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Three hundred and sixteen patients with solitary or dominant thyroid nodules were imaged both with technetium-99m- (99mTc) pertechnetate and iodine-123 (123I). The images were preferred, but differences were small and in 27%-58% of the cases there was no difference in quality between the two radionuclides. Discrepancies between 99mTc and 123I images were found in 5%-8% of cases, twice as often in multinodular goiters as in single nodules. Cytologic/histologic examination was performed on all nodules but no correlation was found between the pathology and the type of discrepancy. Twelve carcinomas were found (4%) but none in nodules showing a discrepancy. There was great variation among the observers about the preference for radionuclides and about the existence or type of discrepancies. The slightly better overall quality of 123I scans is probably not of diagnostic significance and does not justify the routine use of 123I instead of 99mTc. Routine reimaging of 99mTc hot nodules with radioiodine for cancer detection does not appear to be necessary.

Newly synthesized Tc-99m dichlorobis(1,2-dimethylphosphino)ethane (DMPE) was investigated as a myocardial imaging agent with respect to its kinetics (dependent on both time and regional coronary blood flow), its percent organ uptake, and its imaging characteristics in the anesthetized dog. Most of these data are compared with those of Tl-201. Blood clearance of the two agents is essentially the same. Compared with Tl-201, Tc-99m DMPE shows faster overall kinetics, higher heart-to-lung ratio, equally good correlation with a wide range of regional blood flows, and higher liver uptake. At the time of peak myocardial uptake, the mean heart uptake of Tl-201 is 4.3%, compared with 2.9% for Tc-99m DMPE, yet only 0.9% uptake of Tc-99m DMPE is found in the lung as compared with 3.3% for Tl-201. These differences result in a heart-to-lung ratio of 2:1 for Tc-99m DMPE and 1:1 for Tl-201, based on the data obtained from the time-activity curve. The quantitative findings are supported by the superior quality of Tc-99m DMPE images of both normal and infarcted dog heart. The high hepatic uptake of Tc-99m DMPE is not a serious problem if images are obtained within 5-60 min after dose. These basic kinetic studies suggest that Tc-99m DMPE is a promising myocardial imaging agent.

The cost-effectiveness of pulmonary imaging (lung scan) on the management of 2,023 patients was studied. Prior and postscan probabilities of pulmonary embolism (PE) were obtained from referring physicians. After the scan, anticoagulant therapy (ACT) was appropriately changed in 20% of the patients and confirmed in 67%. The incremental cost of scanning was $124 per patient when the prior probability was 0.01-9.99%, dropping to $38 when the probability was 10-25%. Hospitalization and ACT cost was reduced when the prior probability was 25.01-99.99%. The greatest benefit in lives saved was when the prior probability was 25-74.99%; 1.5% of this probability group would survive as a result of the change in management attributable to the scan, at a cost of $117 per life saved. The benefit:risk ratio, as measured by lives saved compared to estimates of lives lost due to radiation exposure, was of the order of 6,000:1.

Etidronate and pyrophosphate, labeled with Tc-95m and Tc-99m, were studied in experimentally infarcted mongrel dogs. A distribution study was conducted 2 hr after simultaneous administration of both agents in two groups of dogs. In one group, the injection was made 15 min after release of a 2-hr coronary arterial ligation. Another group was injected 48 hr after release of the ligation. The uptakes for each radiopharmaceutical and the ratio of uptakes for each sample were computed. The data show pyrophosphate to be a superior agent for the imaging of acute myocardial infarcts because of the higher uptake by infarcted myocardium and the greater contrast between infarcted myocardium and neighboring organs.

The diagnosis of intrahepatic aneurysm was suspected following radioisotope scintigraphic studies. A patient developed abdominal pain following blunt abdominal trauma. The scintigrams of the liver revealed a large intrahepatic defect and separation between lung and liver. Angiogram revealed a large false aneurysm of the right hepatic artery.

