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PubMed1991

ROC curves and the binormal assumption.

Previous articles in this series have described how receiver operating characteristic (ROC) graphs provide comprehensive graphic representations of the diagnostic performance of non-binary tests and have explained how one constructs "trapezoidal" ROC graphs in which discrete cutoff points are plotted and connected with line segments. In this article, we describe a set of mathematical assumptions that permit the generation of a continuous, smooth ROC curve for a given diagnostic test. These assumptions permit us to characterize a test's performance using a small number of parameters and also to explore properties of diagnostic tests. In this article, we describe a set of mathematical assumptions that can be used to link receiver operating characteristic (ROC) curves to the underlying distribution of values of the diagnostic variable being measured. We will illustrate these assumptions using a diagnostic test that distinguishes alcohol abusers from normal consumers of alcohol and abstainers.

Alcoholism↗
PubMed2006

A quadratic model for combining quantitative diagnostic assessments from radiologist and computer in computer-aided diagnosis.

RATIONALE AND OBJECTIVES: Some computer-aided diagnosis (CAD) methods produce a quantitative diagnostic assessment (eg, likelihood of malignancy) based on computer image analysis that a radiologist who uses the computer aid must combine with his or her own assessment. Observer studies show that although CAD helps radiologists improve diagnostic performance, ad hoc use of computer aid can produce performance inferior to that of computer alone, indicating that radiologists are unable to incorporate computer assessment optimally into their final assessment. We describe a mathematical model for combining two correlated diagnostic assessments that may provide a basis for merging radiologists' ratings with computer assessments in a way that yields greater diagnostic accuracy than ad hoc merging by radiologists. MATERIALS AND METHODS: We calculate a likelihood ratio from the bivariate binormal model that describes joint probability density functions of latent decision variables of two correlated diagnostic assessments. To the extent that the bivariate binormal model is valid and that the model's parameters can be estimated reliably, results obtained in this way will be optimal because the likelihood ratio is the decision variable used by the ideal observer in any two-group classification task. We evaluated this method on two observer study datasets and in Monte Carlo simulations. RESULTS: This method produced better performance than achieved by radiologists when they incorporated computer assessment in an ad hoc way. Simulations show that with a large number of cases, this method can produce results indistinguishable from the ideal observer performance. CONCLUSIONS: This method can potentially help radiologists use quantitative computed diagnostic assessments optimally, thereby surpassing the computer in accuracy.

Analysis of Variance↗
PubMed2000

Preliminary evaluation of LATEX/T. b. gambiense and alternative versions of CATT/T. b. gambiense for the serodiagnosis of human african trypanosomiasis of a population at risk in Côte d'Ivoire: considerations for mass-screening.

A study was conducted to compare classical card agglutination test for trypanosomiasis (CATT)/T. b. gambiense with CATT-EDTA and LATEX/T. b. gambiense as alternative field tests for serodiagnosis of Human African Trypanosomiasis. The tests were performed on freshly collected blood in an endemic and a low prevalence area in Côte d'Ivoire. Diagnostic performance of each test was assessed using Quantitative Buffy Coat as the parasitological reference and immune trypanolysis as the serological reference test. According to the parasitological data, CATT-EDTA on 10 microl and LATEX/T. b. gambiense on blood diluted 1:4, detecting all confirmed cases with good specificity (respectively 94.6% and 98.1%) yielded better results than the classical CATT did (one false negative and 92.5% specific). However, when immune trypanolysis data and feasibility are taken into account, the classical CATT remains the test of choice for mass screening under the given field conditions.

Agglutination Tests↗
PubMed1992

Enhancement of chest images by automatic adaptive spatial filtering.

Postprocessing of the image data is an exciting capability of digital radiography that may improve diagnostic performance. We present a new algorithm that selectively enhances edges and contrast in both lungs and mediastinum while minimally amplifying noise in chest images. Using different size kernels, two smoothed images are generated from the original chest image. The two regions of interest (lungs and mediastinum) are identified based on the distribution of pixel values in the image. A modified nonlinear unsharp mask subtraction technique is then applied. The resulting image has enhanced high- and middle-frequency information in the mediastinum without distorting lung parenchyma or significantly enhancing noise. We consider that the technique employed in this study could be suitable for routine use although its true effectiveness in improving diagnostic accuracy awaits observer-performance evaluation that is currently under way.

