Volume 3 Supplement 1
Automated region of interest retrieval and classification using spectral analysis
© Oger et al; licensee BioMed Central Ltd. 2008
Published: 15 July 2008
Efficient use of whole slide imaging in pathology needs automated region of interest (ROI) retrieval and classification, through the use of image analysis and data sorting tools. One possible method for data sorting uses Spectral Analysis for Dimensionality Reduction. We present some interesting results in the field of histopathology and cytohematology.
In histopathology, we developed a Computer-Aided Diagnosis system applied to low-resolution images representing the totality of histological breast tumour sections. The images can be digitized directly at low resolution or be obtained from sub-sampled high-resolution virtual slides. Spectral Analysis is used (1) for image segmentation (stroma, tumour epithelium), by determining a «distance» between all the images of the database, (2) for choosing representative images and characteristic patterns of each histological type in order to index them, and (3) for visualizing images or features similar to a sample provided by the pathologist.
In cytohematology, we studied a blood smear virtual slide acquired through high resolution oil scanning and Spectral Analysis is used to sort selected nucleated blood cell classes so that the pathologist may easily focus on specific classes whose morphology could then be studied more carefully or which can be analyzed through complementary instruments, like Multispectral Imaging or Raman MicroSpectroscopy.
Efficient use of whole slide imaging (WSI) in Pathology needs an automated region of interest (ROI), retrieval and classification; this can be achieved through the use of image segmentation and data sorting tools. The present paper aims at illustrating, through two examples, the power of spectral analysis, which can be used alone or in addition to image segmentation for data reduction, feature classification as well as image visualisation.
Materials and methods
The first application concerns 73 WSI of HES stained histological sections of breast tumours recorded at a resolution of 6.3 μ m/pixel. The second one concerns a WSI of MG stained blood smear recorded at a resolution of 0.17 μ m/pixel using an Aperio slide scanner.
A minimal segmentation was performed to isolate breast tumour tissue or to eliminate erythrocytes from blood smear.
Principle of spectral analysis
is the degree of node x i .
the quantity p(x i , x j ) ≥ 0 can be interpreted as the probability of random walker to jump from x i to x j in single time step.
From spectral theory and harmonic analysis we know that the eigenfunctions can be interpreted as a generalization of the Fourier harmonics on the manifold defined by the data points. In our problem, smaller eigenvalues correspond to higher frequency eigenfunctions, and larger eigenvalues correspond to lowers ones.
Spectral Analysis is a promising approach for computer aided diagnosis of cancers (automated global analysis of histological tumour sections) as well as for automated sorting of isolated cells. The resulting concentration of objects of interest allows the pathologist to focus on specific regions whose morphology can be further studied more carefully or analyzed through complementary instruments, like Multispectral Imaging or Raman spectroscopy.
The authors gratefully acknowledge Dr Paulette Herlin, Dr Benoît Plancoulaine, Dr Jacques Chasle, Dr Georges Flandrin, the Regional Council of Lower Normandy, the "Comité départemental du Calvados de la Ligue de Lutte Contre le Cancer" and the General Council of "Hauts-de-Seine".
This article has been published as part of Diagnostic Pathology Volume 3 Supplement 1, 2008: New trends in digital pathology: Proceedings of the 9th European Congress on Telepathology and 3rd International Congress on Virtual Microscopy. The full contents of the supplement are available online at http://www.diagnosticpathology.org/supplements/3/S1
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