Open Access

Skin layer classification by feedforward neural network in bioelectrical impedance spectroscopy

Kiagus Aufa Ibrahim
Kiagus Aufa Ibrahim
, 
Marlin Ramadhan Baidillah
Marlin Ramadhan Baidillah
, 
Ridwan Wicaksono
Ridwan Wicaksono
 and 
Masahiro Takei
Masahiro Takei
   | Aug 10, 2023
Journal of Electrical Bioimpedance's Cover Image
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Published Online: Aug 10, 2023
Page range: 19 - 31
Received: Jul 04, 2023
Accepted: Aug 05, 2023
DOI: https://doi.org/10.2478/joeb-2023-0004
Keywords
© 2023 Kiagus Aufa Ibrahim et al., published by Sciendo
This work is licensed under the Creative Commons Attribution 4.0 International License.

Fig.1:

Schematic flow of skin layer classification of conductivity change
Schematic flow of skin layer classification of conductivity change

Fig. 2:

Electrical properties of skin, fat, and muscle.
Electrical properties of skin, fat, and muscle.

Fig. 3:

Nyquist plot based on numerical simulation of φs in the Δσ and D/H < 1 in all frequency range.
Nyquist plot based on numerical simulation of φs in the Δσ and D/H < 1 in all frequency range.

Fig. 4:

DRT results based on simulation of φs in the case of D/H < 1 in all frequency range.
DRT results based on simulation of φs in the case of D/H < 1 in all frequency range.

Fig. 5:

The comparison of FNN results related to feature extraction of αξ effect on bipolar and tetrapolar.
The comparison of FNN results related to feature extraction of αξ effect on bipolar and tetrapolar.

Fig. 6:

The comparison of FNN results related to feature extraction of αξ effect on bipolar and tetrapolar using four matrices profile.
The comparison of FNN results related to feature extraction of αξ effect on bipolar and tetrapolar using four matrices profile.

Fig. 7:

Experimental setup conditions with porcine skin.
Experimental setup conditions with porcine skin.

Fig. 8:

DRT results based on experiment with φs = Bipolar in all frequencies.
DRT results based on experiment with φs = Bipolar in all frequencies.

Fig. 9:

DRT results based on experiment with φs = Tetrapolar in all frequencies.
DRT results based on experiment with φs = Tetrapolar in all frequencies.

Fig. 10:

The confusion matrix shows the highest validation accuracy of experiments of porcine skin with FNN and four impedance inputs αξ.
The confusion matrix shows the highest validation accuracy of experiments of porcine skin with FNN and four impedance inputs αξ.

Fig. 11:

Comparison of sensitivity map distribution: bipolar and tetrapolar.
Comparison of sensitivity map distribution: bipolar and tetrapolar.

Experimental conditions

Configuration parameter Measurement parameter
Injection pattern φs Electrode length ratio to skin thicknessδb Conductivity-changed layeryp ConcentrationCNacl [mM] Frequency pair frlh$$f_{r}^{lh}$$ [kHz]

I. Bipolar

II. Tetrapolar

D/H < 1, D/H = 1, D/H > 1

 Dermis (D) only

c1 = 15

c2 = 20;

c3 = 25;

c4 = 30;

c5 = 35;

 f1lh=2&10;f2lh=2&35;f3lh=2&100;f4lh=2&225;f5lh=10&35;f6lh=10&100;f7lh=10&225;f8lh=35&100;f9lh=35&225;f10lh=100&225$$\begin{array}{*{35}{l}} f_{1}^{lh}=2\And 10; \\ f_{2}^{lh}=2\And 35; \\ f_{3}^{lh}=2\And 100; \\ f_{4}^{lh}=2\And 225; \\ f_{5}^{lh}=10\And 35; \\ f_{6}^{lh}=10\And 100; \\ f_{7}^{lh}=10\And 225; \\ f_{8}^{lh}=35\And 100; \\ f_{9}^{lh}=35\And 225; \\ f_{10}^{lh}=100\And 225 \\ \end{array}$$

Comparison studies of skin condition detection using only BIS or combined with machine learning algorithm.

No Author Skin Condition Machine Learning Algorithm & Data Features Frequency Pair Selection & Reason Injection Patterns
1 Stig Ollmar [18] Oral mucosa NA & Ź, Θ´$${\Theta }'$$, Ŕ, and X′ $${X}'$$ 20 [kHz] & 50 [kHz]: NA Bipolar
2 Nicander et al. [7] Irritant dermatitis NA & Ź 20 [kHz] & 1 [MHz]: NA Bipolar
3 Ramos & Bertemes-Filho [36] Skin cancer NA & Electrical equivalent circuit 100 [Hz] – 1 [MHz]:To analyze the tetrapolar probe’s sensitivities’ frequency response. It was discovered that frequency has little effect on sensitivity. Tetrapolar
4 Ferreira et al. [37] Skin irritation NA & Resistance ratio from two depth locations 20 [kHz] & 50 [kHz]:The ratio of total skin impedance obtained at low (20 [kHz]) and high frequencies (500 [kHz]) is the basis of the irritation indices. Bipolar
5 Gessert et al. [12] Skin melanoma CNN and SVM & Ź and Images 1 [kHz] − 2.5 [MHz]:Following the device’s frequency range. Bipolar
6 Luo et al. [38] Skin cancer NA & Transversal and longitudinal of relative permittivity and conductivity 8 – 256 [kHz]:For measurements of lesional and normal skin, intraclass correlation coefficient (ICC) conductivity values were low at 8 and 16 [kHz]. In contrast, relative permittivity ICC results displayed excellent repeatability at 16 [kHz]. Tetrapolar
7 Sarac et al. [39] Skin cancer NA & EIS Score 1 [kHz] – 2.5 [MHz]:The extracellular environment affects resistance to low frequencies, whereas both the intracellular and extracellular environments influence readings at higher frequencies. Bipolar
8 This study Skin layer classification FNN & α|Z|, αθ, αR, and αX frlh$$f_{r}^{lh}$$ are selected based on DRT results. Bipolar, Tetrapolar

