Optical Monitoring of Tumors in BALB/c Nude Mice Using Optical Coherence Tomography

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  • ABSTRACT

    We report a method for optical monitoring of tumors in an animal model using optical coherence tomography (OCT). In a spectral domain OCT system, a superluminescent diode light source with a full width of 66 nm at half maximum and peak wavelength of 950 nm was used to take images having an axial resolution of 6.8 μ m. Cancer cells of PC-3 were cultured and inoculated into the hypodermis of auricle tissues in BALB/c nude mice. We observed tumor formation and growth at the injection region of cancer cells in vivo and obtained the images of tumor mass center and sparse circumferences. On the 5th day from an inoculation of cancer cells, histological images of the tumor region using cross-sectional slicing and dye staining of specimens were taken in order to confirm the correlation with the high resolution OCT images. The OCT image of tumor mass compared with normal tissues was analyzed using its A-scan data so as to obtain a tissue attenuation rate which increases according to tumor growth.


  • KEYWORD

    Optical coherence tomography , Tumor , Tissue attenuation , Mouse model

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  • [FIG. 1.] Spectral domain optical coherence tomography (OCT) with the schematic as in (a) was used for optical tomographic imaging of tumors. The superluminescent diode (SLD) light source has spectra with center wavelength of 950 nm and 3-dB bandwidth of 66 nm (b). FC: fiber coupler, BS: beam splitter, G: grating, M: reference mirror, S: galvano scanner, SO: signal output.
    Spectral domain optical coherence tomography (OCT) with the schematic as in (a) was used for optical tomographic imaging of tumors. The superluminescent diode (SLD) light source has spectra with center wavelength of 950 nm and 3-dB bandwidth of 66 nm (b). FC: fiber coupler, BS: beam splitter, G: grating, M: reference mirror, S: galvano scanner, SO: signal output.
  • [FIG. 2.] Spectral-domain OCT system performance was measured as the sensitivity of 82.2 dB at 0.1 mm deep position from a focal plane and the sensitivity roll-off rate of -48.9 dB/mm (a). Point spread function at 0.7 mm imaging depth shows an axial resolution of 6.6 mm (b). Sample attenuation of 29.6 dB was used for measuring sensitivities at various imaging depths.
    Spectral-domain OCT system performance was measured as the sensitivity of 82.2 dB at 0.1 mm deep position from a focal plane and the sensitivity roll-off rate of -48.9 dB/mm (a). Point spread function at 0.7 mm imaging depth shows an axial resolution of 6.6 mm (b). Sample attenuation of 29.6 dB was used for measuring sensitivities at various imaging depths.
  • [FIG. 3.] An in vivo cross sectional image was recorded throughout overall thickness of normal auricle in BALB/c nude mice by spectral domain OCT (a). Tissue layers such as epidermis, dermis, and cartilage are clearly shown in the magnified image (b) of the red rectangle. A-scan data obtained along the red line show the power levels at each tissue layer and in air (c). The signal level in blood vessel was found to be 3.9 dB lower than the minimum signal level in the other tissue regions. The point spread function (d) represents the axial resolution of 6.8 μ m which was measured at the interface between cartilage and dermis in the blue rectangle. The blue circles include blood vessels as in CCD images (lower (a)). Scale bar: 200 μ m.
    An in vivo cross sectional image was recorded throughout overall thickness of normal auricle in BALB/c nude mice by spectral domain OCT (a). Tissue layers such as epidermis, dermis, and cartilage are clearly shown in the magnified image (b) of the red rectangle. A-scan data obtained along the red line show the power levels at each tissue layer and in air (c). The signal level in blood vessel was found to be 3.9 dB lower than the minimum signal level in the other tissue regions. The point spread function (d) represents the axial resolution of 6.8 μ m which was measured at the interface between cartilage and dermis in the blue rectangle. The blue circles include blood vessels as in CCD images (lower (a)). Scale bar: 200 μ m.
  • [FIG. 4.] OCT images of an auricle region in BALB/c nude mice were taken in vivo before and after an injection of cancer cells into the hypodermis. Normal auricle tissues have the overall optical thickness of about 350 μ m in the image (a). Swollen auricle tissues are shown in tomographic image (b) and (c) on the 3rd and 5th days from an inoculation, respectively. The red arrow points out the gap of significant size on which actively growing tumor mass borders. Scale bar: 200 μ m (vertical), 400 μ m (horizontal).
    OCT images of an auricle region in BALB/c nude mice were taken in vivo before and after an injection of cancer cells into the hypodermis. Normal auricle tissues have the overall optical thickness of about 350 μ m in the image (a). Swollen auricle tissues are shown in tomographic image (b) and (c) on the 3rd and 5th days from an inoculation, respectively. The red arrow points out the gap of significant size on which actively growing tumor mass borders. Scale bar: 200 μ m (vertical), 400 μ m (horizontal).
  • [FIG. 5.] An OCT image of the tumor region is shown on the 5th day from an injection of cancer cells (a). The magnified image (b) of the red rectangle and the histological image (c) are arranged side by side so as to compare with each other. Tumor mass region is indicated with the dashed red line and pointed out by the red and black triangles. Blood vessels are shown around the tumor region as dark areas that have the lowest signal levels in the A-scan data of the tissue region. Scale bar: 200 μ m.
    An OCT image of the tumor region is shown on the 5th day from an injection of cancer cells (a). The magnified image (b) of the red rectangle and the histological image (c) are arranged side by side so as to compare with each other. Tumor mass region is indicated with the dashed red line and pointed out by the red and black triangles. Blood vessels are shown around the tumor region as dark areas that have the lowest signal levels in the A-scan data of the tissue region. Scale bar: 200 μ m.
  • [FIG. 6.] OCT images and A-scan data on 1st (before inoculation), 3rd and 5th days are shown in (a)-(d), (b)-(e) and (c)-(f), respectively. The A-scan data were brought from the OCT images at the position pointed out by the red triangle. The tomographic images and the A-scan data show that the tumor region has a strong rate of light attenuation compared to the normal tissues. Light attenuation is represented as a slope of the dashed red line that was linearly fitted to local maxima of signals from tissue interfaces.
    OCT images and A-scan data on 1st (before inoculation), 3rd and 5th days are shown in (a)-(d), (b)-(e) and (c)-(f), respectively. The A-scan data were brought from the OCT images at the position pointed out by the red triangle. The tomographic images and the A-scan data show that the tumor region has a strong rate of light attenuation compared to the normal tissues. Light attenuation is represented as a slope of the dashed red line that was linearly fitted to local maxima of signals from tissue interfaces.
  • [FIG. 7.] Attenuation constants of the normal tissue region are compared with those of the tumor tissue region as a function of day in a histogram. Filled circles represent averaged attenuation constants of the normal tissue region in the same image on the day. A tumor has more optical attenuation rate by a few hundred cm-1 than the surrounding normal tissues due to its dense vasculature.
    Attenuation constants of the normal tissue region are compared with those of the tumor tissue region as a function of day in a histogram. Filled circles represent averaged attenuation constants of the normal tissue region in the same image on the day. A tumor has more optical attenuation rate by a few hundred cm-1 than the surrounding normal tissues due to its dense vasculature.