4 Experimental Results
4.4 Transmission Spectroscopic Information of Hemoglobin
Fig. 4.16 is the transmission waveform of Hemoglobin (Hb) samples. THz radiation amplitude is decreased to about half of the reference THz waveform in case of the thin sample (320µm and 350µm).
It is decreased to about 1/3 in case of the thick sample (960µm). Fig. 4.17 shows the FFT spectrum. Transmission spectrum amplitude is also larger in thin sample compared with the thick sample. Broadband absorption from 0.4THz to 2.0 THz has been observed in these deoxy-Hb samples.
No special absorption line is found for powder or thin film hemoglobin, while broadband absorption from 0.4 to 2.0 THz is observed. THz transmittance spectrum of these Hb samples is calculated from spectrum amplitude of samples divided by the reference one, which is shown in Fig.
4.18. The transmission efficiency of thin Hb samples is gradually decreased as frequency increased which similar as the blood. However, it is dramatically decreased after 0.4THz in case of thick sample. It is even decreased to almost 0 after 1.4THz, which represents the strong absorption. In Fig. 4.19, the refractive index of powder and thin film sample is obvious different. Refractive indices of powders and thin film are from 1.88±0.01 to 1.83±0.01 and 1.73±0.05 to 1.60±0.05 with respectively from 0.2TH to 1.2THz. These are smaller than the blood case [15]. In Fig. 4.18, absorption coefficient of powders and thin film are from 3cm-1 to 33cm-1 and 8cm-1 to 39cm-1 with respectively from 0.2TH to 1.2THz. It is obviously smaller than value blood because of the less content of water absorption in these dry deoxcy-Hb samples.
Fig. 4.16 Waveform of transmitted THz signal
6 8 10 12 14 16 18
-1.0 -0.5 0.0 0.5 1.0 1.5
2.0 Reference
Hemoglobin (powder-320µm) Hemoglobin (Thin film-350µm) Hemoglobin (powder-960µm)
Amplitude (10-4 V)
Time(ps)
0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8
0.0 5.0x10-8 1.0x10-7 1.5x10-7
Reference
Hemoglobin (powder-320µm) Hemoglobin (Thin film-350µm) Hemoglobin (powder-960µm)
Amplitude (a.u.)
Frequency (THz)
Fig. 4.18 Transmittance of THz signal through hemoglobin
Fig. 4.19 Refractive index of hemoglobin from 0.2 THz to 1.2 THz
0.2 0.4 0.6 0.8 1.0 1.2
1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 2.1
Hemoglobin (powder-320µm) Hemoglobin (Thin film-350µm) Hemoglobin (powder-960µm)
Refractive index (n)
Frequency (THz)
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0.0
0.2 0.4 0.6 0.8
1.0 Hemoglobin (powder-320µm)
Hemoglobin (Thin film-350µm) Hemoglobin (powder-960µm)
Transmittance
Frequency(THz)
Fig. 4.20 Absorption coefficient of hemoglobin from 0.2 THz to 1.2 THz
4.5 Determination of Interface of Stacked Porcine Skins
From the experimental results of section 4.1 and section 4.2, the refractive indices of normal and burned porcine skins are different. This characteristic difference between normal and burned porcine skins makes it possible to detect the interface between burned and normal part of a partial burned skin. If the interface exists, wave propagates in the skin will be reflected and reflected signal can be detected to make sure the existence of burned-normal interface.
The reflected THz radiation of two layers porcine skins (burned porcine skin + normal porcine skin) is measured. The two layer structure
0.2 0.4 0.6 0.8 1.0 1.2
0 20 40
60 Hemoglobin (powder-320µm)
Hemoglobin (Thin film-350µm) Hemoglobin (powder-960µm))
Absorption coeffecient (cm-1 )
Frequency (THz)
is applied to simply model the partially burned skin.
