E. Kahn

Handling of Dynamic Sequences in Nuclear Medicine

Nuclear Medicine is one of the first domains in which the analysis of image sequences was introduced. The development of this analysis was achieved parallel to the one of the computer systems linked to the scintillation cameras. The number of works that were performed in the research laboratories and have received an application in clinical routine is however limited. The authors indicate what could be the flow chart of the processing of dynamic sequences in scintigraphy and the kind of material that would be necessary to implement it. The possibilities of using the factor and compartmental analyses in clinical routine are particularly emphasized. The authors indicate why the factors and their associated images obtained by means of the factor analysis can have a physiological meaning.

A fractal approach to the segmentation of microcalcifications in digital mammograms

This paper presents a computerized method for the automated segmentation of individual microcalcifications in a region of interest (ROI) known to contain a cluster in digital mammograms. Mammographic parenchyma caj be accurately modeled with the fractal approach, but not areas with microcalcifications. The digitized image is divided into 16 x 16-pixel overlapping windows and those accurately modeled by the fractal model are eliminated. The next steps include local thresholding of the ROIs using an iterative method, the elimination of some of the artifacts and identification of the clustered microcalcifications using a clustering algorithm. The evaluation was performed on 81 simulated clusters superimposed on normal mammographic backgrounds and on a representative database of 408 real mammograms. Microcalcification locations were identified by two radiologists independently. These locations were compared to those found by the computer algorithm. An average of 59% of the simulated microcalcifications and 69% of the microcalcifications common to both radiologists were detected. The algorithm described provides a fully automated method for the segmentation of individual microcalcifications in an area of the mammogram known to contain a cluster.

Lung scintigraphy clustering by texture analysis.

The efficiency of texture analysis parameters, describing the organization of grey level variations of an image, was studied for lung scintigraphic data classification. Twenty one patients received a99mTc-MAA perfusion scan and81mKr and and127 Xe ventilation scans. Scans were scaled to 64 grey levels and 100 k events for inter subject comparison. The texture index was the average of the absolute difference between a pixel and its neighbors. Energy, entropy, correlation, local homogeneity and inertia were computed using co-occurence matrices. A principal component analysis was carried out on each parameter for each type of scan and the first principal components were selected as clustering indices. Validation was achieved by simulating 2 series of 20 increasingly heterogeneous perfusion and ventilation scans. For most of the texture parameters, one principal component could summarize the patients data since it corresponded to the relative variances of 67%-88% for perfusion scans, 53%–99% for81mKr scans and 38%–97% for127Xe scans. The simulated series demonstrated a linear relationship between the heterogeneity and the first principal component for texture index, energy, entropy and inertia. This was not the case for correlation and local homogeneity. We conclude that heterogeneity of lung scans may be quantified by texture analysis. The texture index is the easiest to compute and provides the most efficient results for clinical purpose.

Detection and display of defects in medical scintigraphic images

Abstract To achieve the evaluation of the lesion detectability of a program implemented by us on a minicomputer system to indicate possible defects on liver scans, we simulated a set of geometrical phantoms with different patterns of cold lesions to obtain LROC curves in different cases. Then, to check its clinical value, the program was applied to 44 liver scintigrams of patients among which 7 occurred to be pathological. These liver scintigrams had been evaluated by 6 clinicians so that a comparison between the program and the clinicians could be performedd on the basis of the corresponding LROC curves. Moreover, once an abnormality had been detected by the program, the abnormality was processed in order to perform a psychovisual evaluation of the image more easily: an adapted local 2-level display of the possible defect was superimposed on the scan to enhance it and to facilitate diagnosis.

Nuclear configuration of bladder cancer associated to bilharziosis: Preliminary study by confocal microscopy

Confocal laser scanning microscopy (CLSM) offers several advantages over conventional fluorescence microscopy for the in ~im hx:alization of flL~orescently labeled targets and probes in cells and tissues : (i) rejection of fluorescence signals from out-of-focus planes and from neighboring suructures. Oi) improvement of both lateral and axial resolutions. (iii) electronic adjustement of contrast brightness and magnification, (iv) sinmltaneous visualization of the specimen by using optical phenomena based on incident, scattered. emitted and transmitted light, (v) simultaneous use of different fluorescent probes and types of detectors, (vi) acquisition of serial optical sections for generation of 3-D ~constrnctions without time consuming deconvolution procedures. Qualitative analyses of the can be effectively performed by visual {nspection of reconstructed images using stereo projectioo. For quantitative evaluation of 3-D dismbudons, contour extraction, surface and volume reconstructions can be undertaken. CLSM has proved to be a powerful technique for muhiparameter and tridintensional in .~itu analyses on intact cells, tissues and whole embryos. Several levels of the structural and functional organization of the chromatin in the cell nucleus were investigated : (i) the conformational state of the DNA, (it) the distribution of euand heterochromatic regions, (iii) the localization of DNA replication sites, (iv) the redistribution of nuclear and nucleolar proteins during the cell cycle. (v) the condensation aod %patti arrangement of the chromosomes. (vii the localization of parucular DNA SalUences and of individual genes. Probes used in these studies include : (i) DNA fluorescent dyes, (it) chemical reagents revealed by immunofluorescence, (iii) antibodies recognizing nuclear proteins. DNA conformation, and modified DNA bases. (iv) markers of the cell cycle and proliferation. (v) DNA probes for non-isotopic in sita hybridization. These probes were used either individually or in various combinations with each other, in order to establish possible correlations between the structural state of the chmmatin and its funcuonal state in cycling and in differentiated cells. NUCLEAR CONFIGURATION OF BLADDER CANCER ASSOCIATED TO BILHARZIOSIS : PRELIMINARY STUDY BY CONFOCAL MICROSCOPY. NASR Safaa*, MOUKHTAR Nadia**, MANSOUR Abbas**. OMRI DE LANGEN FrtM~rique***, KAHN Edmond***. * Nemrock EM Center of EEC NCRRT Facully o f Medicine Cairo Egypt. ** National Cancer institute Cairo Egypt. *** INS~RM ;.166institut Gustave-Rma~.94805 ~7LLEJ&aF Cedex France.