Adult↗
PubMed1992

Pulmonary thallium-201 uptake following dipyridamole-exercise combination compared with single modality stress testing.

Angiographic and clinical determinants of pulmonary uptake of thallium-201 were assessed in a laboratory setting where supine bicycle exercise is used for stress testing in the absence of limiting pharmacologic or physical factors, and where symptom-limited exercise is added to intravenous dipyridamole infusion in other cases. Angiographic correlation was available in 400 patients, including 130 tested with exercise, 94 in whom only handgrip or abbreviated bicycle exercise could be used after dipyridamole, and 176 in whom intravenous dipyridamole was combined with a significant level of exercise. For each test mode, lung/myocardial ratios on the immediate image were highly correlated (p less than or equal to 0.001) with a score based on the number of critical coronary artery stenoses, with grading by contrast ventriculography, and with the number of stenosed (greater than or equal to 50%) arteries; relationships (p less than 0.05) to history of myocardial infarction and to gender were also present. Multiple regression analysis showed the critical stenosis score and ventricular dysfunction to be the only significant determinants. When dipyridamole based tests were compared with exercise, curves of receiver-operating characteristics showed a tendency to better diagnostic performance. When dipyridamole is incorporated in stress testing, the value of increased lung uptake as an ancillary diagnostic sign is similar to that established for exercise.

Analysis of Variance↗
PubMed1999

99Tcm-MIBI scintimammography in 300 consecutive patients: factors that may affect accuracy.

We evaluated the diagnostic yield of 99Tcm-MIBI scintimammography in a relatively large series of consecutive patients referred for breast surgery on the basis of physical examination or mammogram. 99Tcm-MIBI uptake was correlated to tumour size, receptor status, neovascularity, proliferating activity, P-170 glycoprotein expression and the patient's gonadal state. Three hundred consecutive patients referred to our institution, with either a positive mammogram or a palpable mass, were entered into the study. All patients underwent 99Tcm-MIBI scintimammography. Pathological status was obtained after surgery in all patients. Breast cancer was diagnosed in 218 (73%) patients. The MIBI scan was positive in 89% (194/218) cancer patients and in 17% (14/82) of patients with benign masses (false-positives); the scan was negative in 24 (11%) cancer patients (false-negatives). The sensitivity of MIBI scintigraphy was higher for tumours > 1 cm (95 vs 48% in lesions < or = 1 cm) and in pre-menopausal women (95 vs 85%). Conversely, the specificity was better for lesions < 1 cm (100%) and in post-menopausal women (89%). The positive predictive value of MIBI scan was good both in small (< 1 cm) and large tumours (100% and 93%, respectively) and slightly modified by gonadal state (89% and 96% in pre- and post-menopausal state). The negative predictive value was unsatisfactory, especially in small tumours and in older patients. The diagnostic performance increased stratifying data for tumour size, indicating that lesion size is a major determinant in the diagnostic accuracy of MIBI scintimammography. We conclude that 99Tcm-MIBI scintimammography is useful in the diagnostic evaluation of young patients, because it can select patients for further invasive diagnostic procedures. In older patients, a positive 99Tcm-MIBI scan is highly suggestive of malignancy and might be an indication for surgery. In the case of a negative scan, biopsy is advisable given the poor negative predictive value. Small tumour size and a well-differentiated histotype characterize false-negative cases.

Adult↗
PubMed2003

Best threshold for diagnosis of stenosis or thrombosis within six months of access flow measurement in arteriovenous fistulae.

