James Hanson

Performance evaluation of a dual-energy X-ray bone densitometer

SummaryWe tested a dual-energy bone densitometer (LUNAR DPX) that uses a stable x-ray generator and a K-edge filter to achieve the two energy levels. A conventional scintillation detector in pulse-counting mode was used together with a gain stabilizer. The densitometer normally performs spine and femur scans in about 6 minutes and 3 minutes, respectively, with adequate spatial resolution (1.2×1.2mm). Total body scans take either 10 minutes or 20 minutes. The long-term (6 months, n=195) precision of repeat measurement on an 18-cm thick spine phantom was 0.6% at the medium speed. Precision errorin vivo was about 0.6, 0.9 and 1.5% for spine scans (L2-L4) at slow, medium and fast speeds, while the error was 1.2 and 1.5 to 2.0%, respectively, for femur scans at slow and medium speed. The precision of total body bone density was 0.5%in vitro andin vivo. The response to increasing amounts of calcium hydroxyapatite was linear (r=0.99). The densitometer accurately indicated (within 1%) the actual amount of hydroxyapatite after correction for physiological amounts of marrow fat. The measured area corresponded exactly (within 0.5%) to that of known annuli and to the radiographic area of spine phantoms. There was no significant effect of tissue thickness on mass, area, or areal density (BMD) between 10 and 24cm of water. The BMD values for both spine and femurin vivo correlated highly (r=0.98, SEE=.03 g/cm2) with those obtained using conventional153Gd DPA. Similarly, total body BMD correlated highly (r=0.96, SEE=.02g/cm2) with DPA results.

Antineuronal antibodies in patients having myasthenia gravis

SUMMARYThe gamma globulin fraction from the sera of normal individuals and from patients with myasthenia gravis, autoimmune thyroiditis, amyotrophic lateral sclerosis, and multiple sclerosis were labeled with fluorescein isothiocyanate. When sections of various organs, including nervous tissue, testis, kidney, liver, spleen, ovary, and muscle, were reacted with the fluorescein-labeled globulin obtained from patients with myasthenia gravis, an intense fluorescence was observed only in the nuclei of neurons and spermatogonia. This reaction was seen when tissue from various species, including man, was used. The labeled globulins obtained from normal individuals or from patients with the other disorders did not react in this manner with nervous tissue or testicular sections. When spinal ganglia from young animals were reacted with the fluorescein-labeled globulins from myasthenic patients, the resultant pattern of fluorescence was markedly different from that seen with tissue from mature animals. Thymectomy of two of the patients resulted in loss of the neuronal and spermatogonial reactivity of the labeled globulins. The relationship of these observations to the etiology of this disease is discussed.

Dynamics of

A bstractIn this note we consider N

= 4 supersymmetric field theories in 2 + 1 dimensions and their gravity dual

\mathcal{N}

Dual-energy X-ray absorptiometry for total-body and regional bone-mineral and soft tissue composition.

= 4 SYM theories in 2 + 1 dimensions with gauge group U(N ) × U(M ) and k hypermultiplets charged under the U(N ). When k > 2(N − M ), the theory flows to a superconformal fixed point in the IR. Theories with k < 2(N − M ), on the other hand, flows to strong coupling. We explore these theories from the perspective of gravity dual. We find that the gravity duals of theories with k < (N − M ) contain enhancons even in situations where repulson singularities are absent. We argue that supergravity description is unreliable in the region near these enhancon points. Instead, we show how to construct reliable sugra duals to particular points on the Coulomb branch where the enhancon is screened. We explore how these singularities reappear as one moves around in Coulomb branch and comment on possible field theory interpretation of this phenomenon. In analyzing gauge/gravity duality for these models, we encountered one unexpected surprise, that the condition for the supergravity solution to be reliable and supersymmetric is somewhat weaker than the expectation from field theory. We also discuss similar issues for theories with k = 0.

Standardization of Spine BMD Measurements

Heparin has been reported to decrease wound edema as well as improve the clearance of excess fluid after thermal injury. No quantitative data on burn edema are available to support these statements. We studied the effect of heparin in therapeutic doses on edema formation and resorption in the sheep hind limb after deep second (85°C)- or third (95°C)-degree burns. Heparin was given as a continuous infusion for 24 hr to increase clotting time 2.5-fold. We used dichromatic absorptiometry, a noninvasive, sensitive method for measuring tissue fluid, to quantitate edema. We found that heparin did not decrease the quantity of edema produced after a second-degree burn or increase the rate of resorption. In a variable third-degree burn, heparin treatment resulted in a significant increase in tissue edema (P < 0.005). Clearance of edema was markedly decreased after a third-degree burn as compared to second degree. Heparin did not improve this process.