Detection of breast disease at an early stage was evaluated with 131CsCl. The tissue distribution study showed that malignant tumors could be distinguished from both benign and normal tissue by the degree of 131Cs concentration. However, the external counting method was not sensitive enough to warrant general application to patients with a suspected malignant tumor of the breast. False-positive breast study findings using radionuclides, such as 131CsCl, require close follow-up study in view of possible malignant changes in benign disease of the breast.

An information-theoretic pattern recognition method was used to construct descriptive models of data related to 1,674 radioisotope lung scan referrals for the purpose of assessing lung scan influence on diagnosis and management of pulmonary embolism. It was observed that, relative to other clinical information available prior to the scan, the lung scan significantly improved the ability of the models to predict diagnostic and management outcomes, implying that the lung scan has significant influence on these clinical decisions.

129CsCl was investigated as an agent for imaging tumors of the lung, and based on the results of 56 patients studied, it has proved to be highly sensitive in detecting primary malignant tumors of the lung. The differentiation between pulmonary malignant lesions and tuberculosis appears to be feasible. However, false-positive images in patients with benign conditions are inevitable.

This paper describes a Society of Nuclear Medicine sponsored study of 2,023 patients which compares two methods, logistic regression (LR) and entropy minimax pattern detection (EMPD), to evaluate efficacy. Lung scans, used in determining or excluding a diagnosis of pulmonary embolism (PE), were utilized to create the data set. The LR analysis, presented here, shows that lung scan findings have significant influence on the referring physician's diagnostic thinking. Models were developed for the probability of a signout diagnosis of PE, and equal patient groups tested the validity of these regression equations. Individual models developed on each patient group yielded similar results. This analysis shows that the lung scan results affect the therapeutic management of the patients in a beneficial direction. A comparison of the sensitivity, specificity, and predictive values of EMPD and LR was done. EMPD predicts a signout diagnosis on only 41% of cases before lung scan and 71% after lung scan; LR provides a prediction of the signout diagnosis on 100% of cases. An advantage of EMPD is that it does not require prior probability estimates. However, LR uses this estimate, thus incorporating intuitive knowledge not evaluated by EMPD.

After intravenous administration of Tc-99m DMPE the flow-dependent kinetics were studied in dogs during induced ischemia and during induced maximal reactive hyperemia. A control group was also studied. Mean time-activity curves obtained from the myocardial wall were compared within the same intervention group and also with other groups. During reactive hyperemia, there was a rapid and absolute increase in uptake followed by a rapid washout, whereas during ischemia there was a slow and decreased uptake followed by a slow washout. The magnitude of Tc-99m DMPE uptake during reactive hyperemia was slightly less than that of Tl-201, but the decreased uptake with ischemia was about equal for the two agents. Following maximal uptake in the myocardium the effective half-life of Tc-99m DMPE was one-third to one-fourth that of Tl-201. The similar kinetics of Tc-99m DMPE compared to Tl-201 suggests its usefulness in the evaluation of ischemic heart disease.

A Gamut is defined as a complete list of anything. As utilized here, it indicates a complete list of the possible causes of a particular scintigram finding. The procedure for developing a Gamut is discussed, ant its use as a tool for instructing residents in nuclear medicine is described. Sample Gamuts are presented and the Gamut approach to scintigram differential diagnosis is described.

Individual observers interpreted images in order to assess their accuracy and sources of error. Seventy-six liver images were presented to nine readers for interpretation. Readers of differing experience participated in the study: four radiology residents, three fellows in nuclear medicine, and two full-time nuclear medicine physicians. A higher incidence of false-positive reading was more common in inexperienced observers (11-50%) and the most correct readings were obtained by staff physicians (88% overall percentage accuracy). Heterogeneity in radionuclide uptake was the most frequently ill-defined nature was the most common false-positive finding in normal cases. Early stages of cirrhosis, mild hepatitis, and rare diseases such as hepatic sarcoidosis were difficult to detect. Skill of interpretation improved with experience, especially in judging heterogeneity of an ill-defined nature, and the rate of accurate readings was proportional to the level of training of the observer.