Canadian clinical practice guidelines recommend performing angiography when access blood flow (Qa) is <500 ml/min in native vessel arteriovenous fistulae (AVF), but data on the value of Qa that best predicts stenosis are sparse. Because correction of stenosis in AVF improves patency rates, this issue seems worthy of investigation. Receiver-operating characteristic curves were constructed to examine the relationship between different threshold values of Qa and stenosis in 340 patients with AVF. Stenosis was defined by the composite outcome of access failure or angiographic stenosis occurring within 6 mo of the first Qa measurement. The Qa value was then classified as true negative, true positive, false negative, or false positive for stenosis. An additional analysis was performed in which Qa was corrected for systolic BP before assigning it to one of the four diagnostic categories. The area under the curve for the composite definition of stenosis was 0.86. Graphically, Qa thresholds of <500 and <600 ml/min had similar efficacy for detecting stenosis or access failure within 6 mo, and both seemed superior to <400 ml/min. However, the frequency of the composite definition of stenosis among AVF with Qa between 500 and 600 ml/min was only 6 (25%) of 24, as compared with 58 (76%) of 76 when Qa was <500 ml/min. This suggests that most lesions that would be found using a threshold of <600 ml/min occurred in AVF with Qa <500 ml/min and that the small gain in sensitivity associated with the <600-ml/min threshold would be outweighed by the reduced specificity compared with <500 ml/min. Correcting Qa for BP did not improve diagnostic performance or change these results, which were consistent in several sensitivity analyses. Qa measurements seemed to predict stenosis or incipient access failure equally well in groups defined by diabetic status, gender, and AVF location. In conclusion, it was found that Qa <500 ml/min seems to be the most appropriate threshold for performing angiography in patients with native vessel AVF. It is recommended that clinicians arrange angiography when Qa is <500 ml/min in AVF.

Arteriovenous Shunt, Surgical↗
PubMed2005

MDRD equations for estimation of GFR in renal transplant recipients.

After renal transplantation monitoring and detection of slight-to-moderate changes in GFR is a prerequisite for an optimal patient management. Recently, several equations to estimate GFR were developed and verified in the MDRD study cohort. However, little is known about the application of the MDRD formulas in the setting of renal transplantation. We prospectively conducted a study of the GFR estimates of the Cockcroft and Gault (C&G), MDRD6-, MDRD7 and the abbreviated MDRD (aMDRD) with the true GFR as measured by (99m)Tc-DTPA clearance in 95 consecutive patients 6.5, 5.3-7.7 years (mean, 95% CI) after renal transplantation. On average the DTPA clearance was 37.4, 34.4-40.4 mL/min/1.73 m(2), which differed significantly from estimates of GFR by C&G (52.6, 48.3-56.9 mL/min/1.73 m(2)), MDRD7 (44.8, 40.7-49.0 mL/min/1.73 m(2)), MDRD6 (43.8, 39.9-47.7 mL/min/1.73 m(2)) and aMDRD (46.6, 42.4-50.9 mL/min/1.73 m(2)). Bias was lowest for MDRD6 (6.4 mL/min/1.73 m(2)) and highest for C&G (15.2 mL/min/1.73 m(2)). Precision was similar for MDRD7 and aMDRD (10.6 and 11.1 mL/min/1.73 m(2)) but significantly better for MDRD6 (8.6 mL/min/1.73 m(2); p < 0.035). Accuracy within 50% of real GFR was 55.8% for C&G, 83.2% for aMDRD, 87.4% for MDRD7 and 90.5% for MDRD6. MDRD equations perform significantly better than the commonly used C&G formula. Moreover, the MDRD6 equation provides the best diagnostic performance, and should therefore be preferred in renal transplant recipients.

Adult↗
PubMed2005

Diagnostic value of ultrasonography in the evaluation of blunt abdominal trauma.

