Comparison of bone formation rates measured by radiocalcium kinetics and double-tetracycline labeling in maintenance dialysis patients.

We report 23 prospective studies on 18 maintenance dialysis patients in whom we measured skeletal mineralization rate (m) using 47Ca, analyzed by the expanding pool model, and compared it with the histologic bone formation rate (bfr), volume referent, estimated on tetracycline-labeled iliac crest bone. The patients showed a spectrum of bone disease types including adynamic bone, aluminum-related osteomalacia, and various degrees of secondary hyperparathyroidism. The mean width between double labels, on which mineral apposition rate depended, was estimated using a simple formula relating area to perimeter for each feature enclosed by the labels. Values for m ranged from 0 to 155 mmol calcium per day and for bfr from 0 to 124% per year. There was close correlation between m and bfr (r = 0.976), serum alkaline phosphatase (r = 0.968), and serum immunological parathyroid hormone (iPTH) (r = 0.868). When the volumetric bfr was converted to mass units and applied to the whole skeleton, using literature values for mineral density and cortical and trabecular mass, there was close agreement between the histologic and isotopic estimates of m (r = 0.959). The results validate the two methods and suggest they are interchangeable. However, use of a rigorous method to determine bfr appears to be essential.

The computational restoration of autoradiographic images.

A double integral formula is derived for the distortion in an autoradiographic image due to electron "cross-fire", and a deconvolution procedure for image restoration using a fast Fourier transform algorithm is developed. The technique is applied to a simulated autoradiograph of a uniform disc source and is found to give excellent results. Further image enhancement is obtained from the use of a spatially moving average smoothing process.

Iron uptake by human reticulocytes at physiologic and sub-physiologic concentrations of iron transferrin: the effect of interaction with aluminum transferrin.

We have studied the interaction, in vitro, between diferric transferrin (FeTr), aluminum transferrin (AlTr), and human reticulocytes harvested from human placental blood. In particular, we aimed to determine the extent to which the kinetics of AlTr and FeTr differed. Using transferrin labeled with either 59Fe or 125I, the association of radiotracer with reticulocytes, as a function both of time and of transferrin concentration, was examined. Under the conditions of the experiments, the data are consistent with a mechanism involving at least three processes. Two early processes acting in parallel behave as a high-affinity saturable receptor and a low-affinity non-saturable receptor, neither of which distinguish between AlTr and FeTr. In a subsequent process, AlTr and FeTr exhibit different kinetics. This third process may be saturated by FeTr but not by AlTr. Interpreted in terms of a current conventional view of metallo-transferrin uptake, we conjecture that the early parallel processes involve cell surface phenomena including classical transferrin-receptor binding, and that the subsequent process represents events, possibly intracellular, involved in metallo-transferrin dissociation or further iron transport. The extent to which AlTr influences the interaction of FeTr with reticulocytes offers insight into both the normal physiology of iron uptake and the potential for toxicity by aluminum.

Magnetic resonance imaging using a ribbonator: hand and wrist.

A modified version of a single-turn solenoid with rectangular symmetry, which we call a ribbonator, provides excellent magnetic resonance images of the hand and wrist when used as both the transmitter and the receiver in a 1.5-T clinical imaging system. The very high RF efficiency provides excellent signal-to-noise and anatomical resolution. Design equations and RF properties of the resonator are discussed.

Transport dynamics of the hepato-biliary system: a mathematical model allied to Tc 99m IDA scintigraphy.

A generalised mathematical model of hepatic biliary tracer flows is formulated in terms of physiologically identifiable transport parameters. From a particular solution derived from this, the system response to intravenous administration of Tc99m IDA biliary tracer is predicted. Minimisation procedures applied to this solution combined with experimental scintigraphic observations yield estimates for the physiological parameters pertaining to a number of patient studies. Some hepatic conditions where quantitative indicators may contribute to clinical diagnosis are discussed.