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Biomedical subjects

C E Ravin

Publications and source records attributed to C E Ravin.

139 records · Page 8Linked to original sources
PubMedDate not supplied

Elevation of pulmonary artery pressure as a sign of pulmonary barotrauma (pneumothorax).

Pneumothorax occurs in approximately 25% of patients maintained on high levels of positive end-expiratory pressure. In several cases at our Institution, a sudden and rapid elevation in pulmonary artery pressure (PAP) monitored by use of the Swan-Ganz catheter accompanied the development of a pneumothorax. In the three cases described, the change in PAP was observed before a pneumothorax became otherwise clinically evident. Two of the three patients had marked restrictive lung disease associated with the adult respiratory distress syndrome and the third patient had large bilateral pleural effusions. It is postulated that the rise in PAP was related to a sudden decrease in the size of an already compromised pulmonary arterial vascular bed produced by hypoxic vasoconstriction and mechanical compression secondary to the pneumothorax. In the ICU, elevation of PAP may be a useful and early indicator of pulmonary barotrauma.

Adult↗
PubMedDate not supplied

Physical principles governing the interrelationships of pressure, flow and volume in collapsible tubes.

Basic principles of fluid mechanics may be used to analyze the relationships of flow, pressure and cross-sectional area of any collapsible tube, including pulmonary blood vessels. The cross-sectional area of a collapsible tube is a direct function of transmural pressure. Alterations in pressure inside the tube may result from changes in fluid velocity, downstream constriction in the tube, or direct increase in internal pressure, as with a manometer. This paper reviews the basic equations applicable to flow in collapsible tubes and illustrates the principles of such flow with a physical model. Depending upon the circumstances, changes in size of the tube may or may not reflect changes in flow or changes in fluid velocity.

Biophysical Phenomena↗
PubMedDate not supplied

Accuracy of the chest radiograph in diagnosis of pulmonary embolism.

In an effort to determine the sensitivity and specificity of the chest roentgenogram for the diagnosis of pulmonary embolism, roentgenograms of 152 patients who were all suspected of having pulmonary embolism were randomized and presented to nine interpreters. One hundred eight patients in the series were proven to have pulmonary embolism on the basis of a positive pulmonary angiogram. Forty-four patients were assumed not to have embolism on the basis of either a normal perfusion isotope scan or a pulmonary angiogram which did not show embolism. The interpreters were requested to indicate whether pulmonary embolism was present or absent, or whether they could not tell from the roentgenogram. Readers had no prior knowledge of the actual disease state. The average true-positive ratio (sensitivity) was 0.33, with a range of 0.52 to 0.88. The average true-negative ratio (specificity) was 0.59, with a range of 0.31 to 0.80. The false-positive and false-negative ratios were respectively, 0.21 (range 0.05 to 0.39) and 0.41 (range 0.15 to 0.70). A predictive index, reflecting the overall accuracy of diagnosis, was calculated for the entire group and was 0.40, with a range of 0.17 to 0.57. There appeared to be no correlation between training or experience and accuracy of performance in this study.

False Negative Reactions↗
PubMedDate not supplied

Performance of high-resolution monitors for digital chest imaging.

High-resolution cathode-ray tubes (CRT's) are currently the most viable soft-copy display for digital radiography. We present here methods for measuring large-area contrast ratio and detail contrast ratio. A two-dimensional charge coupled device (ccd) array signal-averaged with a video frame buffer permits linear microradiometric measure of individual beam lines. Results from three different 1000-line monitors demonstrate the shift variance of resolution. The detail contrast ratio (or modulation depth) was found to vary from 100% to less than 10% across the face of one CRT. Dynamic focus in both the horizontal and vertical deflection circuitry proved effective in reducing this shift variance. Comparisons of three phosphors demonstrate the utility of long persistence phosphors (P164) for static display in producing brighter images with less flicker. Recommendations for CRT design and selection for high-resolution digital radiography are included.

