PubMed Health⌕ Search

Biomedical subjects

R Simon

Publications and source records attributed to R Simon.

At least 73 records · Page 4Linked to original sources
PubMed2000

Peres-horodecki separability criterion for continuous variable systems

The Peres-Horodecki criterion of positivity under partial transpose is studied in the context of separability of bipartite continuous variable states. The partial transpose operation admits, in the continuous case, a geometric interpretation as mirror reflection in phase space. This recognition leads to uncertainty principles, stronger than the traditional ones, to be obeyed by all separable states. For all bipartite Gaussian states, the Peres-Horodecki criterion turns out to be a necessary and sufficient condition for separability.

Journal Article↗
PubMed2000

Length and loss of heterozygosity of an intron 1 polymorphic sequence of egfr is related to cytogenetic alterations and epithelial growth factor receptor expression.

Overexpression of epithelial growth factor receptor (EGFR) is correlated with a poor prognosis and reduced steroid receptor expression. Recently, it was demonstrated that the length of a CA repeat in the intron 1 of EGFR correlated with the expression of EGFR in vitro. We investigated 112 cases of cancerous and noncancerous breast tumor samples for loss of heterozygosity (LOH) in intron 1 of the egfr gene and determined the intratumoral EGFR content and genetic alterations by comparative genomic hybridization. Heterozygous tumors with short CA repeats showed elevated EGFR expression in contrast to tumors with longer CA repeats. Tumors with LOH in intron 1 of egfr revealed higher EGFR expression when the longer allele was lost compared with loss of the shorter allele. Additionally, tumors with a loss of the long allele showed more chromosomal alterations, especially a higher frequency of amplifications. We conclude that the CA repeat status in intron 1 of the egfr gene also modulates the intratumoral EGFR content in vivo. Furthermore, LOH at the CA repeat is associated with genetically advanced tumors. Therefore, allele-specific gene expression due to LOH of the CA repeat could be assumed to be an important event in invasive breast cancer development.

Alleles↗
PubMed2000

Estimation of tamoxifen's efficacy for preventing the formation and growth of breast tumors.

BACKGROUND: Several randomized clinical trials have tested the hypothesis that tamoxifen is effective in preventing breast cancer. The largest such trial, the National Surgical Adjuvant Breast and Bowel Project's Breast Cancer Prevention Trial (BCPT), reported a 49% reduction in risk of invasive breast cancer for the tamoxifen group. However, it is unclear whether the effect of tamoxifen in this trial was mainly due to prevention of newly forming tumors or to treatment of occult disease. METHODS: We used various tumor growth models (i.e., exponential and Gompertzian [growth limited by tumor size]) and a computer simulation to approximate the percentage of detected tumors that were initiated after study entry. Maximum likelihood techniques were then used to estimate separately the efficacy of tamoxifen in treating occult disease and in preventing the formation and growth of new tumors. RESULTS: Under the assumptions of most of the growth models, the trial was sufficiently long for substantial numbers of new tumors to form, grow, and be detected during the trial. With the Gompertzian model and all available incidence data from the BCPT, it was estimated that 60% (95% confidence interval [CI] = 40%-80%) fewer new tumors were detected in the tamoxifen group than in the placebo group. Likewise, 35% (95% CI = 6%-63%) fewer occult tumors were detected in the tamoxifen group. With this model, the estimated incidence rate of invasive breast cancer among women in the placebo group of the BCPT was 7.7 (95% CI = 6.6-8.9) per 1000 women per year. Similar results were obtained with three exponential tumor growth models. CONCLUSIONS: These results support the concept that tamoxifen reduced cancer incidence in the BCPT through both treatment of occult disease and prevention of new tumor formation and growth. However, data from prevention trials may never be sufficient to completely distinguish prevention of new tumor formation from treatment of occult disease.

Adult↗
PubMed2000

Pericardiocentesis: differential aspects of a common procedure.

OBJECTIVE: To evaluate the risk and effectiveness of pericardiocentesis in primary and repeat cardiac tamponade. DESIGN: Retrospective analysis. SETTING: Intensive care unit in a medical university hospital. PATIENTS: Sixty-three consecutively admitted patients with cardiac tamponade. INTERVENTIONS: In all patients pericardiocentesis was performed via the subxiphoid pathway after echocardiographic detection of the pericardial effusion. MEASUREMENTS AND RESULTS: There was no adverse event in patients undergoing primary pericardiocentesis, which was sufficient to resolve pericardial effusion in 51 of 63 patients (81%). However, repeat pericardiocentesis necessitated by the recurrence of symptomatic pericardial effusion yielded suboptimal results in 10 of 12 patients (83%). CONCLUSION: Pericardiocentesis is the treatment of choice for primary symptomatic pericardial effusion. In recurrent pericardial effusion surgical approaches appear to be preferable.

