[Pulmonary scintigraphy using the inhalation of monodispersed radioactive aerosols. Preliminary report]. / La centelleografía pulmonar mediante la inhalación de aerosoles radiactivos monodispersos. Informe preliminar.

This article describes a method for inhalatory lung scintigraphy (ILS) by the use of radioactive monodisperse aerosols, with particles smaller than 2 microns. We discuss the findings in normal subjects, in patients with pulmonary embolism (PE) or/and obstructive pulmonary disease (OPD), and in individuals with severe pulmonary hypertension. This procedure has several advantages over the use of radioactive gases, such as 133Xe and 81Krm: lower cost, easier to perform, several scintigraphic projections in one study, acquisition of perfusion and inhalatory images in a single session, and inhalatory and perfusion images with identical spatial resolution and similar data density. It is concluded that ILS with radioactive monodisperse aerosols is a useful method for the study of OPD and in conjunction with perfusion lung scintigraphy is helpful in the diagnosis of PE.

[Formation and migration of radioactive microemboli to the lung during radiovenography]. / Formación y migración de microembolias radiactivas al territorio pulmonar durante la radiovenografía.

Two patients with lower extremity thrombophlebitis were studied by radionuclide venography with macroaggregated albumin labelled with 99mTc. Data analysis was performed with a new method. It generated sequential series of imagen (1-2 sec/frame) of the transit of the tracer through leg, thigh, and abdomen, allowing a more precise definition of temporal changes on regional radioactivity. This method rendered the first real evidence of the binding of the tracer to pre-existent venous thrombi, of the dislodgement of these and their gradual fragmentation during their transit to the lungs. The patients had no complaints during or after the study. Lung scanning, performed 24 hours later, showed slight alteration on regional lung perfusion in one case, and none in the other. It is concluded that radioactive microemboli to the lungs is a minor complication of radionuclide venography, which does not justify prevention. This could only nullify the sensitivity of the procedure.

[Evaluation of radioactive phosphate scintillography in relation to time elapsed after acute myocardial infarct]. / Evaluación de la centelleografía con fosfatos radiactivos en relación con el tiempo de evolución del infarto agudo del miocardio.

A consecutive series of 205 myocardial scans, performed with 99mTc-labeled phosphates, in 185 patients with acute chest pain, were independently evaluated by comparing myocardial concentration intensity of the tracer to that in bone, and by rating this intensity by a six-category rating scale, which imply five criterion levels for calling an image "positive". The optimal criterion level was determined for each day of evolution of illness, as the one in which a shift to a more lax criterion level produces a bigger increment in false-positive results than in True-positive results, and in which a shift to a stricter criterion level causes a greater decrease in true positive results than in false-negative results. In all instances, the optimal criterion level was that with a moderate (2+) myocardial tracer concentration, lower than rib uptake, but with a focal pattern of myocardial distribution of the tracer (2F). By using this optimal criterion level, our results agree with the general consensus in that the procedure's usefullness is restricted to the first five days of evolution of illness. However, our daily statistical analysis showed that the best period to obtain the maximal diagnostic efficiency lies between the third and fourth days after the onset of acute chest pain. A negative result during this period, in patients with ECG and CPK serum concentration compatible with acute myocardial infarction, should be considered of prognostic significance, since it may translate a defficient colateral coronary circulation.

[Evaluation of the experience of the observer in the interpretation of myocardial scintillography with radioactive phosphates]. / Valoración de la experiencia del observador en la interpretación de la centelleografía del miocardio con fosfatos radiactivos.

Two-hundred-and five myocardial scans with radioactive phosphates, performed in 185 patients interned at the Coronary Care Unit due to acute chest pain (147 myocardial infarcts: 58 coronary heart disease), were independently interpreted by six observers with different degrees of experience on the lectures of these kind of images (two nuclear physicians, two cardiologists, and two fellows of the Nuclear Medicine Unit). A series of six different grades of myocardial concentration of the radioactive phosphates, related to its osseous concentration were followed. Each observer reported the grade of concentration he found in each image. The fraction of myocardial infarcts and of coronary heart disease found by each observer in every grade of concentration were calculated. With these data, it was determined the optimal criterion level of each observer by which he attained the minor incidence of false negative and false positive results. Four observers found their optimal criterion level on 2F, where grades 0-2D are considered as negative, and grades 2F-4 are considered as positive. One observer found his optimal level at 2D (0-1: -; 2D-4: +) and other at 1 (0: -; 1-4: +. By using a decision matrix which relates results of the test with a binary outcome (normal, abnormal) to the actual diagnosis, also with a binary outcome (infarct, no infarct), the ratios for "sensitivity", "specificity" and "accuracy" were derived for each observer performing at his particular optimal criterion level. Our results suggests that the observer performance depends on his particular degree of experience in interpreting nuclear medical images and on his visual perception. It was concluded that it is necessary to periodically evaluate the individual optimal criterion level of the physicians in charge of the lectures of the myocardial images with radioactive phosphates, liable to shift with time in relation to the experience of the observer. The need of a more objective procedure to quantitate myocardial concentration of the radioactive phosphates is also implied.