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False-positive Findings (false-positive + finding)
Selected AbstractsFalse-positive analysis of functional MRI during simulated deep brain stimulation: A phantom studyJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2008Ho-Ling Liu PhD Abstract Purpose To investigate the false-positive activations/deactivations in functional MRI (fMRI) of deep brain stimulation (DBS) using a phantom. Materials and Methods fMRI experiments were performed on a 1.5T scanner using a single-shot gradient-echo echo-planar imaging (GE-EPI) sequence (TR/TE/FA = 6000 msec/60 msec/90°) on an agar-gel phantom inserted with DBS electrodes. During the experimental blocks, two-second stimuli were delivered during the interscan waiting time (ISWT), which was adjusted by changing the number of slices acquired within the TR (3500 msec with 30 slices and 5160 msec with 10 slices). Data were analyzed using SPM2 software, and the false-positive voxels were detected with five different P-value thresholds. Results The number of false-positive voxels in experimental conditions had no significant differences from those in control conditions with either long or short ISWT, which increased with the P-value threshold from zero at P < 0.0001 to approximately 40 at P < 0.05. The pattern of increasing number of false-positive reactions along with P-value was similar between all conditions. Conclusion False-positive findings from fMRI with similar experimental design can be well controlled with a statistical threshold of P < 0.001 or tighter. The short ISWT of 3500 msec did not increase false-positive reactions compared to the long ISWT of 5160 msec. J. Magn. Reson. Imaging 2008;27:1439,1442. © 2008 Wiley-Liss, Inc. [source] Respiratory cytology: Differential diagnosis and pitfallsDIAGNOSTIC CYTOPATHOLOGY, Issue 4 2010F.R.C.P.C., Ph.D., Reda S. Saad M.D. Abstract Pulmonary cytology can be challenging and has its share of diagnostic pitfalls. Reactive atypia can occasionally be alarming, leading to diagnostic pitfall for a false-positive diagnosis of malignancy, even for experienced cytopathologists (Naryshkin and Young, Diagn Cytopathol 1993;9:89,97). In addition, cytologic preparations can show an absence of architectural clues, leading to diagnostic difficulties. Some conditions can cytologically as well as clinically and radiographically mimic malignancies, making these pitfalls even more frequent (Bedrossian et al., Lab Med 1983;14:86,95). A recent report stated that "no laboratory that aims to make definitive diagnoses in pulmonary cytology can be spared from false-positive results"(Policarpio-Nicolas and Wick, Diagn Cytopathol 2008;36:13,19). A false-positive finding could produce unnecessary treatment and morbidity, whereas false-negative diagnosis could result in delayed diagnosis and treatment. This review analyzes and illustrates cellular changes and benign entities that can mimic malignancy in respiratory cytology as well as neoplasms that could lead to a false-negative diagnosis. In addition, some specific challenging and difficult aspects in classification of pulmonary malignancies will be discussed. Guidelines and clues are presented to avoid such pitfalls. Diagn. Cytopathol. 2010. © 2009 Wiley-Liss, Inc. [source] False-positive liquid chromatography/tandem mass spectrometric confirmation of sebuthylazine residues using the identification points system according to EU directive 2002/657/EC due to a biogenic insecticide in tarragonRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 8 2009Andreas Schürmann In pesticide residue analysis using liquid chromatography/tandem mass spectrometry (LC/MS/MS) the confirmation of a sebuthylazine finding in a tarragon (Artemisia dranunculus) sample was demonstrated to be false positive. A coeluting interfering matrix compound produced product ions in MS/MS analysis, perfectly corresponding to the multiple reaction monitoring (MRM) of two sebuthylazine transitions. Using the EU directive 2002/657/EC which regulates the confirmation of suspected positive findings would have resulted in a false-positive finding. A third LC/MS/MS transition with a deviant ion ratio and a gas chromatography (GC)/MS/MS analysis revealed the false-positive results. With optimized high resolving ultra-performance liquid chromatography (UPLC) conditions it