Adult↗
PubMed2000

Reading and assessing reports of treatment studies in oncology.

Rapid advances in tumor biology, immunology, genomics, and technology give physicians great hopes for providing patients with better chances in the struggle against cancer. The pace of progress will be slowed, however, if we do not have clear answers regarding which treatments work and do not work. Such answers come from carefully designed, randomized, clinical trials. Such trials require infrastructure, commitment, cooperation, time, and money, and they provide little fame. They are, however, an invaluable contribution of the medical profession to their patients, to their next generation of colleagues, and to future patients. Randomized clinical trials that answer important medical questions definitively should be supported, participated in, and demanded by surgeons and oncologists.

Clinical Trials as Topic↗
PubMed2000

American College of Cardiology/European Society of Cardiology International Study of Angiographic Data Compression Phase I: The effect of lossy data compression on recognition of diagnostic features in digital coronary angiography.

OBJECTIVES: This study intended to determine the effect of varying degrees of lossy Joint Photographic Experts Group (JPEG) compression on detection of coronary angiographic features. BACKGROUND: Compression of digital coronary angiograms facilitates playback of images and decreases cost. There are little data on the effect of compression on the accuracy of coronary angiography. METHODS: At six centers, 71 angiographers each reviewed a set of 100 angiographic sequences. The 100 sequences were divided into four, 25-sequence subsets. Each subset of 25 was displayed either as original images or at one of three compression ratios (CRs) (6:1, 10:1 or 16:1). The effect of lossy compression on the sensitivity and specificity for detection of diagnostic features was determined. The effect of compression on subjective measures of image quality graded by the angiographers was also examined. RESULTS: Lossy compression at a ratio of 16:1 decreased the sensitivity for the detection of diagnostic features (76% vs. 80% p = 0.004). The largest effect was in the detection of calcification (52% vs. 63% at 16:1 compression vs. original images, p < 0.001). Subjective indicators of image quality indicated a reduction in confidence in interpretation at CRs of 10:1 and 16:1. CONCLUSIONS: With increased ratios of lossy compression, a degradation of digital coronary angiograms occurs that results in decreased diagnostic accuracy. The sensitivity for detection of common diagnostic features was decreased, and subjective assessment of image quality was impaired. Caution is warranted in the interpretation of coronary angiograms that have been subjected to lossy JPEG compression beyond a ratio of 6:1.

Adult↗
PubMed2000

American College of Cardiology/European Society of Cardiolgoy International Study of Angiographic Data Compression Phase II: the effects of varying JPEG data compression levels on the quantitative assessment of the degree of stenosis in digital coronary angiography. Joint Photographic Experts Group.

OBJECTIVES: This report describes whether lossy Joint Photographic Experts Group (UPEG) image compression/decompression has an effect on the quantitative assessment of vessel sizes by state-of-the-art quantitative coronary arteriography (QCA). BACKGROUND: The Digital Imaging and Communications in Medicine (DICOM) digital exchange standard for angiocardiography prescribes that images must be stored loss free, thereby limiting JPEG compression to a maximum ratio of 2:1. For practical purposes it would be desirable to increase the compression ratio (CR), which would lead to lossy image compression. METHODS: A series of 48 obstructed coronary segments were compressed/decompressed at CR 1:1 (uncompressed), 6:1, 10:1 and 16:1 and analyzed blindly and in random order using the QCA-CMS analytical software. Similar catheter and vessel start- and end-points were used within each image quartet, respectively. All measurements were repeated after several weeks using newly selected start- and end-points. Three different sub-analyses were carried out: the intra-observer, fixed inter-compression and variable inter-compression analyses, with increasing potential error sources, respectively. RESULTS: The intra-observer analysis showed significant systematic and random errors in the calibration factor at JPEG CR 10:1. The fixed inter-compression analysis demonstrated systematic errors in the calibration factor and recalculated vessel parameter results at CR 16:1 and for the random errors at CR 10:1 and 16:1. The variable inter-compression analysis presented systematic and random errors in the calibration factor and recalculated parameter results at CR 10:1 and 16:1. Any negative effect at CR 6:1 was found only for the calibration factor of the variable inter-compression analysis, which did not show up in the final vessel measurements. CONCLUSIONS: Compression ratios of 10:1 and 16:1 affected the QCA results negatively and therefore should not be used in clinical research studies.

