Abnormal thyroid function profoundly alters calcium metabolism. In 1929, Aub, Bauer, Heath, and Ropes (1) demonstrated in patients on constant low calcium diets that urinary and fecal excretion of calcium and phosphorus is frequently increased in hyperthyroidism and lower than normal in myxedema. These changes could not be ascribed to elevation of metabolism per se (1) acidosis (2) or vitarmin D deficiency (3); they were observed even in the absence of the parathyroid glands (4, 5). In addition, roentgenographic evidence of skeletal demineralization has been described in patients with thyrotoxicosis (6).The conventional balance techniques which have been used in the study of calcium metabolism in thyroid disease measure only net effects: they do not measure the processes of deposition and resorption of calcium. An indication of the skeletal turnover of calcium, however, can be obtained from serial observations of the specific activity of radioactive calcium (Ca45) in blood and urine after intravenous injection (7,8).The present study was designed to define the alterations in calcium metabolism in thyroid disease in man by using Ca45 and the technique of isotope dilution. Observations have been made in euthyroid, hyperthyroid, and myxedematous subjects, and, for purposes of comparison, in additional euthyroid patients with Paget's disease and with hypoparathyroidism. MATERIALS AND METHODSAll patients (Table I) were on the metabolic ward and were ambulatory throughout the study. Diets, which were constant and of neutral ash, contained from 0.08 to 0.23 grams of calcium per day (Table II). In order to avoid tetany, the two hypoparathyroid subjects were given 0.31 and 0.57 grams, respecfively, of calcium in their diets per day. Fluid intake was maintained at 2,000 to 2,500 ml. per day. Complete collections of urine and stool were begun after six days on the fixed diet. A three-day control collection of urine and feces was obtained prior to the administration of Ca.The stock solution of Ca"Cl, 2 was acidified with concentrated HCI, added to 0.9 per cent NaCI solution to give a final concentration of approximately 0.5 j&c per ml.saline at a pH of 6, and autoclaved. Five to seven microcuries were injected from a calibrated syringe into an antecubital vein one hour before breakfast. Blood samples were obtained by venipuncture from the opposite arm at frequent intervals. Fractional urine collections were made for the first three days following injection, and daily thereafter. Stool collections were made TABLE I

The effect of positron range on the image-plane resolution of tomographic images is evaluated through calculations based on a model which employs beta-decay energy spectra and an empirical range formula. Predicted range distribution functions are compared with published measurements for three medically important positron emitters: (11 )C, (68)Ga, and (82)Rb. The effect of tomographic slice thickness on point-source annihilation distribution functions is also demonstrated. Line-spread functions are calculated using the model, for the above isotopes as well as for (18)F, (15)O, and (13)N. Image-plane resolution predictions are made for high-resolution positron cameras for various positron emitting isotopes with end-point energies up to 4 MeV.

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