Leonard Shabason

Side effects of xenon inhalation.

Short- and long-term side effects during and after inhalation of premixed xenon oxygen (28-47%) from 12 studies are reported. While all but one subject tolerated xenon inhalation without ill effects, that individual did experience unpleasantly severe dysesthesias and a brief period of unresponsiveness. We believe that further human studies with xenon inhalation should be conducted to explore possible early indicators for reduced tolerance of xenon by certain individuals.

Regional pulmonary ventilation measurements by xenon enhanced dynamic computed tomography: an update.

New developments in computed tomographic technology permit rapid, serial images that may yield information concerning tracer kinetics through a large tissue volume. One possible application of these developments is the derivation of local lung ventilation by observing the temporal changes of stable xenon concentrations. Preliminary results from six multilevel ventilation studies in dogs demonstrate that the lung may be repeatedly imaged during reproducible phases of respiration even when interscan table incrementation is employed to survey a number of tissue segments and breathing is permitted between scans. In addition, subanesthetic xenon concentrations provide adequate enhancement for possible quantification.

Mapping of human local pulmonary ventilation by xenon enhanced computed tomography.

Functional maps of local pulmonary ventilation are derived from serial computed tomographic images acquired prior to and during a short period of inhalation of subanesthetic xenon/oxygen gas mixtures. Preliminary results from human studies yield quantitative maps of local ventilation rates with excellent anatomic specificity demonstrating nonuniformities in the distribution of ventilation in normal and abnormal human lungs.

Efficiency of Ge(Li) and Si(Li) planar detectors in the 2–5 keV energy range☆

Abstract A simple experimental method is described for determining the average thickness of the dead layer of Ge(Li) and Si(Li) detectors, which is the main contributing factor to their drop in efficiency at very low photon energies.

Errors associated with single-scan determinations of regional cerebral blood flow by xenon enhanced CT.

Possible errors in the determination of xenon concentrations in arterial blood, and uncertainties in CT tissue enhancements during inhalation of xenon-oxygen mixtures, are used to assess errors in the determination of regional cerebral blood flow by the in vivo autoradiographic (single-scan) technique. The results of this study indicate that errors associated with the determination of xenon concentrations in arterial blood decrease rapidly as the time of scanning after the initiation of xenon inhalation is increased. Analysis of errors caused by statistical uncertainties in image enhancement indicate that time of scanning is optimal between 1.5 and 2.5 min for determination of fast flow, while errors in single-flow determinations gradually decrease as the time of scanning increases.

Helium depth profiles in thin metal foils

Abstract A technique is presented for measuring helium depth profiles in thin metal foils. The method gives submicron depth resolution and allows practical concentration measurements in the range of 1–10 atomic parts per million.

Measurement of Local Cerebral Blood Flow by Xenon-Enhanced Computerized Tomography Imaging: A Critique of an Error Assessment

A review of an error assessment of local cerebral blood flow values derived from xenon-enhanced computerized tomography imaging indicates that the authors have failed to consider the appropriate parameters, thereby yielding errors that are larger than the true errors.

Equilibrium charge distribution for small impact parameter O + Xe collisions☆

Abstract The charge distributions of oxygen ions with incoming charges 4 + –7 + scattered to 5° in a single collision with various gases have been studied. The measurements indicate that for the heavier gases an “equilibrium charge distribution” is obtained after a single small impact parameter collision.

Fiber Optically Coupled Diode Array Digital Radiography System

A new type of digital radiography system of very high contrast sensitivity and spatial resolution is described which is based on the use of six linear arrays of self-scanning diodes fiber-optically coupled to a phosphor screen. The high detail of the system results from the fact that 6144 discrete diodes, 1024 per array, scan a field of view of 6 inches wide. A contrast sensitivity five times greater than film is achieved due to the high dynamic range of the diodes combined with the scatter rejection associated with the slit geometry. The entrance radiation exposure per image is 100 mR but could be reduced well below that in the future. Initial clinical experience has demonstrated the advantage of being able to display a single image over a wide range of window levels and window widths at the same time having a high contrast sensitivity in both the dark and light areas of the image. The complete digital radiograph is taken in a second, however the motion unsharpness is held to a minimum by virtue of an effective exposure time of 8 milliseconds. Applications to digital chest radiography and digital intravenous subtraction angiography in over 30 patients have shown the clinical value of this new form of radiography.

PROGRESS IN CEREBROVASCULAR DISEASE: LOCAL CEREBRAL BLOOD FLOW BY XENON ENHANCED CT

A noninvasive technique for measuring local cerebral blood flow (LCBF) by xenon enhanced x-ray transmission computed tomography (CT) has been developed an reported quite extensively in recent years. In this method, nonradioactive xenon gas in inhaled and the temporal changes in radiographic enhancement produced by the inhalation are measured by sequential computed tomography. Time dependent xenon concentrations within various tissue segments in the brain are used to derive both local partition coefficient (lambda) and LCBF. An assessment of this method reveals that although it provides functional mapping of blood flow with excellent anatomic specificity, there are distinct limitations. The assumptions underlying this methodology are examined and problems associated with various potential applications of this technique are discussed.