Katherine A. Lathrop

Bone-Seeking Radionuclides: An In Vivo Study of Factors Affecting Skeletal Uptake

The factors governing the skeletal uptake of bone-seeking radionuclides in vivo have not been clearly defined. In this study, the effects of alteration in blood flow (thermal-induced) and alteration in osteogenesis (ricket-induced) on the skeletal uptake of these agents in rats were investigated. In vivo quantitative data were corroborated by the use of autoradiographic and well-counting techniques. Results indicate that the short-term uptake of commonly used bone-scanning agents is closely correlated with blood flow and is largely independent of the rate of osteogenesis.

TECHNETIUM 99M AS A SCANNING AGENT.

INTEREST has increased over the past few years in the use of technetium 99m as a radioactive tracer material for organ and tumor localization studies (1). Initially, attention was focused on this nuclide because of its favorable physical properties for biological applications (2). Subsequent chemical and physiological studies have revealed remarkably versatile characteristics which may make Tc99m the radioisotope of choice in a variety of clinical applications (3–13). This report summarizes the progress made in our laboratory during the past four years in investigating this isotope. Chemically technetium belongs in group VII-A along with manganese and rhenium, the resemblance to the latter being particularly close. The physiologic behavior of technetium compounds has not been extensively studied except for the pertechnetate. This rather stable ion resembles iodide very closely in its initial distribution in the body (14). Like iodide it is selectively concentrated in the thyroid, salivary glands, and stom...

Clinical myocardial imaging with nitrogen-13 ammonia

Myocardial infarcts may be clearly imaged using intravenous nitrogen-13 as carrier-free ammonia in doses of 10–30 mCi. This positron emitter is well imaged with the Nuclear Chicago HP Anger Camera with heavy collimation. The rapid blood disappearance of the agent gives good image contrast, and the short half-life and high isotope dosage give high-count density images with little radiation absorbed dose (5 mrad∕mCi total body).

Accumulation of indium-111-labeled human low density lipoprotein in the rabbit aorta: Implications for nuclear imaging of vascular lesions.

Nuclear imaging of atheromata must distinguish lesions from both blood pool and normal arterial tissue. We have examined spatial and temporal variations of indium-111-labeled human low density lipoprotein (LDL) accumulation in rabbit aortas. LDL-derived In-111 activity was time-independent in lesion-resistant regions of aortas from normal and hypercholesterolemic animals (mean 2.9 × 10(-6) percent injected activity per milligram tissue [%IA/mg]) and in lesion-prone regions of normal aortas (mean 7.1 × 10(-6) %IA/mg). In contrast, activity in sudanophilic lesions of hypercholesterolemic rabbit aortas reached a peak of 31 × 10(-6) %IA/mg at 92 hours postinjection. The mean ratio between activity in lesions versus lesion-resistant regions described a broad convex curve with minima of 4:1 at 14 hours and 136 hours and a peak of 14:1 measured at 72 hours postinjection. The mean ratio between In-111 in lesions and blood followed a sigmoid curve, rising exponentially from 1:25 at 14 hours to 1:3 by 72 hours postinjection. We conclude that optimal signal-to-noise ratios for monitoring atheroma-associated LDL-derived radioactivity occur late, not before about 3 days postinjection. Therefore, LDL labeled with In-111 or even longer-lived radionuclides holds the greatest promise for effective clinical nuclear imaging of atherosclerosis.

Multiparameter extrapolation of biodistribution data between species

Values of an inaccessible biological parameter in man may be predicted from values measured in animals by correlating with a parameter accessible in both species, such as body weight, energy production, excretion rate, etc. Predicting toxic effects, from environmental chemicals, of therapeutic doses for drug administration and of radiation absorbed dose from medical and environmental radioactivity depends on the rationalization of relationships between concentration and time when scaling to humans from animal data. For example, the retention of 99mTc, injected intravenously as pertechnetate, reaches 10% in the mouse at about 1 d, but this level occurs in humans at about 7 d. Making a simultaneous transformation between two species for the concentration and time variables by using a method of least-squares fitting, we have derived a series of transformation factors for several species. When correlated with a biological parameter such as body weight, these factors can be used to yield predicted values that are in good agreement with measured values. This system may be used with any related variables, making it useful for predicting other types of biological data.