PubMed Health⌕ Search

Biomedical subjects

J Papaioannou

Publications and source records attributed to J Papaioannou.

At least 19 recordsLinked to original sources
PubMed2001

Dependence of computer classification of clustered microcalcifications on the correct detection of microcalcifications.

Our purpose was to study the dependence of computer performance in classifying clustered microcalcifications as malignant or benign on the correct detection of microcalcifications. Specifically, we studied the effects of computer-detected true-positive microcalcifications and computer-detected false-positive microcalcifications in true microcalcification clusters. Using a database of 100 mammograms, we compared computer classification performance obtained from computer-detected microcalcifications to (1) computer classification performance obtained from manually identified microcalcifications, and (2) radiologists' performance. When an artificial neural network (ANN) was trained with manually identified microcalcifications, computer classification performance was comparable to or better than radiologists' performance as the number of computer-detected true-positive microcalcifications decreased to 40% and as the number of computer-detected false-positive microcalcifications increased to 50%. Further loss in computer-detected true-positive microcalcifications degraded classification performance substantially. Moreover, training the ANN with computer-detected microcalcifications also degraded computer classification performance. These results show that computer performance in classifying clustered microcalcifications as malignant or benign is insensitive to moderate decreases in computer-detected true-positive microcalcifications and moderate increases in computer-detected false-positive microcalcifications.

Breast Neoplasms↗
PubMed1998

Analysis of methods for reducing false positives in the automated detection of clustered microcalcifications in mammograms.

Clustered microcalcifications are often the first sign of breast cancer in a mammogram. Nevertheless, all clustered microcalcifications are not found by an individual radiologist reading a mammogram. The use of a second reader may find those clusters of microcalcifications not found by the first reader, thereby improving the sensitivity of detecting clustered microcalcifications. Our laboratory has developed a computerized scheme for the detection of clustered microcalcifications, which can act like a second reader, that is undergoing clinical evaluation. This paper concerns the feature analysis stage of the computer scheme, which is designed to remove some of the false-computer detections. We have examined three methods of feature analysis, namely, rule based (the method currently used), an artificial neural network (ANN), and a combined method. In an independent database of 50 images, at a sensitivity of 83%, the average number of false positive (FP) detections per image was: 1.9 for rule-based, 1.6 for ANN, and 0.8 for the combined method. We demonstrate that the combined method performs best because each of the two stages eliminates different types of false positives.

Breast Neoplasms↗
PubMed1995

Image feature analysis and computer-aided diagnosis in mammography: reduction of false-positive clustered microcalcifications using local edge-gradient analysis.

To improve the performance of a computerized scheme for detection of clustered microcalcifications in digitized mammograms, causes of detected false-positive microcalcification signals were analyzed. The false positives were grouped into four categories, namely, microcalcification like noise patterns, artifacts, linear patterns, and others. In an edge-gradient analysis, local edge-gradient values at signal-perimeter pixels of detected microcalcification signals were determined to eliminate false positives that look like subtle microcalcifications or are due to artifacts. In a linear-pattern analysis, the degree of linearity for linear patterns was determined from local gradient values from a set of linear templates oriented in 16 different directions. Threshold values for the edge-gradient analysis and the linear-pattern analysis were determined using a training database of 39 mammograms. It was possible to eliminate 59% and 25%, respectively, of 91 detected false-positive clusters with loss of only 3% of true-positive clusters. The combination of the two methods further improved the scheme in eliminating a total of 73% of the false-positive clusters with loss of 3% of true-positive clusters. Using these thresholds, the two methods were evaluated on another database of 50 mammograms. 62%, 31%, and 80% of the false-positive clusters were eliminated with loss of 3% of true-positive clusters or less, in the edge-gradient analysis, the linear-pattern analysis, and the combination of the two methods, respectively. The edge-gradient analysis and the linear-pattern analysis can reduce the false-positive detection rate, while maintaining a high level of the sensitivity.

Artifacts↗
PubMed1995

Computerized detection of clustered microcalcifications: evaluation of performance on mammograms from multiple centers.

To investigate the performance of a computerized method for the automated detection of clustered microcalcifications in digitized mammograms from a variety of screening centers, the authors invited 118 radiologists to bring up to five mammograms to their scientific exhibit at the 1993 meeting of the Radiological Society of North America (RSNA). Forty-three mammograms from 14 sites were brought to the exhibit, where they were digitized and analyzed. Results of the analysis on the RSNA cases were compared with those obtained on a standard database of 39 mammograms collected from two centers. The performance of the detection algorithm on the RSNA images was lower than that achieved on the standard database. This lower performance was due in part to the higher fraction of very subtle clustered microcalcifications in the RSNA cases, as well as the apparent dependence of the algorithm on image characteristics (eg, contrast and noise), which varied from center to center. The authors conclude that the algorithm is robust and accurate enough to undergo clinical testing. When it is implemented clinically, the computerized scheme must be customized to the image characteristics at each specific screening center to obtain optimal performance.

Breast Diseases↗
PubMed1986

Expression of class I MHC proteins on RIN-m5F cells is increased by interferon-gamma and lymphokine-conditioned medium.