Computer Systems↗
PubMedDate not supplied

Quantitative radiographic imaging using a photostimulable phosphor system.

We have evaluated a photostimulable phosphor x-ray imaging system [Philips Computed Radiography (PCR) system] for use in quantification of x-ray exposure in diagnostic radiography. An exponential function was fitted to data yielding quantitative x-ray exposure values as a function of digital pixel values. We investigated several factors that affect the accuracy of exposure measurement using the PCR including repeatability, background noise as a function of time delay between plate erasure and use, sensitivity variation between different plates, nonuniformity of sensitivity within a plate, decay of the latent image between time of exposure and readout (observed as a change in sensitivity), and the accuracy with which the (exponential) calibration function yields exposure values as a function of digital pixel values. The calibration was performed over the exposure range from 5.1 X 10(-9) to 2.0 X 10(-5) C/kg (0.02-75 mR). The accuracy of exposure measurements made with a single imaging plate is between 1.6% and 4.2%. If measurements from several plates are involved, the uncertainty in the final measurement will be between 5% and 5.9%.

Evaluation Studies as Topic↗
PubMedDate not supplied

Quantitative scatter measurement in digital radiography using a photostimulable phosphor imaging system.

X-ray scatter fractions measured with two detectors are compared: a photostimulable phosphor system (PSP) and a conventional film-screen technique. For both detection methods, a beam-stop technique was used to estimate the scatter fraction in polystyrene phantoms. These scatter fraction measurements are compared to previously reported film-based measurements. Scatter fractions obtained with the PSP were in good agreement both with measurements using film as well as with most previously reported measurements. For the PSP measurements, repeatability was better than 1%. It was found that the PSP provides a precise x-ray detector for quantitative scatter measurement in digital radiography.

Luminescent Measurements↗
PubMedDate not supplied

An artificial neural network for estimating scatter exposures in portable chest radiography.

An adaptive linear element (Adaline) was developed to estimate the two-dimensional scatter exposure distribution in digital portable chest radiographs (DPCXR). DPCXRs and quantitative scatter exposure measurements at 64 locations throughout the chest were acquired for ten radiographically normal patients. The Adaline is an artificial neural network which has only a single node and linear thresholding. The Adaline was trained using DPCXR-scatter measurement pairs from five patients. The spatially invariant network would take a portion of the image as its input and estimate the scatter content as output. The trained network was applied to the other five images, and errors were evaluated between estimated and measured scatter values. Performance was compared against a convolution scatter estimation algorithm. The network was evaluated as a function of network size, initial values, and duration of training. Network performance was evaluated qualitatively by the correlation of network weights to physical models, and quantitatively by training and evaluation errors. Using DPCXRs as input, the network learned to describe known scatter exposures accurately (7% error) and estimate scatter in new images (< 8% error) slightly better than convolution methods. Regardless of size and initial shape, all networks adapted into radial exponentials with magnitude of 0.75, perhaps implying an ideal point spread function and average scatter fraction, respectively. To implement scatter compensation, the two-dimensional scatter distribution estimated by the neural network is subtracted from the original DPCXR.

Algorithms↗
PubMedDate not supplied

The three syndromes of fat embolism: pulmonary manifestations.

The clinical course and radiographs of 30 patients with fat embolism syndrome were reviewed. In all cases the classic triad of neurologic dysfunction, respiratory insufficiency, and petechiae were present. Three responses to embolized fat were noted. The hyperacute response was seen in two patients with paradoxical embolization of fat to the systemic circulation. A "classic response" was noted in 18 patients with transient respiratory compromise and variable radiographic findings. The two deaths in the group responding in the classical manner were attributed to massive pulmonary emboli. The third response, noted in ten patients, consisted of a chest radiograph compatible with pulmonary edema in the clinical setting of the adult respiratory distress syndrome. In this group the degree of respiratory dysfunction and pulmonary damage correlated with the development of disseminated intravascular coagulation. Pathologic correlations are presented and the mechanisms by which embolic fat produces tissue damage are discussed.

Adolescent↗