PURPOSE: To evaluate the diagnostic value of ultrasonography (US) in detecting intraabdominal injuries in patients with blunt abdominal trauma. MATERIALS AND METHODS: Blunt trauma patients admitted to the emergency department from January 2002 to August 2003 were retrospectively evaluated. A total of 454 patients with blunt abdominal trauma who underwent US examination were included. Ultrasonography results were compared with findings of CT, diagnostic peritoneal lavage, laparotomy and clinical course. Sensitivity, specificity, positive and negative predictive values of US in detecting free fluid, intraabdominal parenchymal organ injury or both were calculated. RESULTS: Computed tomography, diagnostic peritoneal lavage and laparotomy results showed that intraabdominal organ injury was present in 37 of 454 patients. Ultrasonography examinations were positive in 51 patients. True-positive findings were seen in 32 of these patients. In these 32 patients, US examination showed free fluid in 19, fluid and abdominal organ injury in 11 and only abdominal organ injury in 2. Sensitivity, specificity, positive predictive value, negative predictive value and accuracy of US in detecting intraabdominal injury were 86.5%, 95.4%, 62.7%, 98.7% and 94.7%, respectively. CONCLUSION: Ultrasonography has high diagnostic performance in the screening of patients with blunt abdominal trauma. Abdominal US is a useful and valuable diagnostic tool after clinical evaluation in patients with blunt abdominal trauma. Because of its high negative predictive value, we recommend that clinical follow up is adequate for patients whose US results are negative for intraabdomial organ injury.

Abdominal Injuries↗
PubMed1992

An evaluation of maximum likelihood-expectation maximization reconstruction for SPECT by ROC analysis.

A ROC study was performed in order to evaluate whether the maximum likelihood expectation maximization (ML-EM) reconstruction algorithm improves diagnostic performance compared to the conventional filtered backprojection method in SPECT. Several implementations of the algorithm were tested including 25 and 50 iteration stopping points, with and without nonuniform attenuation compensation, and with and without Metz filtering. Filtered backprojection was with Metz filter and without attenuation compensation. The test data were computer simulated to model cardiac 201Tl SPECT. The data incorporated the effects of nonuniform attenuation, distance-dependent collimator response, and scatter. Patient CT images provided realistic anatomy and attenuation information for the data simulation. Four observers each viewed 120 images for each of the reconstruction methods. Lesion detectability with ML-EM increased with Metz filtering and decreased with nonuniform attenuation compensation. The best MIL-EM implementation, 50 iterations with Metz filtering and without attenuation compensation, was not statistically better than filtered backprojection.

Algorithms↗
PubMed1997

Influence of an unaccustomed increase in training volume vs intensity on performance, hematological and blood-chemical parameters in distance runners.

The hypothesis was tested that high-volume endurance training can be monitored using hematological and blood-chemical parameters as markers of an early stage in the overtraining process. Eight experienced distance runners participated in a prospective, experimental, controlled study. The study consisted of an unaccustomed average 103% increase in training volume (ITV) within 4 weeks (average final volume: 174.6 km per week). A year later, 9 runners performed the additional 4-week control study that consisted of an unaccustomed average 152% increase in intensive training measures (ITI). Average total volume amounted to 61.7 km (week 1) and 84.7 km (week 4). Seven athletes participated in both studies. Simultaneously to performance diagnostics, a comprehensive pattern of hematological and blood-chemical parameters was determined. During ITV, submaximum running performance was improved after 2 weeks, stopped improving between week 3 and 4; maximum performance did not increase rather was decreased after week 4 compared to baseline as indication of an early stage in the overtraining process. During ITI, submaximum and maximum running performances increased continuously. In contrast to ITI, the following parameters decreased significantly during ITV: White blood cell count, serum iron, ferritin, VLDL-(very low density lipoproteins), LDL (low density lipoproteins)-cholesterol, albumin, resting and maximum free fatty acid, maximum lactate, resting, submaximum and maximum glucose, summed amino acid, resting, submaximum and maximum ammonia concentrations, whereas prothrombin time increased significantly. During high-volume endurance training a multifactorial and longitudinal approach considering either a performance incompetence and an individually different range of symptoms and alterations in hematological and blood-chemical parameters can help to recognize an early stage in the overtraining process.

Blood Chemical Analysis↗
PubMed1993

[Diagnostic vitrectomy for chronic uveitis].

Uveitis is diagnosed by ophthalmologic and systemic examination, but it may be difficult to diagnose accurately in some chronic cases. We performed diagnostic and therapeutic vitrectomy for chronic uveitis in 6 eyes of 4 patients, and examined vitreous specimens with immunohistochemical staining. Visual acuity improved in all cases due to clearing up of the vitreous cells. One patient had sarcoidosis, one had B cell malignant lymphoma (ocular reticulum cell sarcoma), and two had reactive lymphoid hyperplasia. Vitrectomy for chronic uveitis is useful for diagnosis and improvement of vision, and we recommend immunohistological staining of vitreous specimens. Particularly, when intraocular lymphoma is suspected, vitrectomy must be performed early.

