Compton scatter densitometry with polychromatic sources.

The use of x-ray tubes as radiation sources for Compton scatter densitometry (CSD) is evaluated theoretically. Bias correction factors (bcf's) which correct for differential attenuation due to Compton shift and polychromaticity, and differential scattering cross section due to polychromaticity, are defined to facilitate comparison of monochromatic and x-ray tube CSD devices. Computer modeling indicates that a 100-kVp x-ray tube spectrum hardened with 0.64 mm of Pb filtration yields bcf's 0.008 to 0.34% higher than a 70-keV monochromatic source for various samples of nylon, and human muscle and bone. This difference is insignificant because multiple scatter errors are typically 1000% higher than errors corrected by bcf's. The high equivalent activities of x-ray tubes (10 to 80 TBq) and their small focal spots (1.0 to 2.0 mm) allow the long-standing CSD problems of marginal statistical precision, long counting times, and low spatial resolution to be overcome.

Simulation studies of dual-energy x-ray absorptiometry.

Computer simulations were performed to predict the performance characteristics of dual-energy x-ray absorptiometry. K-edge filter techniques were analyzed in detail and compared to 153Gd sources in terms of output intensity, precision, patient dose, image contrast, beam hardening, and marrow fat effects. Similar analyses were performed for two dual-kV techniques that have been reported in the literature. The simulations indicate that K-edge filter techniques, or a dual-kV technique combined with K-edge filtering, can provide performance capabilities that equal or exceed those achievable with 153Gd systems. A (70/140) dual-kV technique with conventional (Al or Cu) filtration also has advantages in terms of source output intensity, but is 2-3 X inferior to the K-edge techniques and 153Gd in terms of patient dose and beam-hardening effects.

Compton scatter with polychromatic sources for lung densitometry.

A mobile lung densitometer using conventional x-ray tubes, NaI detectors, and principles of two-source, two-detector Compton scattered densitometry, is described. The device is capable of one to two per second density measurements from a 45-cm3 volume with a precision of 5%. The expected in vivo accuracy (2%-3%) is determined by using an anthropomorphic phantom with replaceable lung inserts. The unintentional detection of multiple-scattered x rays results in a small density-dependent error. This error is predictable and relatively insensitive to differences in surrounding absorbers such as the chest wall. With this device, dynamic in vivo densitometry of the lung in the clinical laboratory and intensive care unit will be possible.

Pyruvate kinase deficiency and leg ulcers.

We report a family with a new pyruvate kinase (PK) variant in which leg ulcers have been present in four of the five affected homozygous family members, but not in any of the unaffected individuals. The propositus, an 18-yr-old boy, suffered from recurrent crises of hemolytic anemia and leg ulcers. A splenectomy was performed and the leg ulcer was treated un-successfully with a pinch graft. Studies ondialyzed hemolysates showed that the enzyme was kinetically abnorma, being almost entirely resistant to activation by fructose diphosphate. THE THERMOSTABILITY OF THE ENZYME WAS MODERATELY DECREASED, AND THE ELECTROPHORETIC MOBILITY WAS NORMAL. One may speculate that the development of leg ulcers in some kinships with PK deficiency may be related to variants of PK which exert unusual effects on the rheologic properties of the red cell in vivo.