Adult↗
PubMed2000

American College of Cardiology/European Society of Cardiology International Study of Angiographic Data Compression Phase III: measurement of image quality differences at varying levels of data compression.

OBJECTIVES: We sought to investigate up to which level of Joint Photographic Experts Group JPEG) data compression the perceived image quality and the detection of diagnostic features remain equivalent to the quality and detectability found in uncompressed coronary angiograms. BACKGROUND: Digital coronary angiograms represent an enormous amount of data and therefore require costly computerized communication and archiving systems. Earlier studies on the viability of medical image compression were not fully conclusive. METHODS: Twenty-one raters evaluated sets of 91 cine runs. Uncompressed and compressed versions of the images were presented side by side on one monitor, and image quality differences were assessed on a scale featuring six scores. In addition, the raters had to detect pre-defined clinical features. Compression ratios (CR) were 6:1, 10:1 and 16:1. Statistical evaluation was based on descriptive statistics and on the equivalence t-test. RESULTS: At the lowest CR (CR 6:1), there was already a small (15%) increase in assigning the aesthetic quality score indicating "quality difference is barely discernible-the images are equivalent." At CR 10:1 and CR 16:1, close to 10% and 55%, respectively, of the compressed images were rated to be "clearly degraded, but still adequate for clinical use" or worse. Concerning diagnostic features, at CR 10:1 and CR 16:1 the error rate was 9.6% and 13.1%, respectively, compared with 9% for the baseline error rate in uncompressed images. CONCLUSIONS: Compression at CR 6:1 provides equivalence with the original cine runs. If CR 16:1 were used, one would have to tolerate a significant increase in the diagnostic error rate over the baseline error rate. At CR 10:1, intermediate results were obtained.

Adult↗
PubMed2000

Neurophysiological and behavioral indices of time pressure effects on visuomotor task performance.

Using a video game format, this study examined the effects of time pressure (TP) on behavioral and electrocortical indices. The behavioral results were consistent with previous time pressure research in that TP reduced time to perform a task and increases behavioral errors. In addition, electroencephalogram (EEG) measures showed distinctive patterns associated with TP in the theta, mu, and gamma bands along the midline. Site specific changes in the success vs. failure trials were also seen in midline theta at Fz, gamma at Fz, and mu at Cz. Right parietal alpha also differentiated TP and success vs. failure trials. In specific TP (1) increased frontal midline theta activity and (2) increased gamma at midline (frontal, central, and partietal) and in right frontal areas. The results of these findings are discussed in terms of the formation of specific neurocognitive strategies as evidenced by the topographic distribution of task-related modulation of the EEG within certain frequency bands. It is suggested that the effect of TP on visuomotor performance is mediated by adopting either task-relevant or task-irrelevant neurocognitive strategies as evidenced by successful or failed trials, respectively. Whether these strategies are formulated prior to performance or appear spontaneously during task performance remains unclear and is awaiting further experimentation.

Adult↗
PubMed2000

Comparative methodological analysis of erbB-2/HER-2 gene dosage, chromosomal copy number and protein overexpression in breast carcinoma tissues for diagnostic use.

AIMS: This study was performed to test the validity of different methods for determining the status of the erbB-2/HER-2 oncogene in breast cancer tissues for diagnostic use. METHODS AND RESULTS: Forty formalin-fixed, paraffin-embedded breast carcinomas were investigated by fluorescence in situ and comparative genomic hybridization (FISH, CGH) as well as by immunohistochemistry (IHC) using Dako-HercepTest and CB11 antibody (Ventana). Additionally, competitive-differential polymerase chain reaction (cdPCR) was performed on frozen samples to estimate gene dosage alterations of erbB-2/HER-2. Amplification was detected in 12-23% and protein overexpression in 16-68% of the cases, depending on the methodology and/or the reagent used. Perfect concordance (100%) was found between the results of cdPCR and CB11-IHC, and a 97% concordance between FISH and CB11-IHC. The concordance between Dako-HercepTest and CB11-IHC was 78%: seven of eight 2+ carcinomas with the Dako-HercepTest were classified as nonamplified using FISH. CONCLUSIONS: Our results indicate that high-level expression as well as normal erbB-2/HER-2 status of breast carcinomas can be detected reliably both by IHC and gene dosage assessment in paraffin material for diagnostic use. However, borderline results, especially those with 2 + immunopositivity, should be interpreted with caution and increased emphasis should be given to other clinical and prognostic information available.

