PubMed Health⌕ Search

Biomedical subjects

U Feldman

Publications and source records attributed to U Feldman.

At least 19 recordsLinked to original sources
PubMed2005

Experimental benchmark for an improved simulation of absolute soft-x-ray emission from polystyrene targets irradiated with the Nike laser.

Absolutely calibrated, time-resolved spectral intensity measurements of soft-x-ray emission (hnu approximately 0.1-1.0 keV) from laser-irradiated polystyrene targets are compared to radiation-hydrodynamic simulations that include our new postprocessor, Virtual Spectro. This new capability allows a unified, detailed treatment of atomic physics and radiative transfer in nonlocal thermodynamic equilibrium conditions for simple spectra from low-Z materials as well as complex spectra from high-Z materials. The excellent agreement (within a factor of approximately 1.5) demonstrates the powerful predictive capability of the codes for the complex conditions in the ablating plasma. A comparison to data with high spectral resolution (E/deltaE approximately 1000) emphasizes the importance of including radiation coupling in the quantitative simulation of emission spectra.

Journal Article↗
PubMed2001

Efficient multi-keV underdense laser-produced plasma radiators.

Novel, efficient x-ray sources have been created by supersonically heating a large volume of Xe gas. A laser-induced bleaching wave quickly ionizes the high- Z gas, and the resulting plasma emits x rays. This method significantly improves the production of hard x rays because less energy is lost to kinetic energy and sub-keV x rays. The conversion efficiency of laser energy into L-shell radiation between 4-7 keV is measured at approximately 10%, an order of magnitude higher than efficiencies measured from solid disk targets. This higher flux enables material testing and backlighting in new regimes and scales well to future high-powered lasers.

Journal Article↗
PubMed2000

Perceived features reported as nodules: interpretation of spiral chest CT scans.

RATIONALE AND OBJECTIVES: The purpose of this study was to evaluate nontarget locations identified in a study of lung nodule detection with spiral computed tomographic (CT) scans that compared cine and film presentations. MATERIALS AND METHODS: In a previous study of lung nodule detection, eight observers were asked to identify 10 nodule locations in each of five CT scans containing eight simulated nodules. In the current study, each nontarget location that was reported more than once in the previous study was inspected with a stack-mode display in both cine and static modes. The nontarget locations were evaluated for probable identity, shape, and distance from the peripheral lung surface. RESULTS: Fifty-two nontarget locations included clinically undetected pulmonary nodules (n = 12), lymph nodes (n = 2), unclassifiable structures (n = 2), pleural scars (n = 8), and vascular structures (n = 28). Five nontarget locations contained vessels with complex courses apparent only with cine mode. As a group, nontarget locations were significantly closer to the periphery than would be expected by chance (for all locations, P < .0001; for locations not touching the pleural surface, P = .013). CONCLUSION: The lower reporting threshold caused by the observer instructions to find 10 targets resulted in increased reporting of structure with a nodular appearance. The locations of these reports in the lung periphery can be attributed to the relationship between frequent disease and a nearly featureless background in the lung periphery.

Adult↗
PubMed1998

Influence of CT image size and format on accuracy of lung nodule detection.

PURPOSE: To evaluate the effect of reducing image size on observers' ability to detect lung nodules on computed tomographic (CT) scans. MATERIALS AND METHODS: Stimuli were 80 single sections from 13 normal chest CT studies. On half of the images, 3-5-mm-diameter nodules were superimposed electronically at random locations. Four observers viewed images in six formats and sizes that ranged from 6 on 1 (133 x 133 mm) to 80 on 1 (40 x 40 mm). The images were viewed at a fixed distance of 55 cm and at an unrestricted, variable distance. RESULTS: With the fixed viewing distance, nodule detection decreased with smaller image sizes. The area under the receiver operating characteristic curve (Az) decreased from 0.857 for the 6-on-1 format to 0.671 for the 80-on-1 format (P = .0001). With a variable viewing distance, Az decreased from 0.884 to 0.834 across all formats (difference not statistically significant). However, there was a significant drop in performance with the smallest images (P < .05). Overall, Az for the fixed and variable viewing distances was significantly different (P < .001). CONCLUSION: Reducing image size leads to decreased lung nodule detection on CT scans viewed at a fixed distance; however, the observer can compensate for the smaller image by adjusting the viewing distance.

Humans↗
PubMed1997

Influence of visual distractors on detectability of liver nodules on contrast-enhanced spiral computed tomography scans.

RATIONALE AND OBJECTIVES: The authors evaluated the ability of observers to identify simulated nodules placed electronically on normal contrast material-enhanced computed tomography (CT) scans of the liver to assess the effect of nodule size and polarity on detection and localization. METHODS: Seven readers evaluated two sets of CT scans that contained 80 stimuli each. The simulated nodules were either darker or brighter than the contrast-enhanced liver and were 5.6-8.0 mm in diameter. Readers were asked to find the most suspicious-looking nodule on each section and rate the likelihood that the chosen location actually contained a nodule. RESULTS: The fraction of nodules found by each observer was substantially greater for dark nodules than for bright ones (0.679 +/- 0.03 vs 0.345 +/- 0.045, respectively [mean +/- standard error]). This difference was consistent for all nodule sizes. Additional analyses (including receiver operating characteristic curves of conditional responses) suggested that the presence of bright blood vessels distracted the readers and decreased their ability to find bright nodules. CONCLUSION: Normal vascular structures on contrast-enhanced CT scans of the liver impair an observer's ability to detect bright liver nodules.

Humans↗
PubMed1995

Spiral CT of the chest: comparison of cine and film-based viewing.

PURPOSE: To determine radiologists' ability to find lung nodules on spiral computed tomographic (CT) scans of the chest with both rapid sequential (cine) and conventional film-based viewing. MATERIALS AND METHODS: Eight radiologists searched for lung nodules on spiral CT images (10-mm collimation, 10 mm/sec table speed) presented in two formats. Cine viewing was performed at a computer work-station; sections were viewed in 2-mm increments at frame rates up to 10 frames per second. Film-based viewing of images from a laser printer was performed with a lightbox; sections were viewed at 4-mm increments. Eight 3-5-mm-diameter simulated nodules were superimposed on each of five normal CT scans. RESULTS: Radiologists found a higher fraction of nodules with the cine presentation than with film (mean, 0.69 +/- 0.02 [standard error] versus 0.58 +/- 0.03, respectively [P = .006]). Diameter thresholds for nodule detection (50% correctly localized) were 3.3 and 3.5 mm, respectively. CONCLUSION: Cine viewing of spiral CT images of the chest improved radiologists' ability to detect nodules.

Humans↗