Fig 1.
(A) The physician performs the SPTs with a disposable multi-test on the surface of the forearm. (B) After 15 minutes, the physician measures the skin reactions or wheals using a ruler. (C) Typical shapes of wheals, from regular to irregular shape with pseudopod. (D) The wheal size assessment is approximated as an ellipse or by measuring the longest diameter.
Fig 2.
(A) 3D imaging system. (B) Captured fringe images. (C) 3D Reconstructions. The dotted red line denotes the overlapping region between the observation systems.
Fig 3.
Validation experiments: (A) measuring spherical caps of known diameters and (B) steps with known height.
Fig 4.
Block diagram illustrating the proposed method for the measurement of skin wheals.
S and D denote the 3D surface of the patient’s forearm and the estimated diameters, respectively. The other variables are intermediate outputs of every stage; their meaning is given in the text.
Table 1.
Measured diameters for six spherical caps with a caliper (Reference measurement) and the 3D imaging system (using camera 1 and camera 2). All values in millimeters.
Table 2.
Measured height for three steps from a reference step R0, using the camera 1 and the camera 2. All values in millimeters.
Fig 5.
The Global Surface Removal stage.
S and S′ denote the 3D surface of the patient’s forearm and the surface after removing the global curvature of the forearm, respectively. The other variables are intermediate outputs of every sub-stage; their meaning is given in the text.
Fig 6.
S′ and denote the surface after removing the global curvature of the forearm and the extracted surface patches, respectively. We have included the texture image to highlight the correct detection of the wheals. This image has been digitally sharpened to improve the visualization of the wheals.
Fig 7.
Custom user interface for the manual reference measurement of the wheal diameter.
Depth colorbar units in mm.
Fig 8.
The results of fitting a regular-shaped wheal with (A) the parametric model 1 and (B) the parametric model 2. Both models are in numerical agreement and slightly overestimate the reference measurement of 4.47 mm. For an irregular-shaped wheal the result from (C) parametric model 1 and (D) parametric model 2 differ by 0.44 mm. However, the result from parametric model 2 results in a more accurate estimation of the longest diameter.
Fig 9.
(A) Scatter plot, and (B) Bland-Altman plot of measured wheal diameter vs. estimated wheal diameter by the parametric model 2. The 95% agreement limits are [−1.58, 0.78] mm, which are close to the desired ±1 mm. (C) Scatter plot, and (D) Bland-Altman plot of measured wheal diameter vs. ruler-based measured diameter. Although, the mean difference is close to zero the 95% agreement limits are [−3.03, 2.91] mm, which are three times larger than the desired ±1 mm.
Table 3.
Results of the skin prick test.
Measurements are reported in millimeters.