Adenocarcinoma↗
PubMed2000

American College of Cardiology/ European Society of Cardiology international study of angiographic data compression phase I. The effects of lossy data compression on recognition of diagnostic features in digital coronary angiography.

OBJECTIVES: This study intended to determine the effect of varying degrees of lossy Joint Photographic Experts Group (JPEG) compression on detection of coronary angiographic features. Background Compression of digital coronary angiograms facilitates playback of images and decreases cost. There are little data on the effect of compression on the accuracy of coronary angiography. METHODS: At six centers, 71 angiographers each reviewed a set of 100 angiographic sequences. The 100 sequences were divided into four, 25-sequence subsets. Each subset of 25 was displayed either as original images or at one of three compression ratios (CRs) (6:1, 10:1 or 16:1). The effect of lossy compression on the sensitivity and specificity for detection of diagnostic features was determined. The effect of compression on subjective measures of image quality graded by the angiographers was also examined. RESULTS: Lossy compression at a ratio of 16:1 decreased the sensitivity for the detection of diagnostic features (76% vs. 80%P=0.004). The largest effect was in the detection of calcification (52% vs. 63% at 16:1 compression vs. original images, P<0.001). Subjective indicators of image quality indicated a reduction in confidence in interpretation at CRs of 10:1 and 16:1. CONCLUSIONS: With increased ratios of lossy compression, a degradation of digital coronary angiograms occurs that results in decreased diagnostic accuracy. The sensitivity for detection of common diagnostic features was decreased, and subjective assessment of image quality was impaired. Caution is warranted in the interpretation of coronary angiograms that have been subjected to lossy JPEG compression beyond a ratio of 6:1.

Adult↗
PubMed2000

American College of Cardiology/ European Society of Cardiology international study of angiographic data compression phase II. The effects of varying JPEG data compression levels on the quantitative assessment of the degree of stenosis in digital coronary angiography.

OBJECTIVES: This report describes whether lossy Joint Photographic Experts Group (JPEG) image compression/decompression has an effect on the quantitative assessment of vessel sizes by state-of-the-art quantitative coronary arteriography (QCA). BACKGROUND: The Digital Imaging and Communications in Medicine (DICOM) digital exchange standard for angiocardiography prescribes that images must be stored loss free, thereby limiting JPEG compression to a maximum ratio of 2:1. For practical purposes it would be desirable to increase the compression ratio (CR), which would lead to lossy image compression. METHODS: A series of 48 obstructed coronary segments were compressed/decompressed at CR 1:1 (uncompressed), 6:1, 10:1 and 16:1 and analyzed blindly and in random order using the QCA-CMS analytical software. Similar catheter and vessel start- and end-points were used within each image quartet, respectively. All measurements were repeated after several weeks using newly selected start- and end-points. Three different sub-analyses were carried out: the intra-observer, fixed inter-compression and variable inter-compression analyses, with increasing potential error sources, respectively. RESULTS: The intra-observer analysis showed significant systematic and random errors in the calibration factor at JPEG CR 10:1. The fixed inter-compression analysis demonstrated systematic errors in the calibration factor and recalculated vessel parameter results at CR 16:1 and for the random errors at CR 10:1 and 16:1. The variable inter-compression analysis presented systematic and random errors in the calibration factor and recalculated parameter results at CR 10:1 and 16:1. Any negative effect at CR 6:1 was found only for the calibration factor of the variable inter-compression analysis, which did not show up in the final vessel measurements. CONCLUSIONS: Compression ratios of 10:1 and 16:1 affected the QCA results negatively and therefore should not be used in clinical research studies.

Cardiology↗
PubMed2000

American College of Cardiology/ European Society of Cardiology international study of angiographic data compression phase III. Measurement Of image quality differences at varying levels of data compression.