Aged↗
PubMed2001

Non-invasive management of patients with suspected ectopic pregnancy: a survey among Dutch gynaecologists.

OBJECTIVE: To investigate if implementation of a non-invasive diagnostic work up of patients with suspected ectopic pregnancy, involving transvaginal sonography and serum human chorionic gonadotrophin (hCG) measurement decreases the likelihood of performing diagnostic laparoscopies. STUDY DESIGN: We interviewed 27 Dutch gynaecologists using 16 structured case summaries in a fractional factorial design. Each case summary concerned a hypothetical patient with suspected ectopic pregnancy. For each case presentation, the gynaecologists were asked for their inclination to perform laparoscopy. RESULTS: There were substantial differences in the degree to which data from a non-invasive work-up influenced the decision to perform a laparoscopy. Some gynaecologists would perform laparoscopy in all 16 patients at the first visit, whereas others would initially admit none of them. CONCLUSION: Dutch gynaecologists seem to be familiar with a non-invasive diagnostic approach in women with suspected ectopic pregnancy. However, there are considerable differences in management approach probably due to individual variability in weighing the risks and benefits of expectant management.

Chorionic Gonadotropin↗
PubMed2026

Integrated bioinformatics analysis reveals cross-talking hub genes and therapeutic agents between sepsis and acute myocardial infarction.

BACKGROUND: Sepsis and acute myocardial infarction (AMI) are two significant diseases that may share overlapping etiological mechanisms. This study aims to systematically identify core genes common to both conditions and to explore their potential as therapeutic targets and drug candidates through an integrative analysis of clinical data and bioinformatics. METHODS: The AMI dataset was obtained from the GEO database, and RNA sequencing data were collected from blood samples of patients with sepsis at our hospital. Common genes were identified using differential expression gene analysis (DEG) and weighted gene co-expression network analysis (WGCNA). Functional enrichment analyses, including Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, were performed. A protein-protein interaction (PPI) network was constructed, and hub genes were identified using the MCC/Degree algorithm. Diagnostic value was assessed via receiver operating characteristic curve analysis. Immune infiltration patterns, single-cell sequencing data, and molecular docking simulations were employed to evaluate immune relevance and identify potential therapeutic compounds. RESULTS: A total of 417 genes were identified between sepsis and AMI, with enrichment analysis revealing significant involvement in inflammatory responses. Three hub genes-JAK2, MYD88, and TIMP1-were selected for further investigation. ROC curves confirmed their strong diagnostic performance for both diseases. Immune infiltration analysis showed that these core genes were significantly correlated with the infiltration levels of various immune cell types. Molecular docking indicated that quercetin exhibited stable binding affinity with the proteins encoded by these genes. qPCR validation further confirmed the upregulation of these three genes, supporting the anti-inflammatory effects of quercetin as a potential targeted therapy. CONCLUSION: JAK2, MYD88, and TIMP1 were identified as shared core genes in sepsis and AMI. These genes not only serve as potential diagnostic biomarkers but also offer novel targets for developing common therapeutic strategies for both conditions. Furthermore, quercetin emerges as a promising candidate for targeted treatment.

Humans↗
PubMed1994

Initial feasibility studies using single-shot EPI for the detection of focal liver lesions.