4.5.1 Reflected THz Waveform of One Layer of Porcine Skin
The reflected THz radiation of a normal porcine skin and a burned porcine skin is measured. The thicknesses of these two porcine skins are listed in Table 4.2.
Normal Burned
Thickness 0.27mm 0.53mm
Table 4.2 Thickness of porcine skins
Fig. 4.21 shows the expected conformation of the reflected THz waveform form single porcine skin. The measured waveform will be the superposition of the first and second reflected waveform.
porcine skin measured waveform
Incident THz wave
Second reflected wave First reflected wave
Fig. 4.21 Schematic of reflected THz waveform
From the measured results shown in Fig. 4.22 and Fig. 4.23, the reflected waveform is as expected as in Fig. 4.21. The times of flight
from first reflection to second reflection are 3.0 ps and 6.2 ps. The reflective indices of the normal and burned porcine skins are about 1.67 and 1.75 respectively.
0 10 20
-0.8 -0.4 0.0 0.4 0.8
Normalized amplitude
Time(ps) Ref
Normal porcine skin first reflection
second reflection
Fig. 4.22 The reflected waveform of normal porcine skin
0 10 20
-0.8 -0.4 0.0 0.4 0.8
Normalized amplitude
Time(ps) Ref
Burned porcine skin first reflection
second reflection
Fig. 4.23 The reflected waveform of burned porcine skin
4.5.2 Reflected THz Waveform of Two Layers of Stacked Porcine Skins
The normal and burned porcine skins are stacked to form the two layer structures. Fig. 4.24 shows the expected conformation of the reflected waveform from two stacked layers.
Normal porcine skin
Burned porcine skin
Incident THz wave
First reflected wave
Second reflected wave
Third reflected wave measured waveform
Fig. 4.24 The Schematic of reflected THz waveform
In Fig. 4.25, the first, second and third reflection THz waveforms are distinguished. The times of flight from first reflection to second reflection and second reflection to third reflection are 5.7 and 3.2 ps, which give the depth information about 488µm and 287µm respectively.
The values of time of flight are very close to the results in section 4.5.1.
There are several tenth µm of thickness differences in comparison with the measured thickness. The deviations of time of flight and thickness may caused from the surface of porcine is not very flat. The depth information of a simple burned-normal interface is detected from the measurement result.
0 10 20 30 40 50 -0.8
-0.4 0.0 0.4 0.8
Normalized amplitude
Time(ps)
Ref 2 layers first reflection second reflection third reflection
Fig. 4.25 The reflected waveform of two layers of stacked porcine skins
5. Conclusions and Future Works
In conclusion, the porcine skin has broadband absorption from 0.2 to 1.2THz. Difference in refractive indices of normal and burned porcine skins is found. The refractive index of normal porcine skin is from 1.77±0.01 to 1.66±0.01, which is smaller than the refractive index of burned porcine skin form 1.81±0.02 to 1.70±0.02 from 0.2THz to 1.0 THz. The absorption coefficients of normal and burned porcine skins are close. Furthermore, the reduction of birefringence between normal and burned porcine skin is observed. In addition, the spectroscopy of powder and thin-film hemoglobin is measured. Broadband absorption from 0.4THz to 2THz has been observed in hemoglobin samples. Refractive indices and absorption coefficients of hemoglobin have been demonstrated from 0.2THz to 1.2THz, which is important for the hemoglobin related biomedical-optics. Further reflective type measurement of the stacked burned and normal porcine skins for simulating partial burned biological skin can be implemented by THz -TDS. The waveform of THz radiation reflected from the surface, interface and back of the stacked structure of burned and normal porcine skins are resolved. Time of flight matched well with the original reflected waveform of normal and burned porcine skin. Clinical burned depth detection will be possible from these initial experiments.
In the future, THz-TDS will be further applied to the reflective type measurement of partial burned porcine skin to obtain the depth information. In addition, the spectroscopy of HbO2 in the THz region will be measured.
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