We have developed a new model of short-term fluoride kinetics in humans and have solved the model on a digital computer using the SAAM-25 program. The solution accords well with available data. About ...60% of intravenously administered 18F fluoride is taken up by bone. Evaluation of the rate constants of tracer egress from blood indicates that about 17% of the cardiac output is distributed to the skeleton. When the model was perturbed to simulate changes in systemic or skeletal blood flow, we found that the system behaves in a nonlinear manner; even a five-fold increase in systemic or skeletal blood flow did not appreciably increase the amount of fluoride taken up by bone 1--2 hr later, the time when scans are usually made. A simulated increase in bone extraction rate, however, had a marked effect on bone-fluoride uptake. These findings suggest an important homeostatic role for bone in the regulation of blood calcium concentration and have considerable bearing on the interpretation of bone scans.
A case report of an 82-year-old woman with carcinoma of the gallbladder is presented. Technetium-99m DISIDA cholescintigraphy demonstrated nonvisualization of the gallbladder, with a large ...photon-deficient region corresponding to the gallbladder fossa, with medial displacement of the common bile duct. Carcinoma of the gallbladder has not been previously described as a cause of this scintigraphic pattern.
Using compartmental analysis techniques, we modeled the biodistribution of Tc-99m(Sn)methylene diphosphonate in humans on a computer, and by selectively perturbing appropriate rate constants, we ...simulated changes in contrast between bone and soft tissue in a number of systemic disorders. The model predicts low contrast in patients with moderate to marked edema, obesity, congestive heart failure or decreased cardiac output states and high contrast with as little as 25% increase in bone avidity for the tracer. In acute renal failure without fluid-volume imbalance, image contrast should be normal. The model predicts greater contrast shortly after injection in patients with increased cardiac output, skeletal blood flow, or bone avidity; images made at these times would be indistinguishable. These simulations are in keeping with reports in the literature of bone images and bone-to-soft tissue ratios in many of these conditions, suggesting that modeling studies could play an important role image interpretation.
First-harmonic Fourier analysis of a gated blood-pool study is based on the assumption that the cardiac chambers contract once per cardiac cycle. In atrial arrhythmias this condition may not exist ...for the atria. We recently studied a patient with atrial flutter and 2:1 atrioventricular conduction. There were predictable alterations in the first-harmonic Fourier phase and amplitude images. The observed changes from first-harmonic Fourier analysis were: (a) very low atrial amplitude values, and (b) absence of identifiable atrial regions on the phase image.
Uptake of thallium in a patient with sclerosing adenosis of the breast was detected. Although thallium has been reported to accumulate in primary carcinoma of the thyroid, lung, and liver, detection ...of a breast lesion on a thallium scan has not been previously reported.
We have evaluated a five-compartment model of 18Ffluoride kinetics in rats. The initial fluoride distribution was found to be similar to that of 77Brbromide, a known extracellular-fluid (ECF) tracer, ...in agreement with the hypothesis underlying the model, and the measured uptake rate in rat bones compared well with the digital computer solution. Simpler models did not give a better fit. In dead rats, fluoride movement was found within the skeleton, presumably from bone ECF to bone substance, although not as rapidly as predicted or found in the live animal. Evaluation of the rate constants permitted estimates to be made of cardiac output, skeletal blood flow, and bone ECF volume, all in accord with independent measurements. It is suggested that skeletal blood flow at rest is a constant fraction of body weight, and probably subserves a hematopoietic as well as a mineralization function.
Nineteen patients undergoing exercise thallium scanning had two separate redistribution 40 degree LAO acquisitions obtained; the gamma camera was repositioned between the views. Data were analyzed by ...generating 60-point circumferential profile curves for each of the 38 images and the variability of individual points and 18 degrees and 36 degrees segments was determined. Intraobserver variability, assessed by reanalyzing the scans one week later, was approximately 5.0%. The interobserver variability was of similar magnitude (approximately 6%). The total reimaging variability was, however, significantly larger (approximately 13%). It is concluded that quantitative image analysis is highly reproducible with low intra- and interobserver variabilities, but the act of repositioning and reimaging introduces significant additional variability. This may limit the ability of quantitative thallium scanning to document changes in the size of defects.
A prospective study was performed to determine the frequency with which defects on stress thallium images undergo rapid resolution. Analysis of paired views showed that 15% of the defects present in ...anterior views resolve in less than 30 minutes. This study documents the loss of sensitivity that can occur if imaging does not begin promptly after injection.
