tầLữầ Realization of 3D image reconstruction from transillumination images of animal body ERE RURD 6 D 3D REBERO EL ACHE A EASE AE ET ICR TRAN TRUNG NGHIA # tl mt XA FORE lRi@SM2BfOSM tt (LS) # Tran Trung Nghia 4 li ầ x # Realization of 3D image reconstruction from transillumination images of animal body ( EMBREDS © 3D KBBMORE ) Three-dimensional (3D) imaging with X-ray or MRI has contributed greatly not only to medical diagnosis, but also to life science. The number of experimental animals killed for experimentation would be reduced if the animals 0 internal structures can be visualized non-invasively. In transil- lumination imaging using near-infrared (NIR) light, the location of internal bleeding, infection, and angiogenesis can be visualized. Functional imaging is also possible using spectroscopic principles.
With specific contrast media, the usefulness of NIR imaging is expanded significantly. However, the NIR transillumination technique has not been used widely. The major reason for that relative lack of use is the difficulty of the strong scattering in tissues. In transillumination images, the deeper structure is blurred and cannot be differentiated from the shallower and less-absorbing structure.
To overcome this problem, great effort has been undertaken to develop optical computed tomography (optical CT) techniques. The typical technique for a macroscopic structure is diffuse optical tomography (DOT). Using this technique, cross-sectional imaging of human breasts and infant heads was achieved. Once the cross-sectional images become available, 3D imaging is possible.
However, current techniques require great computational effort such as finite element method calculation, and large devices such as numerous fiber bundles around the object body. It would be possible to reconstruct the 3D structure with a common filtered back-projection algo- rithm and with a CCD or CMOS camera if the scattering effect in transillumination images can be suppressed effectively. They require much simpler and more compact device as well as much less computational effort. This study proposes the 3D imaging of internal absorbing structure of a small experimental animal from two-dimensional (2D) NIR transillumination images using new scattering suppression techniques.
This thesis presents the principle, implementation, and the results to show the feasibility of the proposed method. For scattering suppression, the deconvolution technique using the point spread function (PSF) is effective. In previous study, the PSF for the light source located inside the medium had been derived by applying the diffusion approximation to the equation of transfer. With a known depth of the light source in a diffuse medium, the light distribution can be recovered clearly through an interstitial tissue by the deconvolution with this PSF.
Therefore, realization of the 3D imaging from the transillumina- tion images can be expected if this light-source PSF can be applied to the transillumination image of light-absorbing structure. Through theoretical and experimental study, the applicability of the PSF for the light source to the transillumination images of the light-absorbing structure was confirmed. The effectiveness of this technique was also confirmed in the experiments with a tissue-equivalent phantom and animal tissue. The PSF is depth-dependent, and the technique explained above was applicable only for an object with known internal structure.
To expand the applicability of this technique, new algorithms were devised. An observed transillumination image is deconvoluted with the PSFs of different depths. Then the deconvoluted images are summed up to produce a new image that serves as a projection image in cross-sectional reconstruction. The projection image contains the projection of the true absorption dis- tribution and the incompletely deconvoluted projection as well.
To suppress the effect of this erroneous projection, an erasing process was devised. An initial cross-sectional image is reconstructed from the projection images obtained from many orientations. It is used as a template to erase the erroneous dis- tribution in the cross-section. After the application of this erasing process, a new improved projection image is formed in which the effect of the erroneous distribution is suppressed effectively.
Using the projections from many orientations obtained in this process, an improved cross-sectional image can be reconstructed. With the cross-sectional images at different heights, the 3D image can be reconstructed. The feasibility of the proposed technique was examined in a computer simulation and an experiment with a model phantom. The results demonstrated the effectiveness of the proposed technique.
Finally, the applicability of the proposed technique to a living animal was examined. An anesthetized mouse was fixed in a transparent cylinder. To produce a transillumination image of good quality, a light trap in the cylinder was devised. Using the proposed technique, the 3D structure of the mouse abdomen was reconstructed.
High-absorbing organs such as the kidneys and parts of the liver became visible. Results of this study suggest that a new optical CT having different features from those of currently available techniques is possible. This simple system can provide a cross-sectional image and recon- struct the 3D structure of internal organ in the mouse body. It can provide a useful and safe tool for the functional imaging of internal organs of experimental animals and for optical CT imaging of the near-surface structure of a human body.
Table of contents Contents Table of contents i tA List of figures List of figures Fig. Small animal imaging modalities with typical instruments available and illustrative example images that can be obtained with these modalities: (a) micro-PET, (b) micro-CT, (c) micro-SPECT, (d) micro-MRI, (e) optical reflectance fluorescence imaging, (f) optical bioluminescence iMagiN. Scanning geometry: (a) rotation bed, (b) rotation gantry. Small animal computed tomography (CT): (a) schematic illustrating the principles of CT, (b) small animal CT axial images and 3D representation of tumor volumes in a genetically engineered mouse model of non-small-cell lung cancev.
Small animal magnetic resonance imaging (MRI): (a) schematic showing the basic principles of this technique, (b) Cross-sectional MRI images of the mouse, whereby the tumor 1s highlighted wIth an aTYOW. cv vn ren 9 Fig. Small animal positron emission tomography (PET): (a) schematic illustrating the basic principles of PET, (b) images demonstrating the noninvasive visualization of an orthotopic brain tumor in a rat. Pinks arrows show the tumor, and the red arrow shows wound due to intracerebral implantation of tumor celÌs.
