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At least 235 records · Page 13Linked to original sources
PubMed2003

Detection limit in low-amplitude EEG measurement.

Electrocerebral inactivity for the determination of cerebral death is defined as no findings of EEG greater than the amplifier's inherent internal noise level when recording at increased sensitivity. A surface biopotential electrode contains two interfaces composed of skin gel (electrolyte) and gel electrode (metal), each forming a noise source. The power spectral density, S(f), of extremely low noise signals was obtained by means of autocorrelation and fast Fourier transformation. Interelectrode resistance, R(f), was measured with synchronous rectification. The formula of equivalent noise resistance R(n) = S(f)/4kT, where k is the Boltzmann constant and T is room temperature in Kelvin, gives a resistance that generates the thermal noise corresponding to the measured S(f). Rn/R is a parameter derived from normalization by R. When Rn/R = 1, measured noise contains thermal noise only. Meanwhile, Rn/R > 1 indicates presence of excess noise, such as 1/f, and tissue noise in addition to the thermal noise. Mean square root (Rn/R) of the scalp noise was 10.8 at 10 Hz, showing existence of excess noise. The study results suggest that it is necessary to take excess noise into consideration in the measurement of low-amplitude EEG for the determination of cerebral death.

Adult↗
PubMed2000

Comparative evaluation of two branched-DNA human immunodeficiency virus type 1 RNA quantification assays with lower detection limits of 50 and 500 copies per milliliter.

We have comparatively evaluated Quantiplex version 3.0 and version 2. 0 on 133 plasma samples and a repetitive dilution series. Version 3. 0 yielded higher human immunodeficiency virus RNA values, and the ratio of version 3.0 results to version 2.0 results decreased from 3. 47 below 1,000 copies/ml to 1.97 above 50,000 copies/ml [linear regression, log (version 3.0) = 0.915 + 0.871 x log (version 2.0); r(2) = 0.952].

DNA Probes↗
PubMed1997

Lossy (15:1) JPEG compression of digital coronary angiograms does not limit detection of subtle morphological features.

BACKGROUND: Development of the "all-digital" cardiac catheterization laboratory has been slowed by substantial computer archival and transfer requirements. Lossy data compression reduces this burden but creates irreversible changes in images, potentially impairing detection of clinically important angiographic features. METHODS AND RESULTS: Fifty image sequences from 31 interventional procedures were viewed both in the original (uncompressed) state and after 15:1 lossy Joint Photographic Expert's Group (JPEG) compression. Experienced angiographers identified dissections, suspected thrombi, and coronary stents, and their results were compared with those from a consensus panel that served as a "gold standard." The panel and the individual observers reviewed the same image sequences 4 months after the first session to determine intraobserver variability. Intraobserver agreement for original images was not significantly different from that for compressed images (89.8% versus 89.5% for 600 pairs of observations in each group). Agreement of individual observers with the consensus panel was not significantly different for original images from that for compressed images (87.6% versus 87.3%; CIs for the difference, -4.0%, 4.0%). Subgroup analysis for each observer and for each detection task (dissection, suspected thrombus, and stent) revealed no significant difference in agreement. CONCLUSIONS: The identification of dissections, thrombi, and coronary stents is not substantially impaired by the application of 15:1 lossy JPEG compression to digital coronary angiograms. These data suggest that digital angiographic images compressed in this manner are acceptable for clinical decision-making.

Coronary Angiography↗
PubMed2006

Bench evaluation of flow limitation detection by automated continuous positive airway pressure devices.

STUDY OBJECTIVE: Automatic continuous positive airway pressure (CPAP) devices that adjust the pressure delivered to the patient are now available to treat sleep-disordered breathing. Sophisticated auto-CPAP devices can detect and correct flattened inspiratory flow contours (FIFCs) associated with subtle upper airway obstruction. However, evaluations of their performance are made difficult by differences across patients and devices. We performed a bench study of five commercially available auto-CPAP devices using a breath waveform simulator to evaluate sensitivity for detecting flattened inspiratory flow. DESIGN: Five degrees of FIFC were simulated. In addition, normal and abnormal flow contours from patients published in the literature were evaluated. MEASUREMENTS AND RESULTS: One device showed autotriggering leading to CPAP increases, and another device varied the CPAP level independently from the presence of an FIFC. The three remaining devices differed regarding the detection of FIFCs and the means used to increase CPAP. CONCLUSION: Based on the characteristics of each patient, physicians must choose among devices with different thresholds of FIFC detection and different pressure responses to detection. Therefore, physicians need details on the algorithms used in auto-CPAP devices. Manufacturers should supply detailed algorithms.

Continuous Positive Airway Pressure↗
PubMed2004

Polyvinyl alcohol as a useful indicator on iodometry. (II): Temperature dependence of iodine recovery and the correction method of iodine concentration in the lower detection limit region.

In an iodometric titration method for iodine (or chlorine) analysis, the percent recovery of iodine (or chlorine) decreases in the low concentration region and at the relatively higher temperature range. We have shown that the percent recovery vs. concentration curve can be expressed by a simple empirical formula. The empirical formula contains parameters that depend on temperature and those parameters were obtained as a function of temperature. The empirical formula can be used as a correction function for experimental iodine (or chlorine) concentrations. By applying the correction function with the parameters to the experimentally obtained concentrations, we can estimate the reliable concentration in the low concentration region. Estimated concentrations were within 10% (as RSD) of the exact values after the correction in the range of 0.4 mg I2 L(-1) ([triple bond] ca. 0.1 mg as Cl2 L9-1)) - 4.4 mg I2 L(-1) ([triple bond] ca. 1.2 mg as Cl2 L(-1)) in the temperature range of 0 to 30 degrees C.

Journal Article↗
PubMed2003

[The limited detection of lung cancer on chest X-rays].

In a study of everyday clinical practice, the diagnosis 'lung cancer' was not made on the chest X-ray initially in one-fifth of the cases, even though in retrospect the lesions had been visible on the chest X-ray. In nearly half of these cases, the diagnosis had been missed at least twice on succeeding X-rays of the patient in question. Most often, superimposed structures are responsible for having missed lesions on the chest X-ray; this was the case in 71% of the patients in whom a lesion was missed. The intra- and inter-observer variation in the detection of small tumours on the chest X-ray are quite large (kappa: 0.38 and 0.48, respectively). Providing clinical information or previous chest X-rays for purposes of comparison does not improve the observer performance. Separate evaluation by two assessors ('double reading') also does not improve the results significantly. Simultaneous evaluation ('dual reading') improves the sensitivity slightly (from 28 to 37%), but has hardly any effect on the specificity (from 93 to 92%), thus improving the results somewhat. The results with computed tomography are much better (high sensitivity but low specificity). A CT-scan of the chest seems indicated in case of a suspicion of lung cancer and/or when there is a (slight) suspicion of lung cancer on the basis of the chest X-ray.

Humans↗