To examine whether products of the immune system interact with the pancreatic beta-cell, rat insulinoma cells (RIN-m5F line) were cultured in the presence of conditioned medium from concanavalin A-activated mouse spleen cells (CAS medium). Indirect immunofluorescence and flow cytometry revealed that after culture in CAS medium, RIN-m5F cells had an 8- to 10-fold increase in class I major histocompatibility complex (MHC) proteins, whereas class II MHC proteins remained undetectable, and the level of insulin and/or insulin-like growth factor 1 receptors was unchanged. The stimulation of class I MHC expression on RIN-m5F cells by CAS medium could be mimicked by recombinant interferon-gamma. Analysis of 125I-surface-labeled cells by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography revealed that in the presence of CAS medium, there was a major increase in the expression of proteins of 48,000, 32,000, and 12,000 Mr and a minor increase in proteins of 17,000 and 9,000 Mr. Precipitation with monoclonal antibody identified the 48,000- and 12,000-Mr proteins as the class I MHC protein and beta 2-microglobulin, respectively. The ability of lymphokine-conditioned medium to increase the expression of RIN-m5F cell surface proteins, including the class I MHC proteins, provides a potential mechanism for enhancing the immune-mediated destruction of the beta-cell.

Adenoma, Islet Cell↗
PubMed1985

Flow-cytometric determination of fluorescence ratios between differently stained particles is dependent on excitation intensity.

By use of a flow cytometer, the fluorescence of cells stained with hematoporphyrin derivative and the fluorescence of plastic beads stained with different dyes were analysed as a function of the intensity of the exciting laser light. The ratios of the fluorescence values of stained and unstained cells as well as of stained cells and beads were sensitively dependent on excitation intensities. As a consequence of this finding, the normalization of cellular fluorescence by use of reference particles needs to be made on a well-defined and reproduced intensity of the exciting laser light.

Animals↗
PubMed1978

[Surgical treatment of associated coronary disease and heart valve disease].

25 patients underwent combined surgery for coronary artery and valvular heart disease. Although patients suffering from associated coronary artery and valvular lesions represent a high operative risk group, the combined surgical procedure is clearly justified by the functional improvement of the patients. Selective coronaro-angiography should be carried out in the assessment of patients over 40 years of age with valvular disease, since not all patients present angina in spite of diseased coronary arteries. Three hospital deaths (13.5%) indicate the gravity of the procedure, but the absence of intra- or postoperative myocardial infarction and the comparatively rapid recovery of the patients with relatively few complications are very encouraging.

Adult↗
PubMed1975

[Proceedings: Results of the surgical treatment of valvulopathies and ischemic heart disease in patients older than 65 years].

53 patients aged from 65 to 76 years underwent surgery for valvulopathies (23 patients), atherosclerotic heart disease (24 patients) or both diseases combined (6 patients). All these cases were in NYHA fonctional classes III and IV except for one patient in class II. Hospital mortality after surgical treatment of these cardiopathies was 3.8% (2 deaths). The late mortality of 19% (10 deaths), though high, was of non-cardiac origin in 7 of these patients. The clinical and hemodynamic findings in the two patients who died in the postoperative period were compared with those in the others. These two patients were more severely ill and had a greater degree of cardiomegaly than the average patient in the surviving group. The satisfactory clinical improvement in these elderly cardiac patients suggests that surgery can be recommended at least up to 75 years of age if there are no obvious contraindications. Life expectancy of 13-16 years for patients aged 65 and 8-9 years for patients aged 75 is a further reason for advocating surgical intervention.

Aged↗
PubMed1975

[Surgery of aortic valvulopathies].

75 patients were operated for isolated aortic congenital or acquired valvulopathies (46 men, 25 women and 4 children). 8 patients were reoperated because of functional defects of the artificial valve or paravalvular dehiscence. 3 children from 3 to 10 years of age underwent aortic valvular commissurotomy. The other patients had aortic valve replacement by an artificial valve. Two types of valves were used. In the beginning, we employed the Starr-Edwards valves, models 1200, 2300, 2310 and 2320. Since July 1971, we are using the Björk-Shiley valve. Less pressure gradient across the valve and less hemolysis with Björk-Shiley valve are two important factors in favoring its use. Our hospital mortality has been 5.3% and late mortality also 5.3%. Clinical improvement is observed among 80% of patients in follow-up controls.

Adolescent↗
PubMed1974

Does the vestibular apparatus play a role in the development of the visual system?

1. The receptive field properties of visual cortical neurones were investigated in kittens that had been subjected to either unilateral or bilateral labyrinthectomy shortly after birth.2. Two kittens were reared in a normal visual environment. Another two were reared in the dark with recurrent exposures to vertically oriented black and white stripes, which in normal kittens is known to bias the distribution of receptive field orientations.3. For both normally reared and stripe-reared labyrinthectomized kittens, no differences were detected in cell types, preferred orientations, binocularity, columnar organization, or any other neuronal properties, compared with similarly reared intact kittens.4. The failure to detect deficits in visual development after labyrinthectomy is discussed in relation to other reports of vestibular influences on the visual system of the adult cat.

Journal Article↗