Echo planar MR imaging (EPI) has been developed to completely eliminate motion artifacts and is currently being prepared for implementation into clinical MR systems. Thus, the purpose of this study was to evaluate the clinical utility of EPI in the detection of focal liver lesions and to compare EPI with in the detection of focal liver lesions and to compare EPI with contrast-enhanced CT. EPI studies were performed on an experimental 1.0 Tesla whole body system using fat-suppressed single-shot spin echo (SE) and inversion recovery (IR) pulse sequences. A total of 26 liver tumors in 12 patients scheduled for liver resection were prospectively examined and correlated with intraoperative ultrasound, surgery, and pathology as the gold standard. Quantitative analysis of EPI was performed by means of liver signal-to-noise and tumor-liver contrast-to-noise calculations. Diagnostic performance compared with contrast-enhanced CT was assessed by means of ROC analysis. Lesion-liver contrast was highest with EPI SE at a TE-time of 70 ms and this technique showed best lesion detectability as measured by area under curve (AUC) values. Among EPI techniques, the IR sequence with an inversion time of 300 ms to null the liver signal showed high lesion-liver contrast but all four reviewers reported problems assessing liver anatomy. Improved EPI techniques may prove useful for screening of focal liver lesions.

Adult↗
PubMed2000

Present issues in the determination of troponins and other markers of cardiac damage.

OBJECTIVE: To review some of the recently proposed improvements and the corresponding apparent issues in the field of biochemical markers of cardiac damage. CONCLUSIONS: The continuous development of new analytical tools for the biochemical evaluation of patients with suspected myocardial injury brings without doubt new challenges of careful technological evaluation, implementation, and standardization but it may also provide a unique opportunity to markedly enhance our diagnostic performance in the clinical setting of acute coronary syndrome.

Biomarkers↗
PubMed1998

Short-term follow-up by serology of patients given antibiotic treatment for Helicobacter pylori infection.

Helicobacter pylori serology and in particular enzyme-linked immunosorbent assays for the measurement of immunoglobulin G (IgG) antibody titers form an accurate means of diagnosing H. pylori infection in patients before treatment. H. pylori serology is of limited value in monitoring treatment because of the slow decline in antibody titers. In the present study we aimed to measure the most suitable moment after antibiotic treatment at which serology should be used to monitor treatment. Sixty-four patients who had nonulcer dyspepsia and H. pylori infection and who underwent upper gastrointestinal endoscopy because of persistent dyspeptic symptoms were included in the study. H. pylori cure was confirmed by histology and culture 5 weeks after the completion of the antibiotic treatment. Serological examination was performed before therapy and at 5 weeks, 10 weeks, and 1 year after the completion of antibiotic treatment. Diagnostic performance was assessed by receiver-operating characteristic analysis. The areas under the receiver-operating characteristic curves of the H. pylori antibody titers at 5 weeks, 10 weeks, and 1 year after the completion of treatment were 0.53 (95% confidence interval [CI], 0.36 to 0.69), 0.60 (95% CI, 0.43 to 0.76), and 0.78 (95% CI, 0.63 to 0.93), respectively. The areas under the receiver-operating characteristic curves of the changes in H. pylori IgG antibody titers at 5 weeks, 10 weeks, and 1 year after the completion of treatment in comparison with the pretreatment titers were 0.85 (95% CI, 0.72 to 0.97), 0.96 (95% CI, 0.89 to 1.0), and 1.0 (95% CI, not estimable), respectively. We conclude that serology forms a useful means of monitoring treatment in patients with nonulcer dyspepsia and H. pylori infection as early as 10 weeks and maybe even sooner after the completion of treatment for the infection.

Anti-Bacterial Agents↗
PubMed2000

[French translation and validation of the Edinburgh Questionnaire for the diagnosis of intermittent claudication].

Obliterative arterial disease of the lower limbs is diagnosed by simple, reproducible, sensitive and non-invasive methods. One of these, a questionnaire for the diagnosis on intermittent limping, is a method of choice. Until recent years, the only validated questionnaire was the one proposed by the World Health Organisation. This was criticised a lot, especially for its lack of sensitivity. Recently, a Scottish group proposed an improvement in the diagnostic performance of this questionnaire by carrying out several changes. This new version, called the Edinburgh Questionnaire, has promising diagnostic qualities. The authors present a French version of this questionnaire. This French translation was validated in 105 patients referred for diagnosis of obliterative lower limb arterial disease. A sensitivity of 86.5%, a specificity of 95.6%, a positive predictive value of 91.4% and a negative predictive value of 92.9% of this French version are comparable to the results obtained with the English version. Therefore, the authors suggest using this questionnaire in epidemiological and public health studies in France.

Aged↗