trans-rectal near-infrared optical tomography reconstruction of a regressing experimental tumor in a...
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Trans-rectal near-infrared optical tomography reconstruction of a regressing experimental
tumor in a canine prostate by using the prostate shape profile synthesized from sparse 2-dimentional trans-rectal ultrasound images
Dhanashree Palande, Daqing PiaoSchool of Electrical and Computer Engineering,
Oklahoma State University, Stillwater, OK 74078, USA
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Outline
Objective• Methods• Results• Conclusion and future work
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Objective• Near infrared(NIR) optical imaging:
– well suited for non-invasive quantification of hemoglobin oxygen saturation(StO2)
– provides unique information regarding optical properties
• Limitation of NIR: – low spatial resolution due to high scattering in
tissue• Solution:
– compensate optical imaging with spatial prior information extracted from high resolution trans-rectal ultrasound (TRUS) images to improve the reconstruction outcome of trans-rectal DOT
– obtain a 3D prostate profile from 2D TRUS images using segmentation which is used as a structural spatial prior in optical tomography reconstruction
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Outline
• Objective Methods• Results• Conclusion and future work
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NIR Optical Tomography(DOT)
• Non-invasive imaging technique: aims to reconstruct images of tissue function and physiology
• Biological tissue is highly scattering at NIR wavelengths (650-900 nm)
• Also known as diffuse optical tomography(DOT)• NIR light is applied through optical fibers
positioned to surface of the tissue• Emergent light is measured at other locations on
the same tissue surface • NIR optical tomography along with reconstruction
algorithm, produces images of tissue physiology for detection and characterization of malignancy
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HbT and StO2 measurement
• In the range 700-900nm, absorption of water is much lower than that of oxygenated hemoglobin and deoxygenated hemoglobin
• Multi-wavelength data:– Rendered extracting oxygen saturation and hemoglobin concentration.– 705 nm, 785 nm, 808 nm
• Absorption coefficients recovered at 3 specific bands are:
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HbT and StO2 measurement
• They are used to calculate HbO and Hb as
Where, was matrix of molar extinction coefficients
• Total hemoglobin: HbT= HbO+Hb (in milliMole)
• Oxygen saturation: StO2=HbO/HbT x 100 (in %)
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NIR Reconstruction Geometry
• Outer rectangular mesh: – equivalent to tissue surrounding the prostate– Required to match NIR reconstruction geometry
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The Forward Model• The technique to determine what a given sensor
would measure in given environment by using theoretical equations for sensor response
• Diffusion approximation in frequency domain
Where : absorption coefficient: reduced scattering coefficient : isotropic source term : photon fluence rate at position r and modulation frequency : diffusion coefficient : speed of light in medium
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The Inverse Model• Using the results of actual observations to infer
the values of the parameters characterizing the system under investigation.
• Goal: recovery of optical properties at each spatial element
• Tikhonov minimization: : measured fluence at tissue surface : calculated data using forward solver
Where, NM: number of measurements from imaging device
NN: number of spatial elements : regularization parameter : initial estimate of optical properties
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The Inverse Model• The minimization with respect to μ in equation
: Jacobian matrix, JUsing linear approximation and solving it as iterative scheme,
Where, : update of optical properties: data-model misfit at current iteration I I: identity matrix
Slight modification gives,
Where, and 11
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The Inverse Model
• NIRFAST is used for inverse problem solving
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TRUS Images of a Canine Prostate• A canine prostate was used for study
• Transmissible Venereal Tumor(TVT) cells was injected in right lobe of a prostate
• Dog was monitored over the
63-days period, at weekly intervals
• TRUS images were taken at:– Right edge plane– Right middle plane– Middle sagittal plane– Left middle plane– Left edge plane 13
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TRUS Images of a Canine Prostate
Axial view Sagittal view
rectumrectum
Left lobeRight lobe
Caudal side
Cranial side
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TRUS Images of a Canine Prostate
Axial view Sagittal view
rectumrectum
Left lobeRight lobe
Caudal side
Cranial side
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TRUS Image Segmentation
• TRUS image segmentation is challenging due to– Complexity in contrast – Image artifacts– Morphological features– Variation in prostate shape and size
• Manual contour tracking– Interactive program takes input
from user– Sagittal images segmented manually– Used as reference for 3D profile
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Approximating Axial Plane
Positions
• We have set of sparsely acquired axial images• We use 3 images at cranial side, middle and
caudal side of the prostate• A program is written
to find approximate positions of these axialplanes
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3D Profiling of a Prostate
• Interpolation– Spline type of interpolation for smooth profile
along the curve– Using the points on axial contours– New data points are interpolated depending on
required mesh density
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Mesh Generation
• Generation of a 3D mesh prostate profile using Delaunay triangulation– Input: interpolated data points from 3D profile– Output: elements of all the tetrahedrons
• This mesh is now used as a spatial prior for NIR image reconstruction
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Prostate Mesh within Rectangular
Mesh
• Mesh used for reconstruction
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Outline
• Objective• Methods Results• Conclusion and future work
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Manually Segmented Images
For axial images
For sagittal images
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3D Prostate Profile
3D profile of prostate
3D mesh profile of a prostate
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Rectangular Mesh
With spatial prior Without spatial prior
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Reconstruction: Right LobeBaseline
With spatial prior Without spatial prior
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60 mm 60 mm
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mm
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mm
Ultrasound image
HbT
StO2
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Reconstruction: Right LobeDay 49
With spatial prior Without spatial prior
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90
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90
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60 mm 60 mm
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mm
40
mm
Ultrasound image
HbT
StO2
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Reconstruction: Right LobeDay 56
With spatial prior without spatial prior
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90
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60 mm 60 mm
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mm
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Ultrasound image
HbT
StO2
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Right Lobe
40
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Right Lobe
(weeks) 7 8 9 7 8 9 (weeks)
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Reconstruction: Left Lobe
Day 49With spatial prior without spatial prior
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90
40
90
40
60 mm60 mm
40
mm
40
mmUltrasound image
HbT
StO2
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Left Lobe
Day 63With spatial prior without spatial prior
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90
40
90
40
60 mm60 mm
40
mm
40
mm
Ultrasound image
HbT
StO2
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Left Lobe
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90
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90
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Outline
• Objective• Methods• Results Conclusion and future work
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Conclusion and future work
- Contribution of this work• This work explores combination of structural and
functional imaging for the study of prostate cancer• 3D prostate profile was generated from sparse 2D axial
TRUS images of a canine prostate• A prostate mesh developed was used a spatial prior to
NIR optical tomography for image reconstruction• Reconstructed images with and without prior were
compared qualitatively• This approach helps to interpret results for good
understanding of position of tumor lesion developed in prostate.
• To our knowledge, this is the first attempt to use TRUS guided structural spatial prior for image reconstruction of a prostate using NIR optical tomography
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Conclusion and future work
-Future directions• Extending this study to other animals and
eventually to human prostates• Applying spectral prior information along with
spatial prior• To make this system work real-time, so as to be
used during clinical exams
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Thank youQuestions/suggestions
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