Comparison of FNN accuracy Acc in terms of variation of frequency pair selection from experiment results.

Frequency pair frlh$$f_{r}^{lh}$$ [kHz] Bipolar Acc [%] Tetrapolar Acc [%]
f1lh=2&10$$f_{1}^{lh}=2\And 10$$ 44.1 1.2
f2lh=2&35$$f_{2}^{lh}=2\And 35$$ 80.6 17.6
f3lh=2&100$$f_{3}^{lh}=2\And 100$$ 56.5 16.5
f4lh=2&225$$f_{4}^{lh}=2\And 225$$ 40.6 10.0
f5lh=10&35$$f_{5}^{lh}=10\And 35$$ 88.8 90.0
f6lh=10&100$$f_{6}^{lh}=10\And 100$$ 90.6 84.1
f7lh=10&225$$f_{7}^{lh}=10\And 225$$ 61.2 32.4
f8lh=35&100$$f_{8}^{lh}=35\And 100$$ 60.6 90.6
f9lh=35&225$$f_{9}^{lh}=35\And 225$$ 55.3 25.3
f10lh=100&225$$f_{10}^{lh}=100\And 225$$ 68.2 23.5

Parameters for training data set

Configuration parameter Measurement parameter
Injection pattern φs Electrode-length-to-skin-thickness ratio δb Conductivity-changed layer ψp Conductivity change Δσq [%] Frequency pair frlh$$f_{r}^{lh}$$ [kHz]

I. Bipolar

II. Tetrapolar

D/H < 1, D/H = 1, D/H > 1

Fixed electrode gap:

dg = 1 [mm]

Variable electrode diameter:

de = {1, 2, 3}[mm]

Electrode length:

D = dg + de

Fixed each layer thickness:

hS = 50 [μm], hE = 0.45 [mm],

hD = 2.5 [mm], hF = 5 [mm]

Fixed skin thickness:

H = hS + hE + hD + hF

ψ1 = Stratum Corneum only (S)

ψ2 = Epidermis (E) only

ψ3 = Dermis (D) only

ψ4 = Fat (F) only

ψ5 = S + E

ψ6 = E + D

ψ7 = D + F

ψ8 = S + E + D

ψ9 = E + D + F

ψ10 = S + E + D + F

Δσ1 = −20

Δσ2 = −17.5

Δσ3 = −15

Δσ4 = −12.5

Δσ5 = −10

Δσ6 = −7.5

Δσ7 = −5

Δσ8 = −2.5

Δσ9 = 0

Δσ10 = 2.5

Δσ11 = 5

Δσ12 = 7.5

Δσ13 = 10

Δσ14 = 12.5

Δσ15 = 15

Δσ16 = 17.5

Δσ17 = 20

 f1lh=2&10f2lh=2&35f3lh=2&100f4lh=2&225f5lh=10&35f6lh=10&100f7lh=10&225f8lh=35&100f9lh=35&225f10lh=100&225 $$\begin{array}{*{35}{l}} f_{1}^{lh}=2\And 10 \\ f_{2}^{lh}=2\And 35 \\ f_{3}^{lh}=2\And 100 \\ f_{4}^{lh}=2\And 225 \\ f_{5}^{lh}=10\And 35 \\ f_{6}^{lh}=10\And 100 \\ f_{7}^{lh}=10\And 225 \\ f_{8}^{lh}=35\And 100 \\ f_{9}^{lh}=35\And 225 \\ f_{10}^{lh}=100\And 225 \\ \end{array}$$

Matrix profile of αξ

Matrix Profile Number of input features αξ Details
One matrix 4 Z´,θ´,R´,X´$${Z}',{\theta }',{R}',{X}'$$
Two matrices 6 Z´+θ´,Z´+R´,Z´+X´,θ´+R´,θ´+X´,R´+X´$${Z}'+{\theta }',{Z}'+{R}',{Z}'+{X}',{\theta }'+{R}',{\theta }'+{X}',{R}'+{X}'$$
Three matrices 3 Z´+θ´+R´,Z´+θ´+X´,θ´+R´+X´$${Z}'+{\theta }'+{R}',{Z}'+{\theta }'+{X}',{\theta }'+{R}'+{X}'$$
Four matrices 1 Z´+θ´+R´+X´$${Z}'+{\theta }'+{R}'+{X}'$$
eISSN:
1891-5469
Language:
English
Publication timeframe:
Volume Open
Journal Subjects:
Engineering, Bioengineering and Biomedical Engineering, Biomedical Electronics, Life Sciences, Biophysics, Medicine, Biomedical Engineering, Physics, Spectroscopy and Metrology
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