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J E Lenz

Publications and source records attributed to J E Lenz.

5 recordsLinked to original sources
PubMed1997

A general statistical framework for frequency-domain analysis of EEG topographic structure.

A wide variety of rhythmic electrophysiological phenomena--including driven, induced, and endogenous activities of cortical neuronal masses--lend themselves naturally to analysis using frequency--domain techniques applied to multichannel recordings that discretely sample the overall spatial pattern of the rhythmic activity. For such cases, a large but so far poorly utilized body of statistical theory supports a third major approach to topographic analysis, complementing the more familiar mapping and source-recovery techniques. These methods, many of which have only recently become computationally feasible, collectively provide general solutions to the problem of detecting and characterizing systematic differences that arise--not only in the spatial distribution of the activity, but also in its frequency-dependent between-channel covariance structure--as a function of multiple experimental conditions presented in conformity with any of the conventional experimental designs. This application-oriented tutorial review provides a comprehensive outline of these resources, including: (1) real multivariate analysis of single-channel spectral measures (and measures of between-channel relationships such as coherence and phase), (2) complex multivariate analysis based on multichannel Fourier transforms, and (3) complex multivariate analysis based on multichannel parametric models. Special emphasis is placed on the potential of the multichannel autoregressive model to support EEG (and MEG) studies of perceptual and cognitive processes.

Cerebral Cortex↗
PubMed1996

Carotid duplex criteria for a 60% or greater angiographic stenosis: variation according to equipment.

PURPOSE: The purpose of this study was to evaluate the carotid duplex criteria for a > or = 60% angiographic internal carotid artery (ICA) stenosis and the degree of variation among duplex scanners. METHODS: Carotid duplex criteria for a > or = 60% angiographic stenosis were evaluated in two ICAVL-accredited vascular laboratories with different brands of duplex scanners (Siemens-Quantum and Diasonics in Laboratory A, ATL and Diasonics in Laboratory B). Analysis was performed for 360 carotid bifurcations in 180 consecutive patients who had concurrent angiographic and duplex evaluation. Blinded angiogram evaluation was performed with precision electronic calipers on magnified views, with stenosis calculated by criteria of the Asymptomatic Carotid Atherosclerosis Study and the North American Symptomatic Carotid Endarterectomy Trial. Duplex data included internal carotid artery peak systolic velocity (ICA PSV), ICA end-diastolic velocity, and the ratio of ICA PSV to common carotid artery (CCA) PSV (ICA/CCA ratio). RESULTS: The most accurate determination of a > or = 60% ICA stenosis was obtained with ICA/CCA ratio and ICA PSV, but the optimal threshold differed for all four scanners. The optimal ICA/CCA ratio varied from 2.6 to 3.3, and the optimal ICA PSV varied from 190 to 240 cm/sec. All four scanners produced criteria that give a positive predictive value > 90% while maintaining accuracy at > or = 90%. Logarithmic transformation of duplex variables created a linear relationship between duplex values and angiographic stenosis, allowing statistical evaluation of scanner operating characteristics by linear regression analysis and analysis of covariance. This analysis revealed that the mathematic equation relating duplex values with angiographic percent stenosis was statistically different for one of the four scanners (p < 0.05). Scanner differences did not appear to be due to technologists, because the regression lines were nearly identical for the two Diasonics scanners despite use by different technologists. Ignoring the significant difference in operating characteristics for one of the four scanners would result in a mean error for predicting a 60% stenosis of 14% to 18% (equating a 46% or 78% stenosis with a 60% stenosis). CONCLUSIONS: We conclude that the correlation of duplex data with angiographic percent stenosis and the duplex criteria for a > or = 60% stenosis are machine-specific. Regression analysis can determine whether apparent differences are due to chance or significant differences in scanner characteristics. Future studies should include regression analysis according to equipment type.

Aged↗
PubMed1992

The relationship of clinical findings to CT scan evidence of adrenal gland metastases in the staging of bronchogenic carcinoma.

OBJECTIVE: To determine whether, during the staging of newly diagnosed bronchogenic carcinoma, clinical indicators predict the presence or absence of adrenal metastases detected by computerized tomographic (CT) scans. DESIGN: Retrospective review of charts and roentgenograms. SETTING: Academic medical center. PATIENTS: Two hundred five consecutive patients diagnosed with bronchogenic carcinoma, of whom 173 had sufficient data available for analysis. MEASUREMENTS: Charts were reviewed for abnormalities in three clinical categories (signs, symptoms, and routine laboratory tests) and the presence of extrapulmonary tumor spread. The CT scans were reviewed for evidence of adrenal involvement by radiologists blinded to clinical findings. MAIN RESULTS: Thirty patients had abnormal adrenal glands on CT scan. In 26 the abnormality was believed to represent adrenal metastasis, whereas in four the CT findings were consistent with adrenal adenomas. The frequency of adrenal metastases varied with the number of positive, clinical findings (chi 2 = 105.4; p < 0.001). All 26 patients with adrenal metastases had at least one clinical abnormality, and 21 (81 percent had abnormalities in either two or all three clinical categories. In 40 patients without any clinical indicators of widespread disease, none had CT evidence of adrenal metastases. The presence of adrenal metastases also varied with the extent of coexistent disease (chi 2 = 111.82; p < 0.001). Eighty-one percent (21) of the patients with and 18 percent of those without adrenal metastases had both intrathoracic and extrathoracic involvement. CONCLUSIONS: Our findings indicate that adrenal metastases are found in patients with a large tumor burden who have clinical indicators of widespread disease. We found no evidence of adrenal metastases by CT in any patient with a normal clinical evaluation. We conclude that CT scans through the adrenal glands are unnecessary when staging newly diagnosed bronchogenic carcinoma if the findings from the initial clinical evaluation are normal.

Adrenal Gland Neoplasms↗