repeated measurements at each location (VF, FH, BH and LB).
Table 6.
Coefficient of determination R2. R2 of intraobserver variability (in terms of linear regression) in stiffness values kR0, kcuto, knimble, and
based on repeated measurements at each location (VF, FH, BH and LB).
Fig 10.
Histogram plot of error between measurements of different observers (n = 3) for stiffness values kR0, kcuto, knimble, and
.
The error is defined as the percentage difference of each measured parameter with respect to the mean value for that sample. Root mean square (RMS) is indicated for each parameter (RMSR0 = 19%, RMScuto = 46%, RMSnimble = 24%, = 13% and
= 53%).
Fig 11.
Mean and standard deviation of Offset values in mm (measured by the Cutometer software).
Left: Mean Offset over all locations for each observer (O1, O2 and O3). Middle/Right: Mean Offset over all observers for each location (VF, FH, BH and LB) separated for two subjects (VO1 and VO2).