Small animal single photon emission computed tomography (SPECT): (a) schematic illustrating the principles of SPECT, (b) SPECT images demonstrating the utility of visualizing gastrin-releasing peptide receptor in mice. Arrows point to tumor. Optical fluorescence molecular imaging: (a) schematic illustrating the principle of molecular imaging using optical fluorescence, (b) fluorescence images. Optical bioluminescence molecular imaging: (a) schematic illustrating the principle of molecular imaging using optical bioluminescence, (b) bioluminescence ¡2T TT.
Small animal imaging using diffuse optical tomographyy. The absorption spectra oŸ maJor tissue chromophores. Schematic rendering of different methods that can be used for whole-body fluorescence imaging: (a) broad beam illumination, (b) raster-scan illumination, (c) raster-scan illumination, (d) broad beam transillumination, (e) raster-scan transillumination, (f) raster-scan transillumination. The configurations optimized for 11 List of figures tomography imaging and fiber-based planar configurations are not shown in this Fig.
The three imaging domains of optical imaging system: (a) continuous wave domain, (b) frequency domain, (c) time domaïn.- ¿2 ¿5c 22222 S2S£eE+t+tztzxeeexes 20 Fig. X-ray CT views. Computed tomography acquires a set of views and then reconstructs the corresponding image. Each sample in a view is equal to the sum of the image values along the ray that points to that sample.
In this example, the image is a small pillbox surrounded by zeroes. While only three views are shown here, a typical X-ray CT scan uses hundreds of views at slightly different angles. Example of simple back-projection. Back-projection reconstructs an image by taking each view and smearing it along the path it was originally acquired.
The resulting image is a blurry version of the Correct image. The Fourier slice theorem relates the Fourier transform of a projection to the Fourier transform of the object along a radial line.- --+++sss++cssxcseeeseeesss 31 Fig. The ideal filter response for filtered back-projection. Solid line: the Ram-Lak filter frequency response.
Dashed line: resulting frequency response of the Ram-Lak filter multiplied by the Hamming function.-- - c n1 vn vn ren 34 Fig. Example of using filtered back-projection technique. Filtered back-projection is reconstructing an image by filtering each view before back-projection. This removes the blurring seen in the simple back-projection as shown in Fig.2, and results in a mathematically exact reconstruction of the image.
Specific intensity and the power dP given in Hq. Principle of transcutaneous fluorescent 1ImagIng. Geometry of the theoretical model. Depth dependence of measured PSF spread.
Diamonds and curve are the measurement and the theoretical calculation, respectively. Example of the improvement of transcutaneous fluorescence image using depth-dependent PSF: (a) observed image, (b) depth-dependent PSF, (c) improved image. ® denotes the deconvolution operation. Geometry for PSF as light distribution observed at the scattering medium surface: (a) for fluorescence transcutaneous imaging, (b) for transillumination imaging.
The orange circle denotes the light point sources in both cases. Geometry for PSF as light distribution observed at the scattering medium 1V List of figures surface in reality: (a) for fluorescence transcutaneous imaging, (b) for transillumination imaging. The orange circle denotes the light point sources in both cases. Procedure of proposed technique for transillumination image using light-source PSF.
© denotes the deconvolution operation. Experimental setup for transillumination imaging: d= 4. Comparison of point spread function at depth d= 8.00 mm: (a) observed image with scattering medium, (b) observed image with transparent medium, (c) measured PSF from Ea.5), (đ) light-souree PSF from Ea. Intensity profiles along the centerlines of Figs.
Comparison between theoretical PSF for light source and measured PSF for abSOT©T. LH Họ 58 Fig. Example of simulation process. x denotes the convolution operation.
® denotes the deconvolution OD©TAfIOH. «c1 TH TH ng cư 59 Fig. Result of the scattering suppression technique using light-source PSF at depth cô Cu. Result of the scattering suppression technique using light-source PSF at b0 n5.
Result of the scattering suppression technique using light-source PSF at b0. Result of the scattering suppression technique using light-source PSF at 6l). Result of the scattering suppression technique using light-source PSF at 60006. Comparison between the improved images by using proposed technique and using non-invert technique in terms of the spread (FWHM) of the absorbev.
Original image x of the absorbing object obtained with transparent medium. Result with transillumination image of the absorber at d=2. The intensity profiles show the distribution of light intensity along the dashed lines. Result with transillumination image of the absorber at d=6.
The intensity profiles show the distribution of light intensity along the dashed lines. Result with transillumination image of the absorber at d=10. The intensity profiles show the distribution of light intensity along the dashed lines. 69 List of figures Fig.
Result with transillumination image of the absorber at d=14. The intensity profiles show the distribution of light intensity along the dashed lines. Comparison between the improved images by using proposed technique and using non-invert technique in terms of the spread (FWHM) of the absorbev. Experimental setup for transillumination imaging: d= 4.
Original image x of the absorbing object obtained with transparent medium. Transillumination image at d= 4.00 mm: (a) observed image, (b) PSF from Eq.00 mm, (c) deconvoluted image using Eq.2) with PSF from Eq. Intensity profiles along the dashed lines in Flg. Transillumination image at d= 10.0 mm: (a) observed image, (b) deconvoluted image using Eq.2) with PSF from Eq.46), (c) three-time piece-wise deconvolution with PSF,,,,(@) that obtained by Eqs.
Intensity profiles along the dashed lines in Fig. The PSF calculated from Eq.0 mm and PSF yar (P) calculated from Eq. Experimental setup for transillumination imaging: d= 6. Result with transillumination image of the absorber at d=6.
The intensity profiles show the distribution of light intensity along the dashed lines. -- - c 1112111 TT ng HH nen gvy 80 tig. Side view and top view oŸ phantom model.- + sss + s++sexseeeeeeeesss 80 Fig. Observed and deconvoluted images of absorber: (a) observed image (contrast and sharpness are 0.050), (b) deconvoluted image (contrast and sharpness are 0Ð 5000610 018.