OBJECTIVES: We sought to investigate up to which level of Joint Photographic Experts Group (JPEG) data compression the perceived image quality and the detection of diagnostic features remain equivalent to the quality and detectability found in uncompressed coronary angiograms. BACKGROUND: Digital coronary angiograms represent an enormous amount of data and therefore require costly computerized communication and archiving systems. Earlier studies on the viability of medical image compression were not fully conclusive. METHODS: Twenty-one raters evaluated sets of 91 cine runs. Uncompressed and compressed versions of the images were presented side by side on one monitor, and image quality differences were assessed on a scale featuring six scores. In addition, the raters had to detect pre-defined clinical features. Compression ratios (CR) were 6:1, 10:1 and 16:1. Statistical evaluation was based on descriptive statistics and on the equivalence t -test. Results At the lowest CR (CR 6:1), there was already a small (15%) increase in assigning the aesthetic quality score indicating "quality difference is barely discernible-the images are equivalent.' At CR 10:1 and CR 16:1, close to 10% and 55%, respectively, of the compressed images were rated to be "clearly degraded, but still adequate for clinical use' or worse. Concerning diagnostic features, at CR 10:1 and CR 16:1 the error rate was 9.6% and 13.1%, respectively, compared with 9% for the baseline error rate in uncompressed images. CONCLUSIONS: Compression at CR 6:1 provides equivalence with the original cine runs. If CR 16:1 were used, one would have to tolerate a significant increase in the diagnostic error rate over the baseline error rate. At CR 10:1, intermediate results were obtained.

Adult↗
PubMed2000

Total occlusion trial with angioplasty by using laser guidewire. The TOTAL trial.

AIMS: A randomized trial was performed to assess the safety and efficacy of a laser guidewire, in the treatment of chronic coronary occlusions. METHODS AND RESULTS: In 18 European centres, 303 patients with a chronic coronary occlusion were randomized to treatment with either the laser guidewire (n=144) or conventional guidewires (mechanical guidewire, n=159). The primary end-point of the study was treatment success, defined as reaching the true lumen distal to the occlusion by the allocated wire within 30 min of fluoroscopic time: laser guidewire vs mechanical guidewire; 52.8% (n=76) vs 47.2% (n=75), P=0.33. Serious adverse events following the initial guidewire attempt were 0% (laser guidewire) and 0.6% (mechanical guidewire), respectively. Angioplasty (performed following successful guidewire crossing) was successful in 179 patients (91%, laser guidewire n=79, mechanical guidewire n=100), followed by stent implantation in 149 (79%). At the 6-month angiographic follow-up, the difference in binary restenosis rate (laser guidewire vs mechanical guidewire; 45.5% vs 38.3 %, P=0.72) or reocclusion rate (25.8% vs 16.1%, P=0.15) did not reach statistical significance. At 1, 6 and 12 months, angina and event-free survival were 69%, 35% and 24% (laser guidewire) vs 74%, 40% and 31% (mechanical guidewire). CONCLUSION: Although laser guidewire technology was safe, the increase in crossing success did not reach statistical significance.

Aged↗
PubMed2000

Comparative genomic hybridization in pineal germ cell tumors.

Fifteen primary pineal germ cell tumors (8 germinomas, 4 mixed teratomas-germinomas, 2 immature teratomas, and 1 yolk sac tumor) and 2 recurrences of the yolk sac tumor were studied by comparative genomic hybridization (CGH). An average of 1.8 chromosomal changes per germinoma (0.5 gains vs 1.3 losses), 5.5 per mixed teratoma-germinoma (3.0 gains vs 2.5 losses), 3.5 per immature teratoma (2.0 gains vs 1.5 losses), and 2.0 in the yolk sac tumor (2 gains vs 0 losses) were found; the first recurrence showed 7 (4 gains vs 3 losses), the second 13 imbalances (8 gains vs 5 losses). The most frequent imbalances were gains on 12p (40%), 8q (27%), and 1q (20%) as well as losses on 13q (47%), 18q (33%), 9q and 11q (20% each). Among germinomas, the most common chromosomal changes were -13q and -18q (38% each), in mixed teratomas-germinomas +8q (100%), +12p (75%), -13q (75%) and -9q (50%). Seven high-level gains were identified: 5 in mixed teratomas-germinomas (+8q: 3 cases, + 12p: 2 cases), 1 each in a germinoma (+2p) and an immature teratoma (+12p). Minimal common regions of over- and underrepresentation were found on +8q11.22-21.1, +12p11.1-12.1, -9q32-qter, -11q23.2-qter, -13q32-qter and -18q22-qter. Our findings suggest, that imbalances in cerebral germ cell tumors affect the same chromosomes as among their extracerebral counterparts, albeit in a considerably lower frequency among cerebral germinomas where +12p does not seem to play a major role.

Adolescent↗