was possible to separate spiked sebuthylazine from the interfering matrix compound. Using its exact mass and isotope ratios from LC/time-of-flight (TOF) MS measurements, the compound was identified as nepellitorine, a , not surprising , endogenous alkamide in tarragon (Arthemisia dranunculus). False-positive results, especially in heavy matrix samples such as herbs, can be dealt with by further confirmatory analysis, e.g. a third transition, GC analysis if possible or more advantageous by an orthogonal criterion like exact mass. Copyright © 2009 John Wiley & Sons, Ltd. [source] Improved correction for population stratification in genome-wide association studies by identifying hidden population structures,GENETIC EPIDEMIOLOGY, Issue 3 2008Qizhai Li Abstract Hidden population substructure can cause population stratification and lead to false-positive findings in population-based genome-wide association (GWA) studies. Given a large panel of markers scanned in a GWA study, it becomes increasingly feasible to uncover the hidden population substructure within the study sample based on measured genotypes across the genome. Recognizing that population substructure can be displayed as clustered and/or continuous patterns of genetic variation, we propose a method that aims at the detection and correction of the confounding effect resulting from both patterns of population substructure. The proposed method is an extension of the EIGENSTRAT method (Price et al. [2006] Nat Genet 38:904,909). This approach is computationally feasible and easily applied to large-scale GWA studies. We show through simulation studies that, compared with the EIGENSTRAT method, the new method requires a smaller number of markers and yields a more appropriate correction for population stratification. Genet. Epidemiol. 2007. Published 2007 Wiley-Liss, Inc. [source] MR colonography for the assessment of colonic anastomosesJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2006Waleed Ajaj MD Abstract Purpose To assess colonic anastomoses in patients after surgical treatment by means of MR colonography (MRC) in comparison with conventional colonoscopy (CC). Materials and Methods A total of 39 patients who had previously undergone colonic resection and end-to-end-anastomosis were included in the study. MRI was based on a dark-lumen approach. Contrast-enhanced T1-weighted (T1w) three-dimensional (3D) images were collected following the rectal administration of water for colonic distension. The MRC data were evaluated by two radiologists. The criteria employed to evaluate the anastomoses included bowel wall thickening and increased contrast uptake in this region. Furthermore, all other colonic segments were assessed for the presence of pathologies. Results In 23 and 20 patients the anastomosis was rated to be normal by MRC and CC, respectively. In three patients CC revealed a slight inflammation of the anastomosis that was missed by MRI. A moderate stenosis of the anastomosis without inflammation was detected by MRC in five patients, which was confirmed by CC. In the remaining 11 patients a relevant pathology of the anastomosis was diagnosed by both MRC and CC. Recurrent tumor was diagnosed in two patients with a history of colorectal carcinoma. In the other nine patients inflammation of the anastomosis was seen in seven with Crohn's disease (CD) and two with ulcerative colitis. MRC did not yield any false-positive findings, resulting in an overall sensitivity/specificity for the assessment of the anastomosis of 84%/100%. Conclusion MRC represents a promising alternative to CC for the assessment of colonic anastomoses in patients with previous colonic resection. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source] Adjusted Scaling of FDG Positron Emission Tomography Images for Statistical Evaluation in Patients With Suspected Alzheimer's DiseaseJOURNAL OF NEUROIMAGING, Issue 4 2005Ralph Buchert PhD ABSTRACT Background and Purpose. Statistical parametric mapping (SPM) gained increasing acceptance for the voxel-based statistical evaluation of brain positron emission tomography (PET) with the glucose analog 2-[18F]-fluoro-2-deoxy-d-glucose (FDG) in patients with suspected Alzheimer's disease (AD). To increase the sensitivity for detection of local changes, individual differences of total brain FDG uptake are usually compensated for by proportional scaling. However, in cases of extensive hypometabolic areas, proportional scaling overestimates scaled uptake. This may cause significant underestimation of the extent of hypometabolic areas by the statistical test. Methods. To detect this problem, the authors tested for hyper metabolism. In patients with no visual evidence of true focal hypermetabolism, significant clusters of hypermetabolism in the presence of extended hypometabolism were interpreted as false-positive findings, indicating relevant overestimation of scaled uptake. In this case, scaled uptake was reduced step by step until there were no more significant clusters of hypermetabolism. Results. In 22 consecutive patients with suspected AD, proportional scaling resulted in relevant overestimation of scaled uptake in 9 patients. Scaled uptake had to be reduced by 11.1%± 5.3% in these cases to eliminate the artifacts. Adjusted scaling resulted in extension of existing and appearance of new clusters of hypometabolism. Total volume of the additional voxels with significant hypometabolism depended linearly on the extent of the additional scaling and was 202 ± 118 mL on average. Conclusions. Adjusted scaling helps to identify characteristic metabolic patterns in patients with suspected AD. It is expected to increase specificity of FDGPET in this group of patients. [source] Screening for Intracranial Stenosis With Transcranial Doppler: The Accuracy of Mean Flow Velocity ThresholdsJOURNAL OF NEUROIMAGING, Issue 1 2002Robert A. Felberg MD ABSTRACT Background. Patients with 50% intracranial arterial stenosis may require more intensive therapies for stroke prevention. Transcranial Doppler (TCD) is a convenient noninvasive screen for intracranial stenosis. The accuracy of different mean flow velocity (MFV) thresholds for determining the degree of stenosis remains uncertain. Methods. The authors prospectively compared the accuracy of TCD criteria and MFV thresholds to magnetic resonance, computed tomography, and digital subtraction angiography in patients with symptoms of recent or remote stroke or transient ischemic attack. Stenosis on angiography was measured as 0%, <50%, or ,50% diameter reduction. Results. Of 136 consecutive patients, 33 (24%) had distal internal carotid artery (ICA), middle cerebral artery (MCA), posterior cerebral artery, or basilar artery stenosis on angiography (14 patients [10%] were excluded due to incomplete TCD examinations, mainly from a lack of temporal windows). TCD showed 31 true-positive, 9 false-positive, 2 false-negative, and 94 true-negative studies. For all vessels, TCD had a sensitivity of 93.9% (confidence interval [CI] = 89%-98%), a specificity of 91.2% (CI = 87%-96%), a positive predictive value (PPV) of 77.5%, and a negative predictive value (NPV) of 97.9%. The trade-off in sensitivity and specificity for MCA MFV thresholds was as follows: MFV ,80 cm/s had a sensitivity of 100%, a specificity of 96.9% (CI = 94%-99%), a PPV of 84%, and an NPV of 100%. MFV,100 cm/s had a sensitivity of 100%, a specificity of 97.9% (CI = 96%-99%), a PPV of 88.8%, and an NPV of 94.9%. MFV,120 cm/s had a sensitivity of 68.7% (CI = 61%-78%), a specificity of 100%, a PPV of 100%, and an NPV of 94.9%. Reasons for false-positive findings include collateralization of flow in the presence of proximal ICA stenosis and prestenotic to stenotic MCA velocity ratios of 1:,2. Conclusion. TCD is both sensitive and specific in identifying ,50% intracranial arterial stenosis. A MFV threshold cutoff of 100 cm/s has an optimal sensitivity and specificity trade-off for ,50% MCA stenosis. To help avoid false-positive results, a prestenotic to stenotic MCA velocity ratio of 1:,2 should be used in addition to the MFV threshold. [source] Additional reverse transcription,polymerase chain reaction of peripheral slices is not superior to analysis of the central slice in sentinel lymph nodes from melanoma patientsBRITISH JOURNAL OF DERMATOLOGY, Issue 3 2004H-J. Blaheta Summary Background The status of the sentinel lymph node (SLN) is an important prognostic factor in patients with cutaneous melanoma. Reverse transcription,polymerase chain reaction (RT,PCR) has been used as a sensitive means of detecting tumour cells in SLNs. Objectives To determine whether RT,PCR analysis of the SLN using both the central and the peripheral slices is more sensitive than molecular analysis of the central slice only. Methods Eighty-three SLNs from 59 patients with primary cutaneous melanoma were identified by SLN mapping. All SLNs were bisected along their longitudinal axis to produce two equal halves. One half was used for histology and immunohistochemistry, and the other was analysed by RT,PCR for tyrosinase and MelanA. Parallel to the longitudinal axis, one central slice (approximately 2 mm in thickness) was cut manually. This central slice was used for our standard RT,PCR protocol. In the current study, up to eight additional peripheral slices (each approximately 2 mm in thickness) were cut parallel to the existing cut surface. These peripheral slices were analysed by additional RT,PCR. Results Standard RT,PCR of the central slice yielded positive results in 34 of 59 patients (57%). Additional RT,PCR of peripheral slices demonstrated positive findings in six additional patients (10%) who were initially negative by standard RT,PCR of the central slice. In detail, seven of those 34 patients positive by standard RT,PCR of the central slice had positive histological findings. In each of these seven patients, RT,PCR was positive both in the central slice as well as in the peripheral slices. The remaining 27 patients with positive RT,PCR results of the central slice showed negative histological findings. Only nine (33%) of these 27 patients had a positive RT,PCR also in the peripheral slices. Finally, all 25 patients with negative RT,PCR results in the central slice showed negative histological findings. Six of these patients (24%) revealed positive RT,PCR results on the analysis of peripheral slices. However, three of these patients expressed only MelanA but not tyrosinase. Thirty lymph nodes from 24 nonmelanoma patients served as negative controls for RT,PCR. In three of these 24 patients (13%) expression of MelanA but not tyrosinase was detected by RT,PCR. Conclusions Molecular analysis of peripheral slices yielded six additional patients (10%) positive by RT,PCR who were initially negative by standard RT,PCR of the central slice. However, three of these six patients were found to express only MelanA but not tyrosinase. As MelanA expression was also found in 13% of control lymph nodes, positive MelanA expression alone in SLNs of melanoma patients requires cautious interpretation in order to avoid false-positive findings. Thus, additional molecular processing of peripheral slices did not significantly increase the number of patients with RT,PCR-positive SLNs. [source] Combining a symptoms index with CA 125 to improve detection of ovarian cancerCANCER, Issue 3 2008M. Robyn Andersen PhD Abstract BACKGROUND. The current study sought to examine whether an index based on the specific pattern of symptoms commonly reported by women with ovarian cancer could be used in combination with CA 125 to improve the sensitivity or specificity of experimental methods of screening for ovarian cancer. METHODS. A prospective case-control study design was used. Participants included 254 healthy women at high risk for disease because of family history, and 75 women with ovarian cancer. Logistic regression analysis was used to determine whether the symptom index predicted cancer. RESULTS. Symptom index information was found to make a significant independent contribution to the prediction of ovarian cancer after controlling for CA 125 levels (P<.05). The combination of CA 125 and the symptom index identified 89.3% of the women with cancer, 80.6% of the early,stage cancers, and 95.1% of the late-stage cancers. The symptom index identified cancer in 50% of the affected women who did not have elevated CA 125 levels. Unfortunately, 11.8% of the high-risk women without cancer also received a positive symptom index score. CONCLUSIONS. The addition of a symptom index to CA 125 created a composite index with a greater sensitivity for the detection of ovarian cancer than CA 125 alone and identified >80% of women with early-stage disease. A composite marker such as this could serve as a first screen in a multistep screening program in which false-positive findings are identified via transvaginal sonography before referral for surgery, leading to an adequate positive predictive value for the multistep program. Cancer 2008. © 2008 American Cancer